等电子体是指具有相同价电子数并且具有相同结构的微粒，可以是原子，分子或离子。

具有相同的通式——AX_m，而且价电子总数相等的分子或离子具有相同的结构特征，这个原理称为等电子体原理。

Two or more molecular entities (atoms, molecules, or ions) are described as being isoelectronic with each other if they have the same number of electrons or a similar electron configuration and the same structure (number and connectivity of atoms), regardless of the nature of the elements involved.