Successive ionisation energies increase because the remaining electrons are pulled closer to the nucleus after each electron is lost and the nuclear attraction on the remaining electrons increases.
Large jumps in ionisation energies provide evidence for electrons existing in shells. A large jump indicates the electron is being removed from a shell closer to the nucleus.
Successive ionisation energies of period 2 elements in kJmol-1
The second ionisation energy is the energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions.
Mg+(g) → Mg2+(g) + e-
Large jumps in ionisation energies provide evidence for electrons existing in shells. A large jump indicates the electron is being removed from a shell closer to the nucleus.
Successive ionisation energies of period 2 elements in kJmol-1
| e- | 1st I.E. | 2nd I.E. | 3rd I.E. | 4th I.E. | 5th I.E. | 6th I.E. | 7th I.E. | 8th I.E. | 9th I.E. | |
| Li | 1 | 520 | 7300 | |||||||
| Be | 2 | 900 | 1760 | 14850 | ||||||
| B | 3 | 800 | 2430 | 3660 | 25020 | |||||
| C | 4 | 1090 | 2350 | 4620 | 6220 | 37830 | ||||
| N | 5 | 1400 | 2860 | 4580 | 7480 | 9440 | 53270 | |||
| O | 6 | 1310 | 3390 | 5300 | 7470 | 10980 | 13330 | 71330 | ||
| F | 7 | 1680 | 3370 | 6050 | 8410 | 11020 | 15160 | 17870 | 92040 | |
| Ne | 8 | 2080 | 3950 | 6120 | 9370 | 12180 | 15240 | 20000 | 23070 | 115380 |