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A Neutron walked into a bar and asked how much for a drink. The bartender replied, “for you, no charge.” -Jaime- Internet Chemistry Jokes Chapter 3 Atoms: The Building Blocks of Matter Section 1 - The Structure of the Atom -Objectives: – Define atom – List the properties of subatomic particles – Determine the number of protons, neutrons, electrons found in different elements from the periodic table What is an atom? -Atom: the smallest particle of an element that retains the chemical properties of that element -Named by Democritus -Means “indivisible” What is an atom made of? -Discoveries made by people like Dalton, Thomson, Millikan, Rutherford, and Bohr -Subatomic particles: – Protons – Neutrons – Electrons Subatomic Particles -Nucleus – Protons and neutrons – Majority of the mass – Strong nuclear force holds it together -Electron shells or orbitals – Electrons – Most of the volume Subatomic Particles -Electron: – Negative charge – Tiny, very light particles – Electron cloud -Proton: – Positive charge – At least one in every atom – Much greater in size and mass than electrons – Nucleus -Neutron: – Neutral (no) charge – About the same size and mass as protons – Nucleus How do we measure an atom’s size? -Atomic Number - #protons - Atomic Number Atomic Symbol Atomic Mass -Atomic Mass (or mass number) = #protons + #neutrons What about the electrons? -If an atom is electrically neutral, then #protons = #_________ Practice: -Determine the number of protons, neutrons, and electrons in the following neutral atoms: – Sodium – Carbon – Chlorine – Helium – Arsenic Practice: -Determine the number of protons, neutrons, and electrons in the following atoms: – – – – – Sodium (Na): p+:11 e-:11, n0:12 Carbon (C ): p+:6 e-:6, n0:6 Chlorine (Cl): p+:17 e-:17, n0:18 Helium (He): p+:2 e-:2, n0:2 Arsenic (As): p+:33 e-:33, n0:42 Isotopes -Isotopes: atoms of the same element that have different masses. – Same # of protons and electrons, but differ in # of neutrons • Different ways to depict which isotope you have: mass number (p + n) A Z atomic number (p) X element symbol Isotopes 6p+ 8nº Mass of Atoms - Mass of atom determined by protons and neutrons - Actual Mass of: - Proton: 1.673 X 10-27 kg - Neutron: 1.675 X 10-27 kg - Electron: 9.109 X 10-31 kg - Mass of oxygen-16 atom= 2.657 X10-23 g Relative Atomic Mass - Instead of using EXACT mass of an atom in kg, scientists use the relative atomic mass - Relative Atomic mass measured in atomic mass units (amu) - Proton= 1.007276 amu - Neutron= 1.008665 amu - Electron= 0.0005486 amu Calculating atomic mass • Average atomic mass = Σ (mass of isotope × relative abundance) • Carbon-12 is the isotope this formula was based upon • Ex: One type of copper atoms weighs in at 62.93 amu, the other has a mass of 64.94 amu. The lighter isotope is more common with 69.09% occurrence. Calculating atomic mass • Average atomic mass of copper = (62.93 amu × 0.6909) + (64.94 amu × 0.3091)= 63.55 A certain atom has a nucleus containing six protons and eight neutrons and has six electrons orbiting the nucleus. This atom is a form of the elementA) silicon B) carbon C) magnesium D) calcium Ch 3: Section 2 – History of Subatomic particles Objectives: 1. Identify and describe the discoveries and research of Democritus, Dalton, Rutherford, Thomson, Bohr, Mosley, Mendeleev and Schrodinger 2. Describe the law of conservation of mass and law of multiple proportions 3. Describe the atomic theory and its individual components Timeline of Events: 370 BC- Democritus - Coined term atom 1803- Dalton - Atomic Theory 1871- Mendeleev – Created periodic table 1897- Thomson - Discovered electron 1911- Rutherford - Discovered proton and nucleus 1911- Mosley- Rearranged periodic table 1915- Bohr- Discovered neutron and made Bohr model 1925- Shrodinger – Quantum theory Democritus vs. Aristotle Greek Philosophers Aristotle- viewed the entire known universe as being made up of five distinct “elements” (earth, fire, air, water, and ether) which mixed to form anything of substance Democritus asked- If you break a piece of matter in half again and again, how many breaks will you have to make before you can break it no more? Democritus thought that it ended at some point, a smallest possible bit of matter. He called these particles atoms. (370 BC) People believed Aristotle for almost 2000 years John Dalton’s Research Dalton- English chemist, meteorologist, and physicist He studied the atomic mass of elements by studying water and carbon dioxide and decided atoms are tiny, hard spheres He used ideas made by scientists before himDemocritus, Lavoisier , and Proust- to come up with his atomic theory Timeline of Events: 1803: Dalton- Created the Atomic Theory Atomic Theory: 1) All matter is composed of atoms 2) Atoms of a given element are identical in size, mass, and other properties 3) Atoms can not be subdivided, created, or destroyed ( law of conservation of mass) (Subdivided part has been disproven) 4) Atoms of different elements combine in simple wholenumber ratios to form compounds (law of multiple proportions) 5) In reactions, atoms are combined, separated, or rearranged Law of multiple proportions - Atoms of different elements combine in simple whole- number ratios to form compounds - Examples: - NaCl - H2O Law of conservation of mass Atoms can not be created or destroyed • Example: How can you explain chemical reactions? *Atoms are rearranged, separated, combined 2H2O + O2 --> 2H2O2 Dalton’s Theory update • Dalton proposed that atoms cannot be divided – Nuclear fission- a nuclear reaction in which the nucleus of an atom splits into two smaller parts, releasing tremendous amounts of energy • Nuclear power plants Dalton 1803 • Many scientists agreed on this theory and it stayed unchanged until 1890 – Scientists that followed used Dalton’s theory and expanded on it Dmitri Mendeleev (1871) • Dmitri Mendeleev – first to organize elements according to their properties and mass –Predicted the existence and properties of elements not yet discovered –Left blank spots –Father of the modern periodic table because he created the first one J.J. Thomson’s Research (1897) Discovered electron using cathode ray Thomson studied cathode rays and found that they were negatively charged because they were deflected in magnetic fields. Came up with “Plum pudding” model Henry Mosley (1911) • British Scientist 1911 • Re-ordered the periodic table in order of increasing atomic number instead of mass. • Problems with the Mendeleev table disappeared. Ernest Rutherford’s Research (1911) Discovered proton and a nucleus by hitting gold foil with helium (alpha) particles Discovered much of the atom is “empty space” He hit gold foil with fast-moving helium (alpha) particles (positively charged particles) Expected particles to pass through because the mass and charge were uniformly distributed, were deflected into all directions Concluded that a very small, dense area in the center was positively charged the rest is empty space. Gold Foil Experiment Bohr’s Research (1915) Discovered the neutron and thus was able to calculate the atomic mass Studying gamma rays pointed at hydrogencontaining compounds, found that something was in the nucleus besides protons It had no charge Created Bohr model Erwin Schrödinger (1925) • Studied electrons and their behavior • Determined electrons have dual properties • They act like matter because they have mass and volume BUT they also act like light because they can be bent or diffracted • Became known as quantum theory and helped to predict the location and shape of the electron cloud Timeline of Events: 370 BC- Democritus - Coined term atom 1803- Dalton - Atomic Theory 1871- Mendeleev – Created periodic table 1897- Thomson - Discovered electron 1911- Rutherford - Discovered proton and nucleus 1911- Mosley- Rearranged periodic table 1915- Bohr- Discovered neutron and made Bohr model 1925- Shrodinger – Quantum theory