# Explain why the melting points of the Group 1 metals decrease down the group from lithium to caesium.

> IB DP Chemistry Higher Level (2023 syllabus) — S2.3 The metallic model · Explain · 4 marks

## Mark scheme (4 marks)

1. Metallic bonding involves electrostatic attraction between delocalised electrons and positive metal ions (cations).
2. Going down Group 1, the ionic radius increases, so the distance between the nucleus and the delocalised electrons increases.
3. The larger ions also have more shielding from inner electron shells, reducing the effective nuclear charge experienced by the delocalised electrons.
4. As a result, the metallic bond becomes weaker down the group, so less energy is required to overcome it, and the melting point decreases.

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