Question

Why is dioxygen a gas but sulfur a solid?

Answer 1

Oxygen has the weak Van Der Waals forces (attraction or repulsion between / molecules) as an intermolecular force whereas sulfur has 8S atoms linked by S-S bonds and it is strongly held together by a covalent bond (a molecular bond and a chemical bond includes sharing of electron pairs between atoms).

Complete step by step answer: Oxygen is existing as gas because it is smaller in size as compared to sulfur. It can effectively form $p\pi$-$p\pi$ bonds due to its smaller size. It forms ${O_2}\left( {O = O} \right)$molecule. But sulfur exists as a tightly gathered(puckered) like structure and large in size which can’t form $p\pi$-$p\pi$ bonds. It is linked together by strong covalent bonds. It forms ${S_8}$ Structure in order to gain stability and does not form S=S double bond. Hence, it exists as a solid.
Oxygen molecules are held together by weak Vander Waals force of attraction. This force of attraction is overcome by the collisions of molecules at room temperature. It is a high electronegativity atom. While sulfur is a low electronegativity atom. It has a high tendency of catenation and also forms octa-atomic molecules. The sulfur molecules are linked together by a strong force of attraction. Oxygen exists as a diatomic molecule (2 atoms are chemically bonded) whereas sulfur exists as a polyatomic molecule (3 or more atoms are linked by the covalent bond).

Note: Keep in mind that sulfur does not form S=S bond instead it forms ${S_8}$ to decrease the repulsion between the atoms and which results in a smaller bond angle between the atoms.