1.9 Sulfur

Sulfur sits directly below oxygen on the periodic table - we can say it is a congener of oxygen - and like oxygen, it is (often) divalent. Its atoms are too big to form diatomic molecules, so it is solid. H₂S is hydrogen sulfide, or rotten egg gas, and it is a heavier analogue of water. (In section 5 we'll see why it is a gas when it's heavier than a liquid.) Divalent sulfur is not tetrahedral like oxygen is; its bonds are at 90° angles, and the repulsion between the two hydrogens in H₂S bend the angle to about 96°.

Sulfur has other compounds where its valence is 4 or 6. Sulfur dioxide or SO₂ is not linear like carbon dioxide; it has a bent O=S=O molecular structure. Sulfuric acid or H₂SO₄ has both single and double bonds between the sulfur and the oxygens, and it happens to be tetrahedral:

Sulfur and oxygen are part of the series of elements called chalcogens, along with selenium, tellurium, and polonium.

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