Question

There are many compounds composed of nitrogen and oxygen. Compare the formulas for nitrogen monoxide and nitrogen dioxide.

Answer 1

Short answer
- Nitrogen monoxide: NO
- Nitrogen dioxide: NO2

Key differences

- Composition and formula:
- NO contains one N and one O atom.
- NO2 contains one N and two O atoms.

- Oxidation states:
- In NO, N is formally +2 (O is −2).
- In NO2, N is formally +4 (each O is −2).

- Electronic structure and bonding:
- NO has 11 valence electrons, is a radical with one unpaired electron, and a bond order ≈ 2.5 (diatomic, effectively linear).
- NO2 has 17 valence electrons, is also a radical with one unpaired electron, has resonance between structures with one N=O and one N–O, giving an average N–O bond order ≈ 1.5; the molecule is bent (O–N–O angle ≈ 134°).

- Physical properties:
- NO is a colorless gas at room temperature.
- NO2 is a brown, toxic gas; it dimerizes at low temperature to N2O4 (colorless).

- Molar mass:
- NO ≈ 30.01 g·mol−1
- NO2 ≈ 46.01 g·mol−1

- Reactivity and significance:
- NO is less oxidizing, is an important biological signaling molecule (nitric oxide), and is formed in combustion and lightning.
- NO2 is a strong oxidant and an air pollutant (contributor to smog and acid rain); NO oxidizes in air to form NO2 (2 NO + O2 → 2 NO2).

If you want, I can show Lewis/resonance structures or energy/bonding diagrams for each.