Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
How to Use This Presentation • To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” • To advance through the presentation, click the right-arrow key or the space bar. • From the resources slide, click on any resource to see a presentation for that resource. • From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. • You may exit the slide show at any time by pressing the Esc key. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Resources Chapter Presentation Bellringer Transparencies Sample Problems Visual Concepts Standardized Test Prep Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Atoms and Moles Table of Contents Section 1 Substances Are Made of Atoms Section 2 Structure of Atoms Section 3 Electron Configuration Section 4 Counting Atoms Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Bellringer • Make a list of inferences about any properties of objects in the box. • How could you learn more about the objects in the box without opening the box? • Scientist face these same questions as they try to learn more about atoms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Objectives • State the three laws that support the existence of atoms. • List the five principles of John Dalton’s atomic theory. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 1 Substances Are Made of Atoms Chapter 3 Atomic Theory • The idea of an atomic theory is more than 2000 years old. Aristotle modified an earlier theory that matter was made of four “elements”: earth, fire, water, air. Aristotle Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Democritus Democritus (430-370 BC), a Greek philosopher, believed that all Matter consists of very small, indivisible particles. He called these particles atomos (Greek for “uncuttable” or “indivisible”). Democritus’ idea, supported by experimental evidence nearly 2500 years later, laid the foundations for our modern understanding of the nature of elements and compounds. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • Until recently, scientists had never seen evidence of atoms. • The law of definite proportions, the law of conservation of mass and the law of multiple proportions support the current atomic theory. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Atomic Theory, continued • The figure on the right is a more accurate representation of an atom than the figure on the left. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Atomic Theory, continued The Law of Definite Proportions Joseph Proust (1754-1826), in 1799. Proust’s Law of Definite Proportions states: • The law of definite proportions states that a chemical compound always contains the same elements in exactly the same proportions by weight or mass. • The law of definite proportions also states that every molecule of a substance is made of the same number and types of atoms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Law of Definite Proportions PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Atomic Theory, continued The Law of Conservation of Mass Law of Conservation of Mass: Antoine Lavoisier consider “the father of modern chemistry” • The law of conservation of mass states that mass cannot be created or destroyed in ordinary chemical and physical changes. • The mass of the reactants is equal to the mass of the products. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Law of Conservation of Mass Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Law of Conservation of Mass, continued Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Law of Conservation of Mass PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Atomic Theory, continued The Law of Multiple Proportions • Proposed by John Dalton • The law of multiple proportions states that when two elements combine to form two or more compounds, the mass of one element that combines with a given mass of the other is in the ratio of small whole numbers. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Law of Multiple Proportions Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Law of Multiple Proportions PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Dalton’s Atomic Theory • In 1808, John Dalton developed an atomic theory. • Dalton believed that a few kinds of atoms made up all matter. • According to Dalton, elements are composed of only one kind of atom and compounds are made from two or more kinds of atoms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Dalton’s Atomic Theory , continued Dalton’s Theory Contains Five Principles 1. All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. 2. Atoms of a given element are identical in their physical and chemical properties. 3. Atoms of different elements differ in their physical and chemical properties. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 1 Substances Are Made of Atoms Dalton’s Atomic Theory , continued Dalton’s Theory Contains Five Principles, continued 4. Atoms of different elements combine in simple, whole-number ratios to form compounds. 5. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. • Data gathered since Dalton’s time shows that the first two principles are not true in all cases. • Hwk page 78 Que. 1,2,3,4,5,6 Quiz to Follow Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Bellringer • Look at the following terms: electron, nucleus, proton, neutron, atomic number, mass number, isotope • Chapter 3 Sec 2 Video Intro • Make a list of the terms that are unfamiliar to you? • After completing this section, look over your list to check that you are familiar with and understand all of the terms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Objectives • Describe the evidence for the existence of electrons, protons, neutrons, and describe the properties of these subatomic particles. • Discuss atoms of different elements in terms of their numbers of electrons, protons, neutrons, and define the terms atomic number and atomic mass. • Define isotope, and determine the number of particles in the nucleus of an isotope. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles • Experiments by several scientists in the mid-1800s led to the first change to Dalton’s atomic theory. Scientists discovered that atoms can be broken into pieces after all. • The smaller parts that make up atoms are called subatomic particles. • The three subatomic particles that are most important for chemistry are the electron, the proton, and the neutron. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Electrons Were Discovered Using Cathode Rays • To study current, J. J. Thomson pumped most of the air out of a glass tube. He applied a voltage to two metal plates, called electrodes, which were placed at either end of the tube. • One electrode, called the anode, was attached to the positive terminal of the voltage source, so it had a positive charge. • The other electrode, called a cathode, had a negative charge because it was attached to the negative terminal of the voltage source. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Electrons Were Discovered Using Cathode Rays, continued • Thomson observed a glowing beam that came out of the cathode and struck the anode and the nearby glass walls of the tube. • He called these rays cathode rays. • The glass tube Thomson used is known as a cathode-ray tube (CRT). • CRTs are used in television sets, computer monitors, and radar displays. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued An Electron Has a Negative Charge • Because the cathode ray came from the negatively charged cathode, Thomson reasoned that the ray was negatively charged. • Thomson confirmed this prediction by seeing how electric and magnetic fields affected the cathode ray. • Thomson also observed that when a small paddle wheel was placed in the path of the rays, the wheel would turn. • This suggested that the cathode rays consisted of tiny particles that were hitting the paddles of the wheel. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Thompson’s Cathode Ray Tube Experiment PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. United Streaming (Discovery) Search Cathode rays to xrays Program overview VIDEO Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued An Electron Has a Negative Charge, continued • Thomson’s experiments showed that a cathode ray consists of particles that have mass and a negative charge. • These particles are called electrons. • An electron is a subatomic particle that has a negative electric charge. • Electrons are negatively charged, but atoms have no charge. • Atoms contain some positive charges that balance the negative charges of the electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued An Electron Has a Negative Charge, continued • Properties of Electrons Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued • Thomson proposed that the electrons of an atom were embedded in a positively charged ball of matter. His model of an atom was named the plum-pudding model. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Rutherford Discovers the Nucleus, continued • Ernest Rutherford performed the gold foil experiment, which disproved the plum-pudding model of the atom. • Rutherford’s Expt. • A beam of small, positively charged particles, called alpha particles, was directed at a thin gold foil. • Rutherford’s team measured the angles at which the particles were deflected from their former straight-line paths as they came out of the foil. • Rutherford found that most of the alpha particles shot at the foil passed straight through the foil. But very few were deflected, in some cases backward. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Gold Foil Experiment Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Rutherford Discovers the Nucleus, continued • Rutherford reasoned that only a very concentrated positive charge in a tiny space within the gold atom could possibly repel the fast-moving, alpha particles enough to reverse the alpha particles’ direction. • Rutherford also hypothesized that the mass of this positive-charge containing region, called the nucleus, must be larger than the mass of the alpha particle. • Rutherford argued that the reason most of the alpha particles were undeflected, was that most parts of the atoms in the gold foil were empty space. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Gold Foil Experiment on the Atomic Level Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Rutherford Discovers the Nucleus, continued • The nucleus is the dense, central portion of the atom. • The nucleus is made up of protons and neutrons. • The nucleus has all of the positive charge, nearly all of the mass, but only a very small fraction of the volume of the atom. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Rutherford’s Gold Foil Experiment PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Proton and Neutrons Compose the Nucleus • Protons are the subatomic particles that have a positive charge and that is found in the nucleus of an atom. • The number of protons of the nucleus is the atomic number, which determines the identity of an element. • Because protons and electrons have equal but opposite charges, a neutral atom must contain equal numbers of protons and electrons. • Neutrons are the subatomic particles that have no charge and that is found in the nucleus of an atom. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Proton and Neutrons Compose the Nucleus, continued • Properties of a Proton and a Neutron Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Symbol Charge Mass Relative Charge Relative Mass Electron e- -1.602 x 10-19 C 9.109 x 10-31 kg 1- 1 Proton p+ +1.602 x10-19 C 1.673 x 10-27 kg 1+ 1837 Neutron n0 0C 1.675 x 10-27 kg 0 1839 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Parts of an Atom PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Protons and Neutrons Can Form a Stable Nucleus • Coulomb’s law states that the closer two charges are, the greater the force between them. • The repulsive force between two protons is large when two protons are close together. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Subatomic Particles, continued Protons and Neutrons Can Form a Stable Nucleus • Protons form stable nuclei despite the repulsive force between them. • A strong attractive force between these protons overcomes the repulsive force at small distances. • Because neutrons also add attractive forces, some neutrons can help stabilize a nucleus. (Act as glue) • All atoms that have more than one proton also have neutrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number Atomic Number Is the Number of Protons of the Nucleus • The number of protons that an atom has is known as the atom’s atomic number. • The atomic number is the same for all atoms of an element. • Because each element has a unique number of protons in its atoms, no two elements have the same atomic number. • Example: the atomic number of hydrogen is 1 because the nucleus of each hydrogen atom has one proton. The atomic number of oxygen is 8. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Atomic Number Is the Number of Protons of the Nucleus, continued • Atomic numbers are always whole numbers. • The atomic number also reveals the number of electrons in an atom of an element. • For atoms to be neutral, the number of negatively charged electrons must equal the number of positively charged protons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Atomic Number Is the Number of Protons of the Nucleus, continued • The atomic number for oxygen tells you that the oxygen atom has 8 protons and 8 electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Atomic Number Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued • The mass number is the sum of the number of protons and neutrons in the nucleus of an atom. • You can calculate the number of neutrons in an atom by subtracting the atomic number (the number of protons) from the mass number (the number of protons and neutrons). mass number – atomic number = number of neutrons • Unlike the atomic number, the mass number can vary among atoms of a single element. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued • Example: a particular atom of neon has a mass number of 20. • Because the atomic number for an atom of neon is 10, neon has 10 protons. number of protons and neutrons (mass number) = 20 number of protons (atomic number) = 10 number of neutrons = 10 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Mass Number Is the Number of Particles of the Nucleus, continued • The neon atom has 10 protons, 10 electrons, and 10 neutrons. The mass number is 20. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Mass Number Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Determining the Number of Particle In An Atom Sample Problem A How many protons, electrons, and neutrons are present in an atom of copper whose atomic number is 29 and whose mass number is 64? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Sample Problem A Solution • The atomic number indicates the number of protons in the nucleus of a copper atom. atomic number (29) = number of protons = 29 • A copper atom must be electrically neutral, so the number of electrons equals the number of protons. number of protons = number of electrons = 29 • The mass number indicates the total number of protons and neutrons mass number (64) - atomic number (29) = number of neutrons = 35 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols • Each element has a name, and the same name is given to all atoms of an element. • Example: sulfur is composed of sulfur atoms. • Each element has a symbol, and the same symbol is used to represent one of the element’s atoms. • Atomic number and mass number are sometimes written with an element’s symbol. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number • All atoms of an element have the same atomic number and the same number of protons. Atoms do not necessarily have the same number of neutrons. • Atoms of the same element that have different numbers of neutrons are called isotopes. • One standard method of identifying isotopes is to write the mass number with a hyphen after the name of an element. helium-3 or helium-4 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols A X Z A is the mass number Z is the atomic number X is the element symbol or Ex) Element Name-Mass Number 239 U 92 Uranium-239 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 Structure of Atoms Chapter 3 Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols • The atomic number always appears on the lower left side of the symbol. H 1 He 3Li Be 2 4 B 5 • Mass numbers are written on the upper left side of the symbol. 1 H 2 H 3 He 4 He 6 Li 7 Li Chapter menu 9 Be 10 B 11 B Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 2 Structure of Atoms Chapter 3 Atomic Number and Mass Number, continued Atomic Structures Can Be Represented by Symbols • Both numbers may be written with the symbol. 1 1 H 4 2 He 7 3 Li 9 4 Be 11 5 B • An element may be represented by more than one notation. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued • The second method of identifying isotopes shows the composition of a nucleus as the isotope’s nuclear symbol. 3 2 He or 24He • All isotopes of an element have the same atomic number. However, their atomic masses are not the same because the number of neutrons of the atomic nucleus of each isotope varies. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued • The two stable helium isotopes are helium-3 and helium-4. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Atomic Number and Mass Number, continued Isotopes of an Element Have the Same Atomic Number, continued • The Stable Isotopes of Lead Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Isotopes and Nuclides PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Determining the Number of Particle In An Isotope Sample Problem B Calculate the numbers of protons, electrons, and neutrons in oxygen-17 and in oxygen-18. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Sample Problem B Solution • atomic number = number of protons = number of electrons = 8 • mass number - atomic number = number of neutrons For oxygen-17, 17 - 8 = 9 neutrons For oxygen-18, 18 - 8 = 10 neutrons Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Ex) Section 2 Structure of Atoms 32 S 16 Ex) 108 Ag2+ 47 Ex) 80 Br1- 35 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 2 Structure of Atoms Ex) Fluorine-19 Ex) Calcium-44 Ex) Write the symbol that has 34 protons, 34 electrons, and 46 neutrons. Ex) Write the symbol that has 17 protons, 18 electrons, and 17 neutrons. Ex) Write the symbol that has 79 protons, 77 electrons, and 118 neutrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Homework Worksheet Quiz to Follow Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Objectives • Compare the Rutherford, Bohr, and quantum models of an atom. • Explain how the wavelengths of light emitted by an atom provide information about electron energy levels. • List the four quantum numbers, and describe their significance. • Write the electron configuration of an atom by using the Pauli exclusion principle and the the aufbau principle. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Evolution of the Atom or Models of the Atom Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 1) John Dalton Model Billard Ball Model Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. 2) J.J. Thomson Model or Plum Pudding Model 1904 the electrons are like raisins dispersed in a pudding (positive charge cloud) seeds in a watermelon blue-berry muffin Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Atomic Models Rutherford’s Model Proposed Electron Orbits • The experiments of Rutherford’s team led to the replacement of the plum pudding model of the atom with a nuclear model of the atom. • Rutherford suggested that electrons, like planets orbiting the sun, revolve around the nucleus in circular or elliptical orbits. • Rutherford’s model could not explain why electrons did not crash into the nucleus. • The Rutherford model of the atom was replaced only two years later by a model developed by Niels Bohr. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Evolution of the Atom 3) Rutherford Model or Nuclear Atom Model 1911 positive dense center called the nucleus rest of atom empty space (electrons reside) Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Evolution of the Atom 4) Bohr Model or the Shell Model 1913 pictured the atom as a small positive nucleus with electrons orbiting around it in curved circular pathways Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Atomic Models, continued Bohr’s Model Confines Electrons to Energy Levels • According to Bohr’s model, electrons can be only certain distances from the nucleus. Each distance corresponds to a certain quantity of energy that an electron can have. • An electron that is as close to the nucleus as it can be is in its lowest energy level. • The farther an electron is from the nucleus, the higher the energy level that the electron occupies. • The difference in energy between two energy levels is known as a quantum of energy. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Niels Bohr (Born in Denmark 1885-1962) • Student of Rutherford Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Niels Bohr’s Model (1913) • Electrons orbit the nucleus in circular paths of fixed energy (energy levels). Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Max Plank E=hn E=energy n=frequency h=Plank’s constant 6.7x10-34Js Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Energy of Emitted Photon Energy of the emitted photon = Difference in energy between two states Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • Energy emitted by the electron as it leaps from the higher to the lower energy level is proportional to the frequency of the light wave. • Frequency define the color of visible light. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Niels Bohr’s Atom Cont’d • Electrons can jump from energy level to energy level. • Electrons absorb or emit light energy when they jump from one energy level to another. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Quantum • A quantum of energy is the amount of energy required to move an electron from one energy level to another. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The energy levels are like the rungs of a ladder but are not equally spaced. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Photons • Photons are bundles of light energy that is emitted by electrons as they go from higher energy levels to lower levels. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Excited State and Ground State • Ground state: the lowest possible energy level an electron can be at. • Excited state: an energy level higher than the ground state. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Emission Spectrum • Light emitted produces a unique emission spectrum. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Hydrogen Emission Spectrum Violet Blue Red Balmer Series Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Bohr Model for Hydrogen Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. • The Bohr model explained the emission spectrum of the hydrogen atom but did not always explain those of other elements. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Evolution of the Atom 5) Wave Mechanical Model or the Electron Cloud Model 1920’s Louis Victor de Broglie and Erwin Schrodinger suggested that because light seems to behave both as a wave and as a stream of particles, then the electron should exhibit both of these characteristics Orbitals (electron states) are nothing like orbits Similar to a cloud or firefly analogy (highest probability) Heisenberg Uncertainty Principle we will never know simultaneously the exact momentum and position of an electron Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Atomic Models, continued Electrons Act Like Both Particles and Waves • Thomson’s experiments demonstrated that electrons act like particles that have mass. • In 1924, Louis de Broglie pointed out that the behavior of electrons according to Bohr’s model was similar to the behavior of waves. • De Broglie suggested that electrons could be considered waves confined to the space around a nucleus. • As waves, electrons could have only certain frequencies which correspond to the specific energy levels. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts De Broglie and the Wave-Particle Nature of Electrons PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Atomic Models, continued Electrons Act Like Both Particles and Waves, continued • The present-day model of the atom takes into account both the particle and wave properties of electrons. • In this model, electrons are located in orbitals, regions around a nucleus that correspond to specific energy levels. • Orbitals are regions where electrons are likely to be found. • Orbitals are sometimes called electron clouds because they do not have sharp boundaries. Because electrons can be in other places, the orbital has a fuzzy boundary like a cloud. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Atomic Models, continued Electrons Act Like Both Particles and Waves, continued • According to the current model of an atom, electrons are found in orbitals. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Quantum Mechanical Model • • • • 1920’s Werner Heisenberg (Uncertainty Principle) Louis de Broglie (electron has wave properties) Erwin Schrodinger (mathematical equations using probability, quantum numbers) Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Werner Heisenberg: Uncertainty Principle • We can not know both the position and momentum of a particle at a given time. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Louis de Broglie, (France, 18921987) Wave Properties of Matter (1923) •Since light waves have a particle behavior (as shown by Einstein in the Photoelectric Effect), then particles could have a wave behavior. •de Broglie wavelength l= h mv Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Electron Motion Around Atom Shown as a de Broglie Wave Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Davisson and Germer (USA, 1927) confirmed de Broglie’s hypothesis for electrons. Electrons produced a diffraction pattern similar to x-rays. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Erwin Schrodinger, 1925 Quantum (wave) Mechanical Model of the Atom • Four quantum numbers are required to describe the state of the hydrogen atom. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Atomic Orbital: A region in space in which there is high probability of finding an electron. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Comparing Models of Atoms PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light • By 1900, scientists knew that light could be thought of as moving waves that have given frequencies, speeds, and wavelengths. Light waves are electromagnetic waves and light is a form of electromagnetic radiation (A form of energy called radiant energy that travels at the speed of light with wave-like behavior). All waves, whether they are water waves or electromagnetic waves, can be described in terms of four characteristics-amplitude, wavelength, frequency, and speed. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. The Nature of Waves • What is a wave? • A wave is a repeating disturbance or movement that transfers energy through matter or space Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Waves transfer energy not matter. The water waves below are carrying energy but are not moving. Waves can only exist as they have energy to carry. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. What are the parts of a wave? The crest is the highest point on a wave. The trough is the lowest point on a wave. The rest position of the wave is called the node or nodal line. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Electrons and Light • Characteristics of a wave. 1) The amplitude of a wave is the height of the wave measured from the origin to its crest, or peak. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light • Characteristics of a wave. 2) The wavelength, λ (lambda) is the distance between successive crests of the wave. It is the distance that the wave travels as it completes one full cycle of upward and downward motion. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light • Characteristics of a wave. 3) The frequency, v (nu) of a wave tells how fast the wave oscillates up and down. The frequency of light is measured by the number of times a light wave completes a cycle of upward and downward motion in one second. Thus, the unit for frequency is cycles per second. Because it is understood that cycles are involved, frequency is commonly expressed simply as "per second," which is written as s-1 or 1/s. A cycle per second is also called a hertz (Hz): 1 Hz = 1 s-1. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light 4) Light, regardless of its wavelength, moves through space at a constant speed of 3.00 x 108 meters per second (m/s), which is the speed of light, c Because light moves at a constant speed, there is a relationship between its wavelength and its frequency. The shorter the distance between the crests of the wave, the faster the wave oscillates up and down. That is, the shorter the wavelength, the greater the frequency. This relationship can be expressed in a simple equation. Using the symbol λ (the Greek letter lambda) for wavelength, v (the Greek letter nu) for frequency, and c for the speed of light, the relationship between wavelength and frequency is C=λv Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. C=λν λ is inversly proportional to the ν Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Characteristics of a Wave PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electromagnetic Spectrum Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Electromagnetic Spectrum Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued • The electromagnetic spectrum is all of the frequencies or wavelengths of electromagnetic radiation. • The wavelength of light can vary from 105 m to less than 10–13 m. • In 1905, Albert Einstein proposed that light also has some properties of particles. • His theory would explain a phenomenon known as the photoelectric effect. • This effect happens when light strikes a metal and electrons are released. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued • Einstein proposed that light has the properties of both waves and particles. • Light can be described as a stream of particles, the energy of which is determined by the light’s frequency. Light is an electromagnetic wave. • Red light has a low frequency and a long wavelength. • Violet light has a high frequency and a short wavelength. • The frequency and wavelength of a wave are inversely related. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued Light is an electromagnetic Wave, continued • The frequency and wavelength of a wave are inversely related. • As frequency increases, wavelength decreases. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Wavelength and Frequency Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued Light Emission • When a high-voltage current is passed through a tube of hydrogen gas at low pressure, lavender-colored light is seen. When this light passes through a prism, you can see that the light is made of only a few colors. This spectrum of a few colors on a black background that is related to electron transitions from higher energy levels to lower energy level s is called a line-emission spectrum. • Experiments with other gaseous elements show that each element has a line-emission spectrum that is made of a different pattern of colors. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued Light Emission, continued • In 1913, Bohr showed that hydrogen’s line-emission spectrum could be explained by assuming that the hydrogen atom’s electron can be in any one of a number of distinct energy levels. • An electron can move from a low energy level to a high energy level by absorbing energy. • Electrons at a higher energy level are unstable and can move to a lower energy level by releasing energy. This energy is released as light that has a specific wavelength. • Each different move from a particular energy level to a lower energy level will release light of a different wavelength. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued Light Provides Information About Electrons • An electron in a state of its lowest possible energy, is in a ground state. • The ground state is the lowest energy state of a quantized system • If an electron gains energy, it moves to an excited state. • An excited state is a state in which an atom has more energy than it does at its ground state • An electron in an excited state will release a specific quantity of energy as it quickly “falls” back to its ground state. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electrons and Light, continued Light Provides Information About Electrons, continued • An electron in a hydrogen atom can move between only certain energy states, shown as n = 1 to n = 7. • In dropping from a higher energy state to a lower energy state, an electron emits a characteristic wavelength of light. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Hydrogen’s Line-Emission Spectrum Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Absorption and Emission Spectra Chapter menu PLAY Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers • The present-day model of the atom is also known as the quantum model. • According to this model, electrons within an energy level are located in orbitals, regions of high probability for finding a particular electron. • The model does not explain how the electrons move about the nucleus to create these regions. Heinsenberg Uncertainity Principle • To define the region in which electrons can be found, scientists have assigned four quantum numbers that specify the properties of the electrons. • A quantum number is a number that specifies the properties of electrons. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers, continued 1) The principal quantum number, symbolized by n, indicates the main energy level occupied by the electron. • Values of n are positive integers, such as 1, 2, 3, 4, ∞ • As n increases, the electron’s distance from the nucleus and the electron’s energy increases. • Max # e- is 2n2 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Principal Quantum Number PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers, continued 2) The main energy levels can be divided into sublevels. These sublevels are represented by the angular momentum quantum number, l. • This quantum number indicates the shape or type of orbital that corresponds to a particular sublevel. • A letter code is used for this quantum number. • l = 0 corresponds to an s orbital • l = 1 to a p orbital • l = 2 to a d orbital • l = 3 to an f orbital Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers, continued 3) The magnetic quantum number, symbolized by m, is a subset of the l quantum number. • It also indicates the numbers and orientations of orbitals around the nucleus. • The value of m takes whole-number values, depending on the value of l. • The number of orbitals includes • • • • one s orbital three p orbitals five d orbitals seven f orbitals Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers, continued 4) The spin quantum number, ms indicates the orientation of an electron’s magnetic field relative to an outside magnetic field. • The spin quantum number is represented by: 1 1 + or or ( or ) 2 2 • A single orbital can hold a maximum of two electrons, which must have opposite spins. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Quantum Numbers and Orbitals PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Quantum Numbers, continued • Quantum Numbers of the First 30 Atomic Orbitals Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration • In 1925 the German chemist Wolfgang Pauli established a rule is known as the Pauli exclusion principle. • The Pauli exclusion principle states that two particles of a certain class cannot be in the exact same energy state. • This means that that no two electrons in the same atom can have the same four quantum numbers. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Pauli Exclusion Principle PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration • Two electrons can have the same value of n by being in the same main energy level. • These two electrons can also have the same value of l by being in orbitals that have the same shape. • These two electrons may also have the same value of m by being in the same orbital. • But these two electrons cannot have the same spin quantum number. • If one electron has the value of 1/2, then the other electron must have the value of –1/2. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Shapes of s, p, and d Orbitals Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Homework: Worksheet on Quantum Numbers QUIZ on Section 3 to this point next class Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations • The arrangement of electrons in the ground state of an atom is usually shown by writing an electron configuration or an orbital notation. • Like all systems in nature, electrons in atoms tend to assume arrangements that have the lowest possible energies. • An electron configuration of an atom shows the lowest-energy arrangement of the electrons for the element. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Electron configurations vs Orbital Notation Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Orbital Notation PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available • The aufbau principle states that electrons fill orbitals that have the lowest energy first. • Aufbau is the German word for “building up.” • The smaller the principal quantum number, the lower the energy. Within an energy level, the smaller the l quantum number, the lower the energy. • So, the order in which the orbitals are filled matches the order of energies. 1s < 2s < 2p < 3s < 3p Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available, continued • The energy of the 3d orbitals is slightly higher than the energy of the 4s orbitals. • As a result, the order in which the orbitals are filled is as follows: 1s < 2s < 2p < 3s < 3p < 4s < 3d • Additional irregularities occur at higher energy levels. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations, continued An Electron Occupies the Lowest Energy Level Available, continued • This diagrams shows how the energy of the orbitals can overlap. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Aufbau Principle PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. See Handout for notes Aufbau Principle a) Memorize b) Periodic table c) Diagonal Rule Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 4 Section 1 How Are Elements Organized? Blocks of the Periodic Table 4f 5f Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts s Orbitals PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts p Orbitals PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 d Orbitals Visual Concepts PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Electron Configuration PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 3 Electron Configuration Chapter 3 Electron Configurations, continued An Electron Configuration Is a Shorthand Notation, continued • Electron orbitals are filled according to Hund’s Rule. • Hund’s rule states that orbitals of the same n and l quantum numbers are each occupied by one electron before any pairing occurs. • Orbital diagram for sulfur 3p 3s 2p 2s 1s Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations, continued An Electron Configuration Is a Shorthand Notation • Based on the quantum model of the atom, the arrangement of the electrons around the nucleus can be shown by the nucleus’s electron configuration. • Example: sulfur has sixteen electrons. Its electron configuration is written as 1s22s22p63s23p4. • Two electrons are in the 1s orbital, two electrons are in the 2s orbital, six electrons are in the 2p orbitals, two electrons are in the 3s orbital, and four electrons are in the 3p orbitals. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Examples of both Electron Configuration and Orbital Notation 2 worksheets for homework. QUIZ to follow. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Electron Configurations, continued An Electron Configuration As a Shorthand Notation, continued • Each element’s configuration builds on the previous elements’ configurations. • To save space, one can write this configuration by using a configuration of a noble gas. • neon, argon, krypton, and xenon • The neon atom’s configuration is 1s22s22p6, so the electron configuration of sulfur is [Ne] 3s23p4 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Visual Concepts Noble Gas Notation PLAY Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Sample Problem C Writing Electron Configurations Write the electron configuration for an atom whose atomic number is 20. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 3 Electron Configuration Sample Problem C Solution • atomic number = number of protons = number of electrons = 20 • According to the aufbau principle, the order of orbital filling is 1s,2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on. • The electron configuration for an atom of this element is written as follows: 1s22s22p63s23p64s2 • This electron configuration can be abbreviated as follows: [Ar]4s2 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 • The electrons in the outer shell are called valence electrons. • Valence electrons are found in the outermost shell of an atom and that determines the atom’s chemical properties. • Elements with the same number of valence electrons tend to react in similar ways. • Because s and p electrons fill sequentially, the number of valence electrons in s- and p-block elements are predictable. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Valence Electrons • valence electrons are the electrons in the OUTERMOST energy level… that’s why we did all those electron configurations! • B is 1s2 2s2 2p1; so the outer energy level is 2, and there are 2+1 = 3 electrons in level 2. These are the valence electrons! • Br is [Ar] 4s2 3d10 4p5 How many valence electrons are present? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Valence Electrons Number of valence electrons of a main (A) group atom = Group number Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 H Li 18 He: Be B C Na Mg Al N Si O P S Chapter menu : F :Ne : :Cl :Ar : Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Worksheet for Homework Quiz to Follow Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Bellringer • A penny has 2.97 1022 copper atoms. • On a sheet of paper, write out this number in regular notation with all the zeros. • What does this tell you about the size of an atom? Chapter 3 Section 4 Counting Atoms Objectives • Compare the mass quantities and units for atomic mass with those for molar mass. • Define mole, and explain why this unit is used to count atoms. • Calculate either mass with molar mass or number with Avogadro’s number given an amount in moles. List some common Counting Units A counting unit Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,200,000,000,000,000,000,000 6.022 X 1023 (in scientific notation) This number is named in honor of Amedeo Avogadro(1776 – 1856) How we determine quantity: Counting, Weighing or Volume Measurement We will first consider how people normally keep track of quantity in everyday life. There are generally three ways to do this: • • • Counting by number of units. Example: oranges priced by number. If a single unit is too small, we devise a lump sum. Example: eggs are priced by the dozen, which is a lump sum of 12 units. Weighing by weight or mass. Example: meat is priced by the pound. Measuring by volume. This is easier to use with liquids or gases. Example: gasoline is priced by the gallon. Is it surprising to you that we employ similar ways in chemistry to keep track of atoms and molecules as described above? But, indeed we do. The next two slides compare two parallel ways of counting by number of units: As we count small items by the “dozen” in everyday life, we count atoms and molecules by the “mole” in chemistry. How many eggs are in 15 dozen eggs? How many dozens of donuts are in 26 donuts? How many atoms are in 57 dozen of Al atoms? How many dozen of atoms are in 1.8 * 105 Fe? How many atoms are in 57 mole of Al atoms? How many moles of atoms are in 1.8 * 105 Fe? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Previous slides showed how counting eggs in dozens is similar to counting atoms by the mole. We use similar math equations for both mole <--> number conversions and dozen <--> number conversions. Since everyday items contain astronomical numbers of atoms and molecules, it is easier to count them by a huge lump sum: 1 mole = 6.022 x 1023 But why do we use Avogadro’s number, 6.022 x 1023 , for one mole? Did he invent the number? No, neither he nor anyone else did. The number is defined by how the mass units, amu and gram, relate to each other: amu is the mass of one atom units are atomic mass unit 1 amu = 1.66058 x 10-24 grams Experimental data: 1 amu = 1.66058 x 10-24 grams leads to this equality: 6.022 x 1023 amu = 1 gram because: 1 / (1.66058 x 10-24) = 6.022 x 1023 Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Just How Big is a Mole? • If you had Avogadro's number of soft drink cans to cover the surface of the earth to a depth of over 200 miles. • If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. • If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole. Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Mole Trivia • If there were a mole of rice grains, all the land area in the whole world would be covered with rice to a depth of about 75 meters. • One mole of rice grains is more grains than all the grain that has been grown since the beginning of time. (1) • One mole of rice would occupy a cube about 120 miles on an edge! (1) Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Mole Trivia • A mole of marshmallows would cover the United States to a depth of 600 miles (3) • In order to put a mole of rain drops in a 30 meter (about 100 feet) diameter tank, the sides of the tank would have to be 280 times the distance from the Earth to the Sun. (4) • A mole of hockey pucks would be equal to the mass of the Moon. Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Mole Trivia • Assuming that each human being has 60 trillion body cells (6.0 x 1013) and the Earth's population is 6 billion (6 x 109), the total number of living human body cells on the Earth at the present time is 3.6 x 1023 or a little over half of a mole. Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Mole Trivia • If one mole of pennies were divided up among the Earth's population, each person would receive 1 x 1014 pennies. • Personal spending at the rate of one million dollars a day would use up each persons wealth in about three thousand years. • Life would not be comfortable because the surface of the Earth would be covered in copper coins to a depth of at least 400 meters. Mole Trivia The mole is a REALLY BIG number!!!! Just how big is it? Mole Trivia • If you had a mole of pennies and wanted to buy kite string at the rate of a million dollars per inch, you would get your money's worth. • After stretching your string around the Earth one million times, and to the Moon and back twentyfive times, you would have enough string left over to sell back at a dollar an inch (a decided loss) to gain enough money to buy every man, woman and child in the US a $50,000 automobile and enough gasoline to run it at 55 mph for a year. • After those purchases, you would still have enough money left over to give every man, woman, and child in the whole world about $5000. Mole Trivia • Basis for calculations: –Earth's circumference = 25,000 miles –Distance to moon = 240,000 miles –Cost of gasoline = $2.50 per gallon –Gasoline mileage = 20 miles per gallon –U.S. population =220,000,000 –World population = 6,000,000,000 • Given the chemical composition of an everyday item, we can easily determine the number of atoms or molecules present in it by applying the conversions we have practiced in the previous slides Avogadro’s Number • The standard laboratory unit of mass is the gram. • We would like to choose a number of atoms which would have a mass in grams equivalent to the mass of one atom in atomic mass units. • The same number would fit all elements since equal numbers of different atoms always have the same mass ratio. • There is one problem in using the molecular and formula masses of substances. • These masses are in atomic mass units, which is only 1.66 x 10-24 g. • The mass of a single molecule is so small that it is impossible to measure it in the laboratory. • For everyday use in chemistry, a larger unit, such as a gram, is needed. http://www.youtube.com/watch?v=TqDqLmwWx3A Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Atomic Mass, continued Masses of Atoms Are Expressed in Atomic Mass Units • A special mass unit is used to express atomic mass. • This unit has two names—the atomic mass unit (amu) and the Dalton (Da). Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Introduction to the Mole • Most samples of elements have great numbers of atoms. • A mole is defined as the number of atoms in exactly 12 grams of carbon-12.The mole is the SI unit for the amount of a substance. • The molar mass of an element is the mass in grams of one mole of the element. Molar mass has the unit grams per mol (g/mol). • The mass in grams of 1 mol of an element is numerically equal to the element’s atomic mass from the periodic table in atomic mass units. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Other Names Related to Molar Mass • Molecular Mass/Molecular Weight: If you have a single molecule, mass is measured in amu’s instead of grams. But, the molecular mass/weight is the same numerical value as 1 mole of molecules. Only the units are different. (This is the beauty of Avogadro’s Number!) • Formula Mass/Formula Weight: Same goes for compounds. But again, the numerical value is the same. Only the units are different. • THE POINT: You may hear all of these terms which mean the SAME NUMBER… just different units Learning Check! Find the molar mass (usually we round to the hundreths place) A. 1 mole of Br atoms = B. 1 mole of Sn atoms = 79.90 g/mole 118.69 g/mole Chapter 3 Visual Concepts Molar Mass Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Calculations with Molar Mass molar mass Grams Moles What is in a Mole? It is important to note that; one mole of atoms = 6.022 x 1023 atoms one mole of atoms= molar mass in grams 1 mole of Cu = 6.022 x 1023 atoms of Cu 1 mole of Cu = 63.55 g of Cu mol= ___________atoms atoms=__________mol g=_____________mol mol=____________g g=____________atoms atoms=__________g These problems can be solved in TWO ways: 1) Factor Label Method (conversion factors)(proportions) We know that: 1 mole of a element = 6.022 x 1023 atoms of that element = molar mass (atomic weight) in grams Given (units given) 1 x Conversion ( units of unknown) factor (units of given) = desired answer Avogadro’s Number as Conversion Factor 6.022 x 1023 particles 1 mole or 1 mole 6.02 x 1023 particles Note that a particle could be an atom OR a molecule! Using Formulas Molar Mass = mass ÷ moles Mass (grams of the subs.) = (moles) (Molar Mass) Moles = Mass (grams of the subs.) ÷ Molar Mass Number of Particles = (Moles) (Avogadro’s #) Ex) What is the mass in grams of 0.586 mol Zn atoms? Converting Moles and Grams Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al 1. Molar mass of Al 1 mole Al = 27.0 g Al 2. Conversion factors for Al 27.0g Al 1 mol Al or 1 mol Al 27.0 g Al 3. Setup 3.00 moles Al Answer x 27.0 g Al 1 mole Al = 81.0 g Al Atoms/Molecules and Grams • Since 6.02 X 1023 particles = 1 mole AND 1 mole = molar mass (grams) • You can convert atoms/molecules to moles and then moles to grams! (Two step process) • You can’t go directly from atoms to grams!!!! You MUST go thru MOLES. • That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first! Calculations molar mass Grams Avogadro’s number Moles particles Everything must go through Moles!!! Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu Cu 1 mol Cu 6.02 X 1023 atoms 63.5 g Cu 1 mol Cu = 3.4 X 1023 atoms Cu Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Learning Check! How many atoms of K are present in 78.4 g of K? Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Learning Check! How many atoms of O are present in 78.1 g of oxygen? 78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2 Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Converting from Amount in Moles to Mass Sample Problem D Determine the mass in grams of 3.50 mol of copper. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Sample Problem D Solution • First, make a set-up that shows what is given and what is desired. 3.50 mol Cu ? = ? g Cu • Use a conversion factor that has g Cu in the numerator and mol Cu in the denominator. ? g Cu 3.50 mol Cu = ? g Cu 1 mol • The correct conversion factor is the molar mass of Cu, 63.55 g/mol. 63.55 g Cu 3.50 mol Cu = 222 g Cu 1 mol Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Converting from Amount in Moles to Number of Atoms Sample Problem E Determine the number of atoms in 0.30 mol of fluorine atoms. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 3 Section 4 Counting Atoms Sample Problem E Answer • To determine the number of atoms, select the conversion factor that will take you from the amount in moles to the number of atoms. amount (mol) 6.022 1023 atoms/mol = number of atoms 6.022 1023 F atoms 3.50 mol F = 1 mol F 1.8 1023 F atoms Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Ex) How many moles are in 2.83 * x 1025 atoms Cr? Ex) How many moles are in 6.195 g of K? Ex) How many grams are in 9.76 x 1024 atoms of Ba? Determining Moles of Atoms Aluminum (Al) is a metal with a high strength-to-mass ratio and a high resistance to corrosion: thus it is often used for structural purposes. 1. Compute the number of moles in a 10.0 gram sample of Aluminum 2. Compute the number of atoms in the same sample. Answers 1. 0.371 mol Al atoms 2. 2.23 x 1023 atoms Calculating Numbers of Atoms A silicon chip used in an integrated circuit of a microcomputer has a mass of 5.68 mg. How many silicon (Si) atoms are present in the chip? Answer 1.22 x 1020 atoms Calculating Number of Moles and Mass Cobalt (Co) is a metal that is added to steel to improve its resistance to corrosion. Calculate both the number of moles and the number of grams in a sample of cobalt containing 5.00 x 1020 atoms of cobalt. Answers 8.30 x 10-4 mol Co 4.89 x 10-2 g Co •STOP •ASSIGN WORKSHEET FOR HOMEWORK •QUIZ NEXT CLASS •CHAPTER 3 TEST UPCOMING