BRAINCAKEHydrogen and Helium
Different tables place hydrogen in different places on the periodic table. Hydrogen is sometimes placed in group 1 because it has one electron in its outer shell and forms +1 ions like he group 1 metals. It is also sometimes placed above the halogens because it can form -1 ions.
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Key terms in this lesson
- Group
- A vertical column of the periodic table, containing elements with the same number of outer-shell electrons.
More in Periodicity
- s, p, d and f Block
- Groups
- Periods
- Reactivity
- Periodicity and Period 3 Elements
- Trends in Melting and Boiling Points
- Atomic Radii
- First Ionisation Energy
All 14 lessons in Periodicity · All AQA AS-level Chemistry topics