The number of bent-shaped molecule/s from the following is __________
N₃⁻, NO₂⁻, I₃⁻, O₃, SO₂

Solution

Chemistry ma’am · 3 steps

Bent needs two bonds and one or two lone pairs on the centre; three lone pairs make it linear again.

1. Look at the centre. Shape depends on the electron domains around the central atom. Count the bonded atoms (a double bond counts as one domain) and the lone pairs on that atom.
2. Where lone pairs sit. With 2 bonds and 1 lone pair (3 domains), the lone pair pushes the bonds together and the molecule is bent. With 2 bonds and 3 lone pairs (5 domains), the lone pairs take the three equatorial positions of a trigonal bipyramid. The two bonds end up opposite each other, so the molecule is linear.

   Species	Bonds on centre	Lone pairs on centre	Shape
   N₃⁻	2	0	linear
   NO₂⁻	2	1	bent
   I₃⁻	2	3	linear
   O₃	2	1	bent
   SO₂	2	1	bent

3. So. NO₂⁻, O₃ and SO₂ are bent, so the count is 3.

The common slip: 4. Counting I₃⁻ as bent because its central iodine carries lone pairs gives 4. Its three lone pairs sit in the equatorial plane, so the I–I–I line stays straight.

The idea to keep. Two bonds on the centre is not enough to decide the shape. Count the lone pairs too: 0 or 3 lone pairs give a straight line, and 1 or 2 lone pairs give a bent shape.

Answer from the NTA final answer key. Solution by PrepWiser.