Chemistry AS (Electrons, Bonding and Structure)

Revision notes for Chemistry OCR A.


Ionisation Energies.

Ionisation energy is the energy required to create positive ions.

- The first ionisation energy is a measure of how easily an atom loses an electron to form a 1+ ion.

Na > (Na+) + e-

Factors Affecting Ionisation Energy

- Atomic radius = the bigger the atomic radius, the easier it is to pull an electron off because it isn't experiencing a big nuclear attraction from the centre, therefore it has a lower ionisation energy.

- Nuclear charge = the closer it is to the nucleus, the more nuclear attraction it faces and the more attracted it is to the nucleus. This makes it harder to rip the outer electrons off, therefore it needs a higher ionisation energy,

-Electron shielding = larger atoms have more inner shells, so it decreases the amount of nuclear attraction experienced by the outer electrons because inner shells repel the outer shell electrons. Therefore, less nuclear attraction means a lower ionisation energy.

Successive Ionisation Energies

(The energy required to remove each electron in turn. An element has the same number of ionisation energies as it has electrons.)

Each successive ionisation energy is bigger than the one before it because the remaining electrons will experience less repulsion and will be drawn slightly closer to the nucleus. Moreover, as the distance between the nucleus and outer electron gets smaller, nuclear attraction gets larger so it requires more energy to pull the electron off. This means more ionisation energy is needed.

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