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 the group 1 metals. It is also sometimes placed above the halogens because it can form -1 ions.Helium has two electrons in its outer shell so is 1s2. It is placed in group 0 with the noble gases because it has similar properties, but it is not a p-block element.
Hydrogen and Helium
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Specification: AQA Chemistry (7404), AS-level, 3.2.1.1 Classification. Topic: Periodicity.
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