ch2 - Chapter 2 Atoms and Elements Goals Atomic structure,...

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Unformatted text preview: Chapter 2 Atoms and Elements Goals Atomic structure, mass number, atomic number Isotopes, atomic mass from isotopic masses and abundances Mole and molar mass Elements and the Periodic Table Daltons Atomic Theory ( beginning of 19 th century ) All matter is composed of tiny, indivisible particles called All atoms of a given element are identical to each other and A chemical reaction merely involves a change in the groupings of atoms and not creation or destruction of atoms different from those of other elements Compounds consist of atoms of more than one element combined in particular ratios Law of Constant Composition: H:O Law of Multiple Proportions: CO and CO 2 Daltons Atomic Theory Building up Atomic Structure Benjamin Franklin (1706-1790) discovered two types of electricity, Joseph John Thomson discovered the electron (1896-97). Henri Becquerel discovered radioactivity in 1896. Pierre and Marie Curie continued that work: Building up Atomic Structure Robert A. Millikan (1909) determined the charge and mass of electron. Ernest Rutherford (1911-19) discovered the proton James Chadwick (1932) discovered the neutrons , Atomic Structure subatomic particles neutron : no charge, 1.0087 amu, n proton : +1 charge, 1.0073 amu, p + electron : 1 charge, 0.0005486 amu, e e distribution more diffuse The nuclear atom small, dense, central core e- distributed diffusely in space around the nucleus e n p + e Then, if radius of atom was ~ 100 m (a football stadium), the radius of the nucleus would be ~ 0.001 m = 1 mm V r 3 Then, V atom /V nucleus 10 5 . Atom is 100,000 times bigger Actual size: Radius of atom ~ 100 pm (10-10 m) Radius of nucleus ~ 0.001 pm (10-15 m) All atoms of a given element have the same number of protons Atomic number and Mass number number of protons in an atom given by total number of protons and neutrons is Atomic number and Mass number Neutral atoms have same number of protons and electrons; Atoms acquire charge by gaining or losing electrons only ( not protons!! ) Symbol X Z A n atomic number charge +, - element symbol mass number p + + n Examples Determine the numbers of electrons, protons, and neutrons in each of the following atoms/ions. Ca 40 20 Pb 209 82 2+ P 31 15 3 Isotopes atoms (of same element) that have the same number of protons but different numbers of neutrons, n A Z X i.e., different masses, A; may or may not have same number of electrons (ions) Which pairs are Isotopes? X X 5 5 2 4 5 2 2 4 X X 5 2 2 6 5 2 2 5 X X 50 24 3 52 24 3 56 26 2 56 26 X X Periodic Table a listing of the elements arranged according to their chemical and physical properties elements are arranged according to similar properties....
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ch2 - Chapter 2 Atoms and Elements Goals Atomic structure,...

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