Number of protons in the atomic nucleus. The total number of electrons and neutons 2. Its outermost energy shell must be filled with electrons. The number of electrons must equal the number of protons. Sharing of electron pairs is necessary.
Ionization is required.
It must be inert. An atom of nitrogen attracts electrons more strongly than an atom of hydrogen. The nitrogen is more slightly positive. The nitrogen is strongly negative. The hydrogens are more slightly positive.