Question

How can I determine the outer electron configuration of the selenide ion and its chemical formula?

Answer 1

Se is in Group VI, hence it has 6 valence electrons, and most likely will taken in 2 more electrons to gain stability with an octet. Thus ion of Se should have a charge of -2 and the electronic configuration should be 2,8,18,8.. . Hope this helps :)

Answer 2

Look at what Group it is in: 6 (in the UK) and 16 (in USA).. That means that it has 6 electrons in the outer level, and wants 8, so it will gain two to become Se2-.. The outer electron configuration of Se will be 4s2, 4p4, going up to 4p6 for the ion.