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Successive Ionisation Energies

The first ionisation energy is the least endothermic as energy is needed to remove an electron from a neutral atom. In a +1 ion, the proton:electron ratio is increased. The same number of protons are attracting fewer electrons and the effective nuclear charge is increased.

The second ionisation energy is therefore more endothermic than the first as more energy is needed to remove and electron from a +1 ion. The third electron needs even more energy than the second, and so on.A large jump in successive ionisation energies occurs when an electron is being removed from a shell closer to the nucleus. For example,The first five ionisation energies of Magnesium are: 737, 1450, 7731, 10545 and 13627 kJmol^-1.There is a large jump between the second and third ionisation energies. Magnesium has two electrons in the outermost shell. The third electron is being removed from a shell closer to the nucleus.This is evidence that electrons are arranged in shells.
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

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Specification: AQA Chemistry (7404), AS-level, 3.1.1.3 Electron configuration. Topic: Atomic Structure.

Key terms in this lesson

First ionisation energy: The enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.
Second ionisation energy: The energy needed to remove one electron from each ion of one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions, under standard conditions.
Endothermic: Describes a reaction in which energy is transferred from the surroundings to the system, so the enthalpy change is positive.
Period: A horizontal row of the periodic table, containing elements with the same number of electron shells.

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