Step 1. Count the total number of valence electrons of the nitrogen atom, the oxygen atoms and the additional one negative charge (equal to one electron).
`N(2s^(2) 2p^(3)), O (2s^(2) 2p^(4))`
5 + (2 × 6) +1 = 18 electrons ltbvrgt Step 2. The skeletal structure of `NO_(2) ^(-)` is written as : O N O
Step 3. Draw a single bond (one shared electron pair) between the nitrogen and each of the oxygen atoms completing the octets on oxygen atoms. This, however, does not complete the octet on nitrogen if the remaining two electrons constitute lone pair on it
`[:underset(..)overset (..)O" " :overset(..)N:" " overset(..)underset(..)O:]^(-)`
Hence we have to resort to multiple bonding between nitrogen and one of the oxygen atoms (in this case a double bond). This leads to the following Lewis dot structures.
`[:underset(..)overset (..)O" " :overset(..)N:" " overset(..)underset(..)O:]^(-)`
or `[underset(..)overset(..)O=overset(..)N-overset(..)underset(..)O:]^(-)" or " [:underset(..)overset(..)O-overset(..)N=overset(..)underset(..)O]^(-)`
