1. First Ionization energy: %

2. The energy required to remove one electron from the electron donor is its ionization energy (I).

3. The energy gained when an electron is taken up by an Acceptor atom from the valence band of the crystal is the ionization energy of the atom

4. Chemical bonding - Chemical bonding - Covalent bonds: When none of the elements in a compound is a metal, no atoms in the compound have an ionization energy low enough for electron loss to be likely