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Unformatted text preview: Chapter 8 Notes from Prof- Chemical Bond Formation (Ch 8.1) Ionic Bonds : one or more valence electrons is transferred from one atom to another Form cation and anion (coulomb attraction) Covalent Bonds: sharing of one or more valence electrons between atoms e.g. H. + H. HH - Valence Electrons and Lewis Dot Structure (Ch 8.2) Bonding and chemical reactions involve valence electrons; core electrons are unimportant. Why are core electrons unimportant? 1. Core electrons are extremely tightly bound 2. Very close to nucleus Lewis Electron Dot Symbols-way to represent valence electrons of an atom (useful only for main group elements). [noble gas](ns^x)(np^y) 1 x + y 8 (And (n-1)d^10) 4 8 5Atom 3 1 6 2 7 Lewis Dot Structures Bonds are formed when one or more electron pairs are shared between atoms. Multiple bonds: two or more electron pairs are shared. Note: for main group compounds, 8 electrons typically surround each atom =octet rule e.g. 1. Methane CH4 4 x HC single bonds 2. Ethylene 4 x H (1 dot) ; 2 x C (4 dots) 4 HC bonds (2 per C atom) (C is connected by a double bond) 3. HCN H (1 dot) ; C (4 dots) ; N (5 dots) 1 HC bond- Isoelectronic Species Same number of valence electrons Same Lewis structures e.g. N= N C= O [C= N]- 111.2pm 112.8pm 115.3pm (in HCN)- Formal Atomic Charges Formal charge = (number of valence electrons) (LPE + 1/2BP) Number of valence electrons = group number of atom LPE = lone pairs of electrons BP = bonded pairs of electrons e.g. Methane H H = 1-(0+1/2(2)) = 0 H-C-H C = 4-(0+1/2(8)) = 0 H Covalent limit (Lewis structures) C= O C = 4-(2+1/2(6)) = -1 O = 6-(2+1/2(6) = 1 Ionic limit is with the dots and sharing of electrons < 8 valence electrons...
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