Nickel has 28 electrons, its electron configuration is:
[tex]1s^22s^22p^63s^23p^64s^23d^8[/tex]Ni2+ has lost 2 electrons, which means that the resulting configuration would be:
[tex]1s^22s^22p^63s^23p^64s^23d^6[/tex]Nevertheless, since 4s electrons are further from the nucleus, they are lost resulting in a more stable ion, then, the actual configuration of Ni2+ is:
[tex]1s^22s^22p^63s^23p^63d^8[/tex]It means that this ion has 16 valence electrons.
