Isoelectronic - Definition and Overview

When an atom or its ion has an equal number of electrons when compaired to another element, the two species are isoelectronic.

Basically, if two atoms/ions/radicals have the same number of electrons they are isoelectronic to each other, unless there are d electrons present.

When ions are formed through the loss of electrons, the atom that is to become the ion losses electrons from its highest energy level(its valence shell) first. So, the configuration for Ga is [Ar]4s²3d¹⁰4p¹, but the configuration for Ga⁺³ is [Ar]3d¹⁰. The electrons are lost from the 4p and the 4s subshells first, then from the 3d.

Examples:

• Sodium is isoelectronic to neon when it loses one electron

When Na⁺=[He]2s²2p⁶ it is isoelectronic to Ne=[He]2s²2p⁶

• Chlorine is isoelectronic to argon when it gains an electron

When Cl^-=[Ne]3s²3p⁶ it is isoelectronic to Ar=[Ne]3s²3p⁶

• Gallium⁺³ is not isoelectronic to Nickel, even though both have 28 electrons

When Ga⁺³ [Ar]3d¹⁰ is not isoelectronic to [Ar]4s²3d⁸

Further Information:

See atom, iso, isoelectricity, electronic, electron and electronic configuration.