- The successive ionisation energies of an element increase
- This is because once you have removed the outer electron from an atom, you have formed a positive ion
- Removing an electron from a positive ion is more difficult than from a neutral atom
- As more electrons are removed, the attractive forces increase due to decreasing shielding and an increase in the proton to electron ratio
- The increase in ionisation energy, however, is not constant and is dependent on the atom's electronic configuration
- Taking calcium as an example:
Table Showing the Successive Ionisation Energies of Calcium Table
Electronic Configuration |
1s2 2s2 2p6 3s2 3p6 4s1 |
1s2 2s2 2p6 3s2 3p6 |
1s2 2s2 2p6 3s2 3p5 |
1s2 2s2 2p6 3s2 3p4 |
IE |
First |
Second |
Third |
Fourth |
IE (kJ mol-1) |
590 |
1150 |
4940 |
6480 |
Successive ionisation energies of an element
The ionisation energy increases as you remove more electrons from an element
- The first electron removed has a low IE1 as it is easily removed from the atom due to the spin-pair repulsion of the electrons in the 4s orbital
- The second electron is more difficult to remove than the first electron as there is no spin-pair repulsion
- The third electron is much more difficult to remove than the second one corresponding to the fact that the third electron is in a principal quantum shell which is closer to the nucleus (3p)
- Removal of the fourth electron is more difficult as the orbital is no longer full, and there is less spin-pair repulsion