Diatomic molecules bond energies

The bond enthalpies for diatomic molecules are:

C-C 347 kJ/mol

C-N 276 kJ/mol

C-O 351 kJ/mol



Why is carbon-nitrogen bond enthalpy lower? What factor makes that?



And also the halogens bond enthalpies:

F-F 157 kJ/mol

Cl-Cl 243 kJ/mol

Br-Br 193 kJ/mol

I-I 151 kJ/mol



Why has fluorine lower enthalpy? I suppose a polarizability plays a role - iodine is highly polarizable, so when approaching two atoms of iodine, they make large dipoles so they do great work... or something like that. Is it true?