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Lecture Presentation Chapter 4 Elements and Symbols Karen C. Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chapter 4 Atoms and Elements In addition to growing crops and raising animals, farmers must understand how to perform chemical tests and how to apply fertilizers and pesticides or herbicides to crops. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chapter 4 Readiness Key Math Skills • Using Positive and Negative Numbers in Calculations (1.4B) • Calculating Percentages (1.4C) • Rounding Off (2.3) Core Chemistry Skills • Counting Significant Figures (2.2) • Using Significant Figures in Calculations (2.3) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.1 Elements and Symbols Elements • are pure substances from which all other things are built. • cannot be broken down into simpler substances. • are listed on the inside front cover of this text. Learning Goal Given the name of an element, write its correct symbol; from the symbol, write the correct name. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Some Elements and Their Names Element names come from planets, mythological figures, minerals, colors, geographic locations, and famous people. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemical Symbols Chemical symbols • represent the names of the elements. • consist of one to two letters and start with a capital letter. One-Letter Symbols C carbon N nitrogen F fluorine O oxygen General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Two-Letter Symbols Co cobalt Ca calcium Al aluminum Mg magnesium © 2016 Pearson Education, Inc. Names and Symbols of Common Elements General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemical Symbols from Latin Names Ag silver (argentum) Au gold (aurum) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write the correct chemical symbols for each of the following elements: A. B. C. D. E. iodine iron magnesium zinc nitrogen General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Give the names of the elements with the following symbols: A. B. C. D. E. P Al Mn H K General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Toxicity of Mercury Mercury (Hg) • is a silvery, shiny element that is a liquid at room temperature. • can enter the body by mercury vapor inhalation, contact with the skin, or ingestion of water or food contaminated with mercury. Once mercury has entered the body, it destroys proteins and disrupts cell function. Long-term exposure can • damage the brain and kidneys. • cause mental retardation. • decrease physical development. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Chemistry Link to Health: Toxicity of Mercury Mercury contamination comes from • industrial wastes. • fish and seafood. • batteries. • compact fluorescent bulbs. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.2 The Periodic Table The periodic table organizes 118 elements into groups with similar properties and places them in order of increasing atomic mass. Learning Goal Use the periodic table to identify the group and the period of an element; identify the element as a metal, a nonmetal, or a metalloid. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Periodic Table of Elements • First proposed by Russian Chemist Dmitiri Mendeleev in 1869 • Organized the known elements by similarities in physical and chemical properties and then my increasing atomic “weights,” as they were know back then. Today, we call it atomic mass • Since 1915, the elements have been arranged by increasing atomic number General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Periodic Table of Elements General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Groups and Periods In the periodic table, • elements are arranged according to properties. • groups contain elements with similar properties in vertical columns. • periods are horizontal rows of elements, counted from top to bottom of the table as Periods 1−7. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Groups and Periods Vertical columns represent groups of elements, and horizontal rows represent periods. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Group Numbers Group numbers are written at the top of each vertical column. • Use the letter A for representative elements (Groups 1A–8A). • Use the letter B for transition elements (Groups 3B–12B). An alternative system uses numbers of 1–18 for all of the groups, from left to right, across the periodic table. Because both systems are currently in use, they are both shown on the periodic table in this text and are included in our discussions of elements and group numbers. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Group Names – some groups have common names General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Alkali Metals Group 1A (1), the alkali metals, includes the following: • lithium (Li) • sodium (Na) • potassium (K) • rubidium (Rb) • cesium (Cs) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Alkaline Earth Metals Group 2A (2) elements, the alkaline earth metals, are shiny but not as reactive as Group 1A metals. They include the following: • beryllium (Be) • magnesium (Mg) • calcium (Ca) • strontium (Sr) • barium (Ba) • radium (Ra) Strontium gives the red color in fireworks. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Halogens Group 7A (17), the halogens, includes the following: • fluorine (F) • chlorine (Cl) • bromine (Br) • iodine (I) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Noble Gases Group 8A (18) is the noble gases, which include helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Ra). Noble gas elements are extremely unreactive (i.e. they are seldom found in combination with other elements). Were not discovered until the 1890s because of their inactivity, so they were not on Mendeleev’s original table © 2013 Pearson Education, Inc. Chapter 3, Section 2 23 Study Check Identify the element described by each of the following groups and periods: 1. Group 7A (17), Period 4 A. Br B. Cl C. Mn 2. Group 2A (2), Period 3 A. beryllium B. boron C. magnesium 3. Group 5A (15), Period 2 A. phosphorus B. arsenic C. nitrogen General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 3 Categories of Elements: Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. • Metals are located to the left. • Nonmetals are located to the right. • Metalloids are located along the heavy zigzag line. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Characteristics of Metals, Nonmetals, and Metalloids Metals, except for hydrogen, located on the left of the periodic table, • are shiny and ductile, and conduct heat and electricity. • are solids, except for mercury (Hg), which is a liquid. Nonmetals, located on the right side of the periodic table, • are dull, brittle, and poor conductors but often good insulators. • have low densities and melting points. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Characteristics of Metals, Nonmetals, and Metalloids Metalloids, located along the heavy zigzag line on the periodic table, • exhibit properties of metals and nonmetals. • are better conductors than nonmetals but not as good as metals. • are used as semiconductors and insulators, because they can be modified to function as conductors or insulators. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Comparing a Metal, a Nonmetal, and a Metalloid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Identify each of the following elements as a metal, a nonmetal, or a metalloid: A. sodium B. chlorine C. silicon D. iron E. carbon General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check List all of the elements that match the description. A. metals in Group 4A (14) Sn, Pb, C, Si, Ge B. nonmetals in Group 5A (15) Bi, N, P, As, Sb C. metalloids in Group 4A (14) C, Si, Ge, Sn, Pb General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.3 The Atom – A Brief History of Atomic Theory An atom is the smallest particle of an element that retains the characteristics of that element. Aluminum foil contains atoms of aluminum. Learning Goal Describe the electrical charge and location in an atom for a proton, a neutron, and an electron. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. John Dalton’s Atomic Theory ( circa 1808) Dalton theorized that Atoms are tiny particles of matter too small to see, are able to combine with other atoms to make compounds, and are similar to each other for each element and different from atoms of other elements. A chemical reaction is the rearrangement of atoms. Atoms are never created or destroyed during chemical and physical changes © 2013 Pearson Education, Inc. Dalton envisioned atoms to be solid, indivisible spheres, like billiard balls called the “billiard ball model” Chapter 3, Section 3 32 Atomic Theory in the late 1890’s Discovery of radioactivity and the discovery of the first subatomic particle (the electron) meant Dalton’s solid sphere model had to change. JJ Thomson, discoverer of the electron, developed “plum pudding model.” Electron was tiny (1/2000th the size of the atom), negatively charged particle As atom electrically neutral, electron must be embedded in “positive dough” of atom like plums in plum pudding © 2013 Pearson Education, Inc. Chapter 3, Section 1 33 Electrical Charges in an Atom Atoms contain the following subatomic particles: • protons that have a positive (+) charge • electrons that have a negative (–) charge • neutrons that have no charge (neutral) Like charges repel and unlike charges attract. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. J. J. Thomson’s Cathode Ray Tube Exp From his experiment, J. J. Thomson realized that • cathode rays contain negatively charged particles. • particles (now called electrons) have a much smaller mass than the atom. Thomson proposed a “plum-pudding” model of the atom in which protons and electrons were randomly distributed in a positively charged cloud, like plums in a pudding. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. J. J. Thomson’s Plum Pudding Model (1897) Thomson’s “plum-pudding” model had protons and electrons scattered throughout the atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Rutherford’s Gold Foil Experiment (1911) In Rutherford’s gold foil experiment, positively charged particles • were aimed at atoms of gold. • mostly went straight through the atoms. • were deflected only occasionally. Rutherford’s experiment concluded that there must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Rutherford’s Gold Foil Experiment (a) Positive particles are aimed at a piece of gold foil. (b) Particles that come close to the atomic nuclei are deflected from their straight path. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Rutherford’s Nuclear Model of the Atom (1911) The atom is mostly empty space All of the positive charge is located in a tiny, dense nucleus The negative electrons are located at a distance away and must be constantly moving to avoid being pulled into the nucleus 39 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Discovery of Proton and Neutron Positive charge comes in nucleus actually due to a particle, called the proton (Rutherford, 1919) More mass in the nucleus than protons could account for in 1932, an electrically neutral particle called the “neutron” was discovered by James Chadwick. 40 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Structure of the Atom An atom consists of • a nucleus, located in the center of the atom, that contains protons and neutrons and represents most of the mass of an atom. • electrons that occupy a large, empty space around the nucleus. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Structure of the Atom In an atom, the protons and neutrons that make up almost all the mass are packed into the tiny volume of the nucleus. The rapidly moving electrons (negative charge) surround the nucleus and account for the large volume of the atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Mass of the Atom Because the mass of subatomic particles is so small, • chemists use a very small unit of mass called the atomic mass unit (amu). • 1 amu has a mass equal to 1/12 of the mass of the carbon-12 atom that contains six protons and six neutrons. • 1 amu = 1 Dalton (Da) in biology. • Electrons have such a small mass that they are not included in the mass of an atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Subatomic Particles in the Atom Subatomic particles have a very small mass, and an electron has a mass that is much less than that of a proton or a neutron. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Which of the following subatomic particles fits each of the descriptions below? protons, neutrons, or electrons A. found outside the nucleus B. have a positive charge C. have mass but no charge General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.4 Atomic Number and Mass Number All atoms of an element have the same number of protons and the same atomic number. Learning Goal Given the atomic number and the mass number of an atom, state the number of protons, neutrons, and electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atomic Number The atomic number • is a whole number specific for each element. • is the same for all atoms of an element. • is equal to the number of protons in an atom. • appears above the symbol of an element in the periodic table. Atomic number Symbol General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake 11 Na © 2016 Pearson Education, Inc. Atomic Number = Protons in an Atom Atomic number = number of protons—for example, • the atomic number of H is 1; every H atom has one proton. • the atomic number of C is 6; every C atom has six protons. • the atomic number of Cu is 29; every Cu atom has 29 protons. Core Chemistry Skill Counting Protons and Neutrons General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atomic Number = Protons in an Atom All atoms of lithium (left) contain three protons, and all atoms of carbon (right) contain six protons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atoms are Neutral For neutral atoms, the net charge is zero. number of protons = number of electrons Aluminum has 13 protons and 13 electrons. The net (overall) charge is zero. 13 protons (13+) + 13 electrons (13–) = 0 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Use the periodic table to fill in the atomic number, number of protons, and number of electrons for each of the following elements: Element Atomic Number N Protons Electrons Zn S General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Mass Number The mass number • represents the number of particles in the nucleus. • is equal to the number of protons + the number of neutrons. • is always a whole number. • does not appear in the periodic table. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Composition of Some Atoms of Different Elements General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Tips: Protons and Neutrons Number of protons = atomic number Number of protons + neutrons = mass number Number of neutrons = mass number – atomic number Note: Mass numbers are given for specific isotopes only. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check An atom of lead (Pb) has a mass number of 207. A. How many protons are in the nucleus? B. How many neutrons are in the nucleus? C. How many electrons are in the atom? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.5 Isotopes and Atomic Mass 24 12 Mg The atomic symbol for an isotope of magnesium with 12 neutrons. Learning Goal Determine the number of protons, electrons, and neutrons in one or more of the isotopes of an element; calculate the atomic mass of an element using the percent abundance and mass of its naturally occurring isotopes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Isotopes Isotopes • are atoms of the same element. • have different mass numbers. • have the same number of protons but different numbers of neutrons. • can be distinguished by their atomic symbols. Core Chemistry Skill Writing Atomic Symbols for Isotopes General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atomic Symbols: Subatomic Particles Given the atomic symbols, determine the number of protons, neutrons, and electrons. 16 8 O 31 15 P 65 30 ANALYZE THE PROBLEM Zn Atomic Number number in lower left corner General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Mass Number number in upper left corner Number of Protons equal to atomic number © 2016 Pearson Education, Inc. Atomic Symbols: Subatomic Particles Determine the number of protons, neutrons, and electrons. Isotope Atomic Number Mass Number of Number of O Number Protons Neutrons 16 8 16 8 31 15 O 8 16 8 8 (16–8) P 15 31 15 16 (31–16) 65 30 Zn 30 65 30 35 (65–30) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Isotopes of Magnesium Magnesium, with three naturally occurring isotopes, has an atomic mass of 24.31 amu. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Isotopes of Magnesium General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Naturally occurring carbon consists of three isotopes: 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the three isotopes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write the atomic symbols for atoms with the following subatomic particles: A. 8 protons 8 neutrons 8 electrons B. 17 protons 20 neutrons 17 electrons C. 47 protons 60 neutrons 47 electrons General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check 1. Which of the pairs below are isotopes of the same element? 2. In which of the pairs below do both atoms have eight neutrons? A. 15 8 B. 12 6 C. 15 7 X 15 7 X X 14 6 X X 16 8 X General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Calculating Average Atomic Mass Atomic mass is the • weighted average of all naturally occurring isotopes of that element. • number on the periodic table below the chemical symbol. Chlorine, with two naturally occurring isotopes, has an atomic mass of 35.45 amu. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Calculating Average Atomic Mass To calculate atomic mass, • use the experimental percent abundance of each isotope of the element. • multiply the percent abundance by the atomic mass of that isotope. • sum the total mass of all isotopes. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Calculating Average Atomic Mass To calculate atomic mass of chlorine, use experimental data for both isotopes. Atomic mass of Mg = 18.88 amu + 2.531 amu + 2.902 amu = 24.31 amu (weighted average mass) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Average Atomic Masses of Some Elements General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Lithium consists of two naturally occurring isotopes, 6Li and 7Li. Use the periodic table to predict which isotope is the more prevalent one. (According to the periodic table, the atomic mass of lithium is 6.941 amu.) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.10% of 69Ga (atomic mass 68.926) atoms 39.90% of 71Ga (atomic mass 70.925) atoms What is the atomic mass of gallium? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.6 Electron Energy Levels A rainbow forms when light passes through water droplets. Learning Goal Describe the energy levels, sublevels, and orbitals for the electrons in an atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electromagnetic Radiation We experience electromagnetic radiation in different forms, such as light, the colors of a rainbow, or X-rays. Electromagnetic radiation consists of energy particles that move as waves of energy. • The distance between the peaks of waves is called the wavelength. • High-energy radiation has shorter wavelengths. • Low-energy radiation has longer wavelengths. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atomic Spectrum When light from a heated element passes through a prism, it separates into distinct lines of color separated by dark areas called an atomic spectrum. Each element has its own unique atomic spectrum. In an atomic spectrum, light from a heated element separates into distinct lines. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. The Bohr Model (1913) Proposed by Danish physicist Niels Bohr Problems with Rutherford’s model as conflicted with laws of physics Bohr proposed new laws were needed for tiny particles like electrons led to development of quantum physics Bohr’s model solved some of these problems Main ideas electrons can only have certain allowable energies, which correspond to different distances from the nucleus = Energy Levels 74 © 2013 Pearson Education, Inc. Chapter 3, Section 1 The Bohr Model (1913) Energy levels radiate away from nucleus Energy levels are labeled by what is called the principal quantum number “n” Each holds a distinct number of electrons which corresponds to 2n2 n = 1 holds 2(1)2 = 2 electrons n = 2 holds 2(2)2 = 8 electrons n = 3 holds 2(3)2 = 18 electrons 75 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Electron Energy Levels The lines in an atomic spectrum are associated with the changes in energies of the electrons. In an atom, each electron has a specific energy, known as its energy level, which • is assigned principal quantum numbers (n) = (n = 1, n = 2, …). • increases in energy as the value of n increases and electrons are farther away from the nucleus. The energy of an electron is quantized—electrons can have only specific energy values. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electromagnetic Spectrum The electromagnetic spectrum shows the arrangement of wavelengths of electromagnetic radiation, with the visible range from 700 to 400 nm. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electrons and Energy Levels • Electrons with the same energy are grouped in the same energy level. • Energy levels are assigned values called principal quantum numbers (n), (n = 1, n = 2, …). An electron can have only the energy of one of the energy levels in an atom. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Changes in Electron Energy Level • Electrons move to a higher energy level when they absorb energy. • When electrons fall back to a lower energy level, light is emitted. • The energy emitted or absorbed is equal to the differences between the two energy levels. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. The Bohr Model (1913) 80 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Problem with Bohr Model Only worked for H atom Historically important model because: it was the first to say different laws of physics needed led to development of quantum theory, or quantum physics It was the first to suggest that electrons can only have certain, allowable energies (energy of the electron is quantized) Still use energy levels today 81 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Modern Atomic Theory Based on Quantum Physics (developed in the 1920s) Treats the electron as both a particle and a standing wave (yikes!, what does that mean?) the electron can have only certain allowable energies (e- energy is quantized) which correspond to different distances from the nucleus = energy levels Solutions to the math equations of quantum physics provide the most probable region around the nucleus of finding an electron. These “probability regions” are also known as orbitals © 2013 Pearson Education, Inc. Chapter 3, Section 1 82 Modern Model of the Atom Called electron cloud model Today, we can see the surfaces of atoms Device used is based on the wave properties of electrons (electron microscopes based on the wave properties of electrons, have very tiny wavelength, so can see very tiny things) © 2013 Pearson Education, Inc. Images of nickel atoms are produced when nickel is magnified millions of times by a scanning tunneling microscope (STM). This instrument generates an image of the atomic structure. Chapter 3, Section 3 83 Models of the Atom Between 1808 and Now 84 © 2013 Pearson Education, Inc. Chapter 3, Section 1 Energy Sublevels and The Quantum Mechanical Model The result of the quantum mechanical model (a mathematical model) is that energy levels are split into sublevels. It is the arrangement of electrons that determines the physical and chemical properties of an element. • Each energy level consists of one or more sublevels. • The number of sublevels in an energy level is equal to the principal quantum number n of that energy level. • The sublevels are identified as s, p, d, and f. • The order of sublevels in an energy level is s<p<d<f General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Sublevels General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. s Orbitals The location of an electron is described in terms of probability. • Orbitals are a threedimensional volume in which electrons have the highest probability of being found. • The s orbitals are shown as spheres. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake (a) The electron cloud of an s orbital represents the highest probability of finding an s electron. (b) The s orbitals are shown as spheres. The sizes of the s orbitals increase because they contain electrons at higher energy levels. © 2016 Pearson Education, Inc. p Orbitals There are three p orbitals, starting with n = 2. • Each p orbital has two lobes, like a balloon tied in the middle, and can hold a maximum of two electrons. • The three p orbitals are arranged perpendicular to each other along the x, y, and z axes around the nucleus. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. p Orbitals A p orbital has two regions of high probability, which gives a “dumbbell” shape. (a) Each p orbital is aligned along a different axis from the other p orbitals. (b) All three p orbitals are shown around the nucleus. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. d Orbitals Each of the d sublevels contains five d orbitals. Four of the five d orbitals consist of four lobes that are aligned along or between different axes. One d orbital consists of two lobes and a doughnutshaped ring around its center. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Orbital Capacity and Electron Spin The Pauli exclusion principle states that • each orbital can hold a maximum of two electrons. • electrons in the same orbital repel each other. • electrons in the same orbital must have their magnetic spins cancel (they must spin in opposite directions). We can represent magnetic spins with an arrow An orbital can hold up to two electrons with opposite spins. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Number of Electrons in Sublevels There is a maximum number of electrons that can fill each sublevel. • Each s sublevel has one orbital and can hold a maximum of two electrons. • Each p sublevel has three orbitals and can hold a maximum of six electrons. • Each d sublevel has five orbitals and can hold a maximum of 10 electrons. • Each f sublevel can has 7 orbitals and can hold a maximum of 14 electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Number of Electrons in Sublevels General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Which of the following elements are likely to have electrons in the 3p sublevel? C Si O As General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.7 Electron Configurations Electron configurations follow the order of occupied sublevels on the periodic table. Learning Goal Draw the orbital diagram and write the electron configuration for an element. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Orbital Diagrams Orbital diagrams use boxes to show how electrons • are arranged in the orbitals of an atom. • fill the orbitals and energy levels from lowest to highest energy level. • fill orbitals within the same sublevel one at a time, before pairing the electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electron Configurations Chemists use a notation called electron configuration to • indicate the placement of electrons in an atom. • show how electrons fill energy levels and sublevels in order of increasing energy. • write an abbreviated form using a noble gas to represent all electrons preceding it. Electron Configuration for Carbon Core Chemistry Skill Writing Electron Configurations General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Period 1: Hydrogen and Helium General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Period 2: Lithium to Neon General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Drawing Orbital Diagrams General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Drawing Orbital Diagrams Nitrogen atoms are found in amino acids, proteins, and nucleic acids. Draw the orbital diagram for nitrogen. STEP 1 Draw boxes to represent the occupied orbitals. Nitrogen’s atomic number is 7, which means it has seven electrons. For the orbital diagram, we draw boxes to represent the 1s, 2s, and 2p orbitals. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Drawing Orbital Diagrams Nitrogen atoms are found in amino acids, proteins, and nucleic acids. Draw the orbital diagram for nitrogen. STEP 2 Place a pair of electrons with opposite spins in each filled orbital. First we place a pair of electrons with opposite spins in the1s and 2s orbitals. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Drawing Orbital Diagrams Nitrogen atoms are found in amino acids, proteins, and nucleic acids. Draw the orbital diagram for nitrogen. STEP 3 Place the remaining electrons in the last occupied sublevel in separate orbitals. Place three remaining electrons in the three separate 2p orbitals, with arrows drawn in the same direction. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Period 3: Sodium to Argon General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electron Configurations and the Periodic Table The electron configurations of elements are related to their positions on the periodic table. Different sections or blocks correspond to sublevels s, p, d, and f. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Blocks on the Periodic Table 1. The s block contains elements in Groups 1A (1) and 2A (2). This means the final one or two electrons are in the s sublevel. 2. The p block consists of elements in Group 3A (13) to Group 8A (18). There are six p block elements in each period, because three p orbitals can hold a maximum of six electrons. 3. The d block, which contains transition elements, first appears after calcium (atomic number 20). There are 10 elements in the d block, because five d orbitals can hold a maximum of 10 electrons. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Blocks on the Periodic Table 4. The f block, the inner transition elements, is the two rows of elements at the bottom of the periodic table. There are 14 elements in each f block, because seven f orbitals can hold a maximum of 14 electrons. Core Chemistry Skill Using the Periodic Table to Write Electron Configurations General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Writing Configurations Using Sublevel Blocks Use the sublevel blocks on the periodic table to write the electron configuration for chlorine. STEP 1 Locate the element on the periodic table. Chlorine (atomic number 17) is in Group 7A (17) and Period 3. STEP 2 Write the filled sublevels in order, going across each period. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Guide to Writing Configurations Using Sublevel Blocks Use the sublevel blocks on the periodic table to write the electron configuration for chlorine. STEP 3 Complete the configuration by counting the electrons in the last occupied sublevel block. Because chlorine is the fifth element in the 3p block, there are five electrons in the 3p sublevel. The electron configuration for chlorine (Cl) is 1s22s22p63s23p5. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electron Configurations: Period 4 and Above Beginning in Period 4, • the 4s sublevel fills before the 3d sublevel, because the 3d sublevel is slightly lower in energy than the 4s sublevel. • the 5s sublevel fills before the 4d sublevel. • the 6s sublevel fills before the 5d sublevel. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electron Configurations: Period 4 and Above General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Electron Configurations: Period 4 and Above General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Use the sublevel blocks on the periodic table to write the electron configuration for selenium. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Use the sublevel blocks on the periodic table to write the electron configuration for selenium. STEP 1 Locate the element on the periodic table. Selenium is in Period 4, Group 6A (16). STEP 2 Write the filled sublevels in order, going across each period. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Use the sublevel blocks on the periodic table to write the electron configuration for selenium. STEP 3 Complete the configuration by counting the electrons in the last occupied sublevel block. Because selenium is the fourth element in the 4p block, there are four electrons to place in the 4p sublevel. The electron configuration for selenium (Se) is 1s22s22p63s23p64s23d104p4. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 3d Sublevel Exceptions • For chromium (Cr), moving one of the 4s electrons to the 3d sublevel adds stability with a half-filled d subshell, and the resulting configuration is 4s13d5. • For copper (Cu), moving one of the 4s electrons to the 3d sublevel adds stability with a filled d subshell, and the resulting configuration is 4s13d10. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Use the periodic table to give the symbol and name for the element with the electron configuration of 1s22s22p63s23p64s23d7. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Use the periodic table to give the symbol and name for the element with the electron configuration of 1s22s22p63s23p64s23d7. There are seven electrons in the 3d sublevel. Thus, the element is cobalt (Co). 1 2 3 Sc Ti V 4 5 6 7 Cr Mn Fe Co Ni General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake Cu Zn © 2016 Pearson Education, Inc. Study Check Write the electron arrangement for the following elements: C Si O General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution STEP 1 Locate the element on the periodic table. C: atomic number 6, Period 2, Group 4A (14) Si: atomic number 14, Period 3, Group 5A (15) O: atomic number 8, Period 2, Group 6A (16) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution STEP 2 Write the filled sublevels in order, going across each period. C 1s22s2 Si 1s22s22p63s2 O 1s22s2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution STEP 3 Complete the configuration by counting the electrons in the last occupied sublevel block. C, the second element in the 2p block, has two electrons to place in the 2p sublevel: 1s22s22p2. Si, the second element in the 3p block, has two electrons to place in the 3p sublevel: 1s22s22p63s23p2. O, the fourth element in the 2p block, has four electrons to place in the 2p sublevel: 1s22s22p4. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. 4.8 Trends in Periodic Properties The atomic size of representative elements is affected by the attractive forces between the protons in the nucleus and the electrons in the outermost energy level. Learning Goal Use the electron configurations of elements to explain the trends in periodic properties. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Group Numbers: Valence Electrons • For representative elements in Groups 1A (1)–8A (18), chemical properties are due to the number of valence electrons. • Valence electrons are the number of electrons in the outermost energy level. • The group number gives the number of valence electrons for the representative elements. Core Chemistry Skill Identifying Trends in Periodic Properties General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Valence Electron Configurations Valence Electron Configuration for Representative Elements in Periods 1 to 4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Using the periodic table, write the group number, the period, and the valence electron configuration for the following: A. calcium B. lead General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution The valence electrons are the outermost s and p electrons. Although they may have electrons in the d or f sublevel, they are not valence electrons. A. Calcium is in Group 2A (2), Period 4. It has a valence electron configuration of 4s2. B. Lead is in Group 4A (14), Period 6. It has a valence electron configuration of 6s26p2. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Lewis Symbols Lewis symbols represent the valence electrons as dots placed on sides of the symbol for an element. • One to four valence electrons are arranged as single dots. • Five to eight valence electrons are arranged with at least one pair of electrons around the symbol for the element. Lewis Symbols for Magnesium Core Chemistry Skill Drawing Lewis Symbols General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Lewis Symbols Lewis Symbols for Selected Elements in Periods 1 to 4 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Write the electron-dot symbol for each of the following elements: Cl, C, N. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Solution Write the electron-dot symbol for each of the following elements: Cl, C, N. Cl General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake C N © 2016 Pearson Education, Inc. Atomic Size Atomic size • is determined by the atom’s atomic radius, the distance between the nucleus and the outermost electrons. • increases for representative elements from top to bottom of the periodic table. • decreases within a period as a result of increased number of protons in the nucleus. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Atomic Size For representative elements, the atomic size increases going down a group but decreases going from left to right across a period. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Ionization Energy Ionization energy is the energy required to remove one of the outermost electrons. Na(g) + energy (ionization) Na+(g) + e− • As the distance from the nucleus to the valence electrons increases, the ionization energy decreases. • The ionization energy is low for metals and high for the nonmetals. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Ionization Energy Ionization energy decreases down a group and increases going across a period from left to right. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Metallic Character An element with metallic character is one that loses valence electrons easily. Metallic character • is more prevalent in metals on the left side of the periodic table. • is less for nonmetals on the right side of the periodic table that do not lose electrons easily. • decreases going down a group, as electrons are farther away from the nucleus. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Metallic Character The metallic character of the representative elements increases going down a group and decreases going from left to right across a period. General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Summary of Trends in the Periodic Table General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc. Study Check Given the elements C, N, and Cl, A. which is the largest atom? B. which has the highest ionization energy? C. which belongs to Group 5A (15)? General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C. Timberlake © 2016 Pearson Education, Inc.