First ionisation energy
What First ionisation energy means in Chemistry A-Level, as defined for AQA, OCR.
Definitions of First ionisation energy
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Reference: AQA
The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
The energy needed to remove one mole of electrons from one mole of gaseous atoms, forming one mole of gaseous 1⁺ ions.
The energy needed to remove 1 mol of electrons from 1 mol of gaseous atoms, forming 1 mol of gaseous 1⁺ ions.
Generally rises across a period, with dips at Al and S in Period 3 caused by subshell and pairing effects.
Topics that use First ionisation energy
- Electron configuration (AQA A-Level)
- Fundamental particles (AQA A-Level)
- Group 2, the alkaline earth metals (AQA A-Level)
- Properties of Period 3 elements and their oxides (A-level only) (AQA A-Level)
- Lattice enthalpy (OCR A-Level)
- Periodicity (OCR A-Level)
Related terms
- electrostatic attraction
- hydroxide solubility
- Successive ionisation energies
- 4s before 3d
- alkalinity of the product
- Applying the sequence to specific elements
- atomic radius
- barium sulfate precipitate
Using First ionisation energy in the exam
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