Ch. 4 - Atomic Structure 1

Democritus’s Atomic Philosophy Greek philosopher, first to propose idea of atoms a tomos – “un cuttable” Failed theory: Lacked experimental support Couldn’t explain chemical behavior Democritus (400 BC) 2

Defining the Atom Atom The smallest particle of an element that retains the chemical identity of that element (pg. 101) 3

Law of Conservation of Matter (Antoine Lavoisier) Law of Constant Composition (Joseph Proust) Elements combine in whole-number ratios to form compounds. e.g., water (H2O) is always 2 hydrogen to 1 oxygen Btw, by early 1800’s, there was no connection between elements and atoms; all atoms were assumed to be identical. 4

Dalton’s Atomic Theory Jons Jakob Berzelius (1799 -1848) Swedish chemist who invented modern chemical symbols. Berzelius discovered the elements silicon, selenium, cerium, and thorium. John Dalton 1803 5

Dalton’s Atomic Theory 1. All matter (elements) is composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical – but different from those of another element. 3. Atoms of different elements can physically mix, or combine in whole-number ratios to form compounds 4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed. 6

Dalton’s Atomic Theory Atoms of Element A Atoms of Element B PHYSICALLY mixed CHEMICALLY combined Fig. 4.2, pg. 102 7

Avg. atomic radius = 5×10-11 m – 2×10-10 m Sizing Up the Atom Scanning Tunneling Microscope (STM) “Nanotechnology” Instrument used to “see” atoms Avg. atomic radius = 5×10-11 m – 2×10-10 m 8

Kanji characters for atom, “original child.” 4.1 Homework #1, 2, 4 – 7 4.2 Homework #8, 9

Ch. 4 Atomic Structure 4.2 The Nuclear Atom pgs. 104 - 108 10

Subatomic Particles Atoms are divisible. 3 subatomic particles Proton, p+ Electron, e- Neutron, no 11

Subatomic Particles J.J. Thomson “Found” the electron, a negatively charged particle with very small mass. Cathode-ray tube, 1897 12

Deflected Cathode-ray Movie!! 13

Thomson’s “Plum-Pudding” Model 14

The Atomic Nucleus Ernest Rutherford “Discovered” atomic nucleus, tiny central core of an atom Gold-foil experiment, 1911 15

Rutherford’s Gold-foil exp. Movie!! 16

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The Nuclear Atom 18

The nucleus of the atom is much smaller than the atom yet contains most of its mass. 19

Ch. 4 Atomic Structure 4.3 Distinguishing Among Atoms pgs.110 - 119 20

Periodic Table Intro 21

Family Periodic Table Intro Period 22

Periodic Table Intro Alkali Metals Family Family (or group) – vertical column; elements within a family share similar chemical properties. Period – horizontal row; Alkali Metals Family 23

Atomic Number the number of protons in the nucleus of an atom. Each element has a unique number of protons. For neutral atom, the number of protons equals the number of electrons. 24

Mass Number the total number of protons plus neutrons. For neutral atom, the number of protons equals the number of electrons. e- mass not included; negligible. 25

Chemical Symbols (pg. 161) LARGER # smaller # 26

Ion – lose electron(s) a charged atom or group of atoms. formed when atoms gain or lose electrons. Cation – positive ion; p+ > e- – lose electron(s) Anion – negative ion; p+ < e- – gain electron(s) CA ION 27

Isotopes atoms that have the same atomic number but different mass numbers; same number of protons, but different number of neutrons. 28

Atomic Mass a weighted average mass of all naturally occurring isotopes; determined from mass and relative abundance for each isotope. Average Atomic Mass = (massisotope 1 × rel. abundanceisotope 1) + (massisotope 2 × rel. abundanceisotope 2) + … 29