IsoElectronic Ions

The ions having same number of electrons but different magnitude of nuclear charge are called Iso-Electron Species or Ions.

Variation of size among Iso electronic ions

With the series of Iso-electronic ions, as the nuclear charge increases, the attractive forces between electrons and nucleus also increases. This results in the decrease of Ionic radius. In other words, size of Iso electronic ions decreases with increase in the magnitude of nuclear charge.

For example, N^3–, O^2–, F^–, Na⁺, Mg ²⁺, Al³⁺ are Iso electronic ions and have 10 electrons each. The order of their size is

Al ³⁺ <  Mg ²⁺  <  Na⁺ <  F^– <   O^2–  <  N^{3 –}

Al³⁺ have highest nuclear charge of 13 units and has smallest size, whereas N^3– has lowest nuclear charges and has largest size.