This leaves two nonbonding pairs on each of the outer atoms. The bond orders are therefore both 2. In all resonance structures, the central N atom has no nonbonding pairs. A linear geometry minimizes the repulsion between the bonding electrons. If an electron is promoted from the 2s subshell to an empty 2p orbital, boron obtains three half-filled orbitals which can then be used in bonding.
Xenon has eight valence electrons.
With a filled octet, it can't form covalent bonds without valence shell expansion. However, if we take one electron from the 5p subshell and promote it to the 6s orbital, xenon becomes capable of forming the two bonds needed to form . Selenium is in group 16 so it has six valence electrons. If it shares four of these electrons with the four fluorine atoms, it has one pair of electrons left over. The Lewis diagram is therefore There are five electron pairs around the selenium atom.