Isoelectronic species are known as atoms or ions that have the same number of electrons. In isoelectronic species, there the number of electrons would be equal but the elements would be different. In other words, ions and atoms which are having equal numbers of electrons are called the isoelectronic species.
1. Na +, F – is an isoelectronic pair and their electronic configuration is 1s2 2s2 2p6.
Fluorine ion is possessing 10 electrons (9 + 1 = 10). Hence, the species which is isoelectronic with F – must also have 10 electrons.
Na +ion it is also having 10 electrons ( 11 – 1 = 10).
2. N3-, Al3+, Mg2+, for N3- the number of electrons would be 10, that is 7 + 3.
For Al3+ would be 10, and for Mg2+ its 10.