Sulfur dioxide

Sulfur dioxide (also sulphur dioxide) is the chemical compound with the formula SO
2. At standard atmosphere, it is a toxic gas with a pungent, irritating, and rotten smell. The triple point is 197.69 K and 1.67 kPa. It is released naturally by volcanic activity.

Sulfur dioxide was used by the Romans in winemaking when they discovered that burning sulfur candles inside empty wine vessels kept them fresh and free from vinegar smell.

Structure and bonding

SO₂ is a bent molecule with C_2vsymmetry point group. A valence bond theory approach considering just s and p orbitals would describe the bonding in terms of resonance between two resonance structures.

The sulfur–oxygen bond has a bond order of 1.5. There is support for this simple approach that does not invoke d orbital participation. In terms of electron-counting formalism, the sulfur atom has an oxidation state of +4 and a formal charge of +1.

Occurrence

It is found on Earth and exists in very small concentrations and in the atmosphere at about 1 ppb.