BRAINCAKEGroup 2 and 3
Although there is a general trend in first ionisation energies across a period, and the ionisation energy increases across the period, except from group 2 to group 3.
Boron has a lower ionisation energy than beryllium because outer electron of beryllium is in the 2s sub-shell whilst the outer electron of Boron is in the 2p sub-shell.
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Key terms in this lesson
- Sub-shell
- A subdivision of a main energy level (s, p, d or f) containing orbitals of similar energy.
- 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.
- Group
- A vertical column of the periodic table, containing elements with the same number of outer-shell electrons.
- Period
- A horizontal row of the periodic table, containing elements with the same number of electron shells.
More in Periodicity
- Reactivity
- Hydrogen and Helium
- Periodicity and Period 3 Elements
- Trends in Melting and Boiling Points
- Atomic Radii
- First Ionisation Energy
- Group 5 and 6
- Successive Ionisation Energies
All 14 lessons in Periodicity · All AQA AS-level Chemistry topics