Ionisation energy

Ionisation is all about removing electrons from atoms to make positive ions.

The first ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions:

M(g)>M+(g)+e-

The second ionisation energy refers to the removal of the next mole of electrons from the mole of gaseous 1+ ions:

M+(g)>M2+(g)+e-

The third ionisation energy refers to M2+(g)>M3+(g)+e-, and so on.

Factors influencing the first ionisation energy

• Nuclear charge - a large nuclear charge means the outer electron is difficult to remove, so the ionisation energy is large.
• Atomic radius - in larger atoms, the outer electron is farther awayfrom and less strongly attracted by the nucleus, so it is easier to remove and the ionisation energy is lower.
• Electron shielding - if more inner electron shells shield the nuclear charge from the outer electron, it will be easier to remove, and the ionisation energy is low.

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