# Explain why the melting point of tungsten (W) is significantly higher than that of calcium (Ca), even though both metals are described using the metallic bonding model.

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

> Tungsten has a melting point of 3422 °C and belongs to Period 6, Group 6. Calcium has a melting point of 842 °C and belongs to Period 4, Group 2.

## Mark scheme (4 marks)

1. Both metals consist of a lattice of positive ions (cations) surrounded by a 'sea' of delocalised electrons, and melting requires overcoming electrostatic attraction between the ions and delocalised electrons.
2. Tungsten contributes more delocalised electrons per atom than calcium (up to 6 valence electrons available for delocalisation versus 2 for calcium), resulting in a higher charge density of the electron sea.
3. Tungsten ions carry a higher ionic charge (W can exhibit high oxidation states, effectively contributing a higher nuclear/ionic charge) than Ca²⁺, increasing the electrostatic attraction between the cations and the electron sea.
4. The combined effect of higher ionic charge and greater number of delocalised electrons makes the metallic bonds in tungsten much stronger, requiring significantly more energy to overcome, hence the much higher melting point.

## Key terms

- [metallic bonding](https://www.gradenine.co.uk/glossary/metallic-bonding)
- [melting point](https://www.gradenine.co.uk/glossary/melting-point)

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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