Unformatted text preview: ).
7. Use the concept of formal charge to assess the plausibility of
the Lewis structure. Formal Charge
Formal Charge: An atom in a molecule owns its lone pairs completely, but has an equal share in bonding electron pairs.
If this results in an atom having more electrons in the molecule
than as a free, neutral atom, we say that the atom has a negative formal charge in the Lewis structure. If it has less electrons
in the molecule, then it has a positive formal charge.
FC = number of valence electrons of free atom − number of lonepair electrons − 1 number of shared electrons
The sum of formal charges must equal zero for a neutral molecule and must equal the charge for ions.
GChem I 9.10 Lewis structures with the lowest formal charges are most plausible. Exercise: Write the Lewis structure for CF2 Cl2 (Freon-12) A = number of available valence electrons
A = 4 + 2 × 7 + 2 × 7 = 32
N = number valence electrons needed for octets
N = 5 × 8 = 40
S = N − A = number of shared electrons
View Full Document