Why is nitrogen a gas and phosphorous is a solid at room temperature?

Answer 1

Nitrogen forms molecules N2, whereas phosphorus forms larger molecules such as P4.(Phosphorus has a number of allotropes). The underlying reason is that nitrogen a second period element can form double bonds to itself much better than P which is in period 3.

Answer 2

Nitrogen is a gas at room temperature because nitrogen molecules are diatomic (N2), which results in weak intermolecular forces. Phosphorus is a solid at room temperature because it exists as a molecular solid with strong covalent bonds between phosphorus atoms.