Chem 113 Jan 29 cont. 1/29/09 10:32 AM Ernest Rutherford (1910) Alpha particle scattering expert. Proved the existence of a dense nucleus and also disproved Thompson?s ?Plum Pudding? model. Gold foil experiment (1919) Discovered the proton James Chadwick (1932) Discovered the neutron Elementary Particles: Structure of the Atom Mostly empty space Dense nucleus surrounded by e- Nucleus contains all p+ and n^o Atomic & Mass Number A ------Mass # (p+ + n^o) E -------Element Symbol Z --------Atomic # (p+) Top number is needed to show what isotope it is. Bottom number is what it is on the periodic table. Top number ? bottom number = n^o Isotopes can be: Stable Radioactive Naturally occurring Anthropogic (man made) Isotopes written as: Carbon-12 or C-12 (6p+, 6n^o, 6e-) Carbon-13 or C-13 (6p+, 7n^o, 6e-) Atomic mass on the periodic table - is the mass of each naturally occurring isotopes multiplied by its % natural occurrence Atomic mass of Cl = 34.96885g(0.7578) + 36.96590g(0.2422) = 35.45g Chem 113 Jan 29th 1/29/09 10:32 AM The Periodic Table 117 known elements 94 occuring naturally on earth 95 detected in universe elements above #94 are non metal and radioactive Medeleev Determined that element properties recur in cycles when arranged by increasing atomic mass ?Law of Mendel? or ?Chemical Periodicity? Layout Elements listed by atomic #, symbol, and atomic weight Colums ? up or down: have own number Na = group 1A O = group 6A Rows (period) ? left/right + sections Three main categories 1. Representative (main group) Elements group 1A, 2A, 3A-8A most of early chem. Was based on these Show the strongest trends each 8 elements 2. Transition Metals group 3B-8B (middle) 3. Lanthanides and actinides labeled at the bottom might be named inner transition metals follow La and Ac, hence the names Types and locations Group 1A: Alkali metals Group 2A: Alkali Earth metals Group 8A: Noble gases Stair step region: Metalloids Left of metalloids: Metals Right of metalloids: Nonmetals Group 6: Chalcogens Group 7: Halogens Basic Properties Metals Shiny Ductile (stretch into wire) Malleable (hammered into sheets) Good conductors of heat and electricity High density High melting point Nonmetals Dull Poor conducts (insulators) Brittle Low density Low melting point Metalloids Solid at room temp Shiny or dull Ductile and malleable or brittle Semi-Conductivity (less than metals more than nonmetals) Noble Gases Very Nonreactive Particle Symbol Actual Charge Relative Charge Proton P+ +1 1.0073 Neutron N^o 0 1.0087 Electron e- -1 5.486*10^-4
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