The formal charges on the atoms marked as (1) to (4) in the Lewis representation of HNO3 molecule respectively are [figure]
- 0, 0, -1, +1
- 0, -1, 0, +1
- 0, +1, 0, -1
- +1, 0, 0, -1
Answer
(3) 0, +1, 0, -1
Solution
Formal charge (F.C.) = V - L - 12S, where V = valence electrons, L = non-bonding electrons and S = bonding electrons.
Atom (1) is O bonded to H and N (2 bonds, 2 lone pairs), so F.C. = 6 - 4 - 12(4) = 0.
Atom (2) is N with one double and two single bonds and no lone pair, so F.C. = 5 - 0 - 12(8) = +1.
Atom (3) is O doubly bonded to N (2 lone pairs), so F.C. = 6 - 4 - 12(4) = 0.
Atom (4) is O singly bonded to N (3 lone pairs), so F.C. = 6 - 6 - 12(2) = -1.
Formal charges on (1) to (4) are 0, +1, 0, -1.
Answer: (3)