Question

For a molecule of hydrazoic acid (HN3, also known as hydrogen azide), the atoms are arranged as HNNN. One resonance form of HN3 has a double bond between each of the nitrogen atoms: H−N=N=N What is the formal charge of each of the atoms in this resonance structure? Notice that the formal charges are being asked in the same order as the atoms are listed in the formula. (HNaNbNc)

Answer 1

Answer:

0; +1; -1  

Explanation:

The resonance structure of HN₃ is shown below (you can also use horizontal dashes to represent the bonding pairs).

The molecule has 16 valence electrons, and each N atom has an octet.

To get the formal charges, cut the covalent bonds in half.

Each atom gets the electrons on its side of the cut.

Formal charge = valence electrons in isolated atom - electrons on bonded atom

FC = VE - BE  

(a) On Nₐ

VE = 5

BE = 1 lone pair (2)+ 3 bonding electrons = 2 + 3 = 5

FC = 5 - 5 = 0.

(b) On Nb:

VE = 5

BE = 4 bonding electrons = 4  

FC = 5 - 4 = +1

(c) On Nc:

VE = 6

BE = 2 lone pairs(4) + 2 bonding electrons = 4 + 2 = 6

FC = 5 - 6 = -1