I know hydrogen forms a diatomic molecule $\ce{H2}$, where the electronic configuration of Hydrogen is $\ce{1s}$.

But why doesn't lithium also form a diatomic molecule? Its electronic structure is $\ce{1s^2 2s}$, so can't two lithium atoms come together, share their outer electron and form $\ce{Li2}$? Same with $\ce{Na}$, $\ce{K}$ etc.

Am I missing something obvious?