Lewis Structure 1 - pdf

L-2 DRAWING LEWIS STRUCTURESUsually molecular structure is known. If not, choose central atom inmolecule as one requiring the largest no. of e - ‘s (in addition to thosealready in its valence shell) to achieve a noble gas (8) configuration.(H & F are never central atoms.) The following rules work well withrepresentative elements.In summary:1. A = Total no. e – ’s available in outer shells of all atoms (∑ P.G.No.). One e – must be added for each negative charge orsubtracted for each positive charge of an ion.2. N = Total no. e - ‘s needed to attain noble gas configuration for allatoms in molecule.H = 2M = 83. S = N-A = No. e – ’s shared.4. Assign 2 e – to each bond (first).5. If any e – ’s to be shared remain use them to form multiple bonds(double: C, N, O, S; triple: C, N).6. Assign remaining e – ’s as lone pairs.

L3 CH4N = 8 + 4(2) = 16HA = 4 + 4(1) = 8 H• • C ••S = 16 – 8 = 8••H••HH2ON = 2(2) + 8 = 12A = 2(1) + 6 = 8 • • O ••S = 12 – 8 = 4••H•H

L-4H C N (C = central atom)N = 2 + 8 + 8 = 18A = 1 + 4 + 5 = 10S = N - A = 18 - 10 = 181. H • • C • • N2. Need S = 8 so H • C • • • N83. Need A = 10 so H • C • • • N• •