Final answer:
Sulfur can exceed the octet rule due to the presence of accessible d orbitals in its third energy level, allowing more than eight valence electrons, leading to hypervalent molecules. Phosphorus in PCl₅ and selenium are other examples of elements that can expand their octet.
Step-by-step explanation:
Sulfur can have more than 8 valence electrons due to an effect known as valence expansion. This phenomenon is common for elements in the third period and beyond in the periodic table, such as sulfur, phosphorus, and others, which can have access to d orbitals in the same shell. Due to the presence of these d orbitals, they can have more than the traditional eight electrons in their valence shell, thus forming expanded octet or hypervalent molecules.
For example, sulfur has 12 valence electrons in the compound H₂SO₄, where it exceeds the octet rule. Two other elements that can have more than 8 valence electrons are phosphorus, as seen in phosphorous pentachloride (PCl₅) with 10 valence electrons, and selenium, which can also form hypervalent compounds similar to sulfur.