Why is the melting point of nitrogen ($\ce{N2}$) greater than that of oxygen ($\ce{O2}$)? After all, both are non-polar, and $\ce{O2}$ has more electrons than $\ce{N2}$.
In addition, why is the boiling point of both opposite? I mean, why is the boiling point of oxygen greater than that of nitrogen, even though the melting point of nitrogen is greater than that of oxygen?