Question

How do you draw the Lewis dot structure for `KNO_3`?

Answer 1

Well, you gots a potassium cation, and nitrate anion as the gegenion..

Explanation:

Nitrate anion is an interesting customer in terms of resonance, in that THREE of the FOUR atoms bear a formal electric charge in the resonance structure. And of course the charges SUM to the formal charge of nitrate anion, i.e. negative ONE...

And so for `NO_3^(-)`...we add up the valence electrons, i.e. `5_"nitrogen electrons"+3xx6_"oxygen electrons"+1_"negative charge"=24*"electrons".`

And so we gots 12 electron pairs to distribute over four centres...nitrogen as the least electronegative atom is the CENTRAL atom: `:stackrel(ddot)O=stackrel(+)N(-O^(-))_2`...the which structure distributes the 12 electron pairs as required. The nitrogen atom in nitrate is FORMALLY QUATERNIZED, and bears a formal positive charge. Of course, all the oxygen atoms are equivalent, as resonance would suggest.

As written nitrate has a formal NEGATIVE charge..as the Lewis structure indicates, and neutrality for THE SALT is obtained with the potassium cation, `K^+`..

Can you do the same thing for `"nitrite anion,"` `NO_2^(-)`? What about for `NO_2`, a NEUTRAL gas?