Answer
The Lewis symbol for $N^{3-}$ atom is seen in the diagram.
Work Step by Step
RULES TO WRITE LEWIS SYMBOL
- Find out the number of valence electrons in the atom.
- Write the element symbol and around it present each valence electron with one dot to the top, bottom, right or left of that symbol.
- Spread out the dots as much as possible (so there would be minimum electron-electron repulsions), and no spots can hold over 2 electrons.
1) $N$ is in group 5A, so a neutral $N$ atom has 5 electrons in the outermost occupied shell.
However, anion $N^{3-}$ added 3 more electrons to the outermost shell compared with its neutral $Sn$ atom. So, $N^{3-}$ has 8 electrons in the outermost occupied shell.
That means $N^{3-}$ has 8 valence electrons. The Lewis symbol of $N^{3-}$ would have 8 dots.
2) 8 dots is the maximum number of dots in a Lewis symbol (for now). Since each spot can hold no more than 2 dots, 8 dots would spread evenly into 4 spots, so each spot holds 2 dots.
Eventually, all 4 spots are occupied by 2 dots.
