Question

In the periodic table of the elements, only a few of the elements are gases at standard temperature and pressure. Those elements include the noble gases some of the halogens, and a few of the elements next to them, i.e. oxygen and nitrogen.

So why are these elements gases?

Answer 1

The lighter halogens are quite eager to form covalent bounds and become diatomic molecules. These are strongly bound. Because charge is distributed symmetrically among these bounds, the resulting molecules are not strongly polarized, so the interaction with other molecules is relatively weak. Therefore, you neither have solids nor liquids with them.

Light halogens are the most electronegative elements in the periodic table en.wikipedia.org/wiki/Electronegativity so their bonds are among the strongest ones the elements may exhibit. That's why they instantly form the diatomic molecules, and . After all, the same is true for nitrogen and oxygen next to fluor in the periodic table, too. The resulting diatomic molecules are symmetric and still "electronegative", i.e. "thirsty to steal e-", but in the fluor or chlor gas, there is no one who could donate electrons so the molecules don't grow and don't interact with each other.