chem notes 9-14 - September 14, 2007 Dr. Stevens Gen. Chem....

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September 14, 2007 Dr. Stevens Gen. Chem. 1 Isotopes -atoms of some element with different numbers of neutrons in nucleus -always same z (atomic number) -ex: 13/6 C, 12/6 C, 14/6 C -masses on periodic table are weighted avg. of all isotopic masses -98% C-12, 17% C-14, 1% C-13 -avg. mass much closer to C-12 Chemical Properties and Reactivity -defined by number of valence e- (outside shell) -PT arranged in “groups” (vertical columns) with similar properties -group has same number of external electrons in same type of environment (orbitals) -ex: H, Li, Na, K, Rb, Cs, Fr -group 1: alkali metals (H group) -group 2: alkaline earth metals (Be group) -group 6: chalcogens (O group) -group 7: halogens (F group) -group 8: noble gases (He group) – mostly unreactive (bottom ones a bit more reactive) -left side = most reactive -> right side = least reactive -horizontal rows = periods (very little similarity in properties) -one more p+ and e- than the previous one -middle elements (transition metals) = no groups, just periods
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chem notes 9-14 - September 14, 2007 Dr. Stevens Gen. Chem....

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