Why is the covalent triple bond in diatomic nitrogen so strong? Why is it that this covalent bond is so strong when covalent bonds usually are week?

Are covalent bonds usually weak?

 

Also, Nitrogen is a diatomic molecule; how many bonds does each nitrogen atom have in a nitrogen molecule?

The nitrogen molecule has a perfect configuration of molecular orbitals for all its electrons. That makes the molecule very stable, unreactive, good insulator and so on.

 

Each nitrogen atom has three 2p electrons, making six for the pair of atoms.

Atoms have three 2p orbitals; two atoms close to an other make six molecular orbitals resulting from atomic 2p:

- Three such orbitals are bonding, with favourable energy;

- The three others are antibonding (they're better for an electron than far from the nucleus, but less so than at the 2p of a lone atom).

- Each orbital can accept two electrons of opposite spin, so the bonding molecular orbitals take six electrons: perfect.

 

If you compare with the oxygen molecule: it has 2*4 electrons to put on the molecular orbitals resulting from 2p, but only six places are on bonding orbitals, so two electrons must go to antibonding ones. These electrons are less bonded to the molecule and ready to react.

 

You can search for "singlet oxygen" for more funny observations and explanations.