Page 1 — Group 2 overview and electronic structure
What are Group 2 elements?
Group 2 elements (alkaline earth metals) include Be, Mg, Ca, Sr, Ba.
They are metals, and in reactions they tend to lose two electrons to form M²⁺ ions.
Why do they form 2+ ions?
Group 2 atoms have an outer electron configuration of ns².
Example:
● Mg: 1s² 2s² 2p⁶ 3s²
● Ca: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²
They form ions by losing the two outer electrons:
Mg→Mg2++2e−\text{Mg} \rightarrow \text{Mg}^{2+} + 2e^-Mg→Mg2++2e−
Reasoning OCR wants:
● Losing the two outer electrons gives a stable noble gas configuration.
● Forming M²⁺ is energetically and chemically favourable compared with trying to form
M⁺ (which is still reactive and not the common stable ion).
Trends down Group 2: atomic radius
Trend: atomic radius increases down the group.
Reasoning chain:
● Each element down the group has an extra electron shell.
● Outer electrons are in a higher energy level further from the nucleus.
● Increased shells increase shielding, so outer electrons feel less effective nuclear
attraction.
● Therefore the atom is larger.
Trend down Group 2: first ionisation energy
