# Potassium iodide is an ionic compound formed when potassium reacts with iodine. Explain how potassium iodide is formed from its elements, and why the compound has a high melting point.

> Edexcel A-Level Chemistry (9CH0) — 2.1 Ionic bonding · Explain · 5 marks

> Potassium (K) is in Group 1 of the periodic table. Iodine (I) is in Group 7 of the periodic table. Potassium iodide (KI) is used in table salt and some medical treatments.

## Mark scheme (5 marks)

1. Potassium loses one electron (from its outer shell) to form a K⁺ ion
2. Iodine gains one electron (into its outer shell) to form an I⁻ ion
3. Both ions achieve a full outer shell / stable electronic configuration (like a noble gas)
4. There are strong electrostatic forces of attraction between the oppositely charged K⁺ and I⁻ ions (ionic bonds)
5. A large amount of energy is needed to break the many strong electrostatic forces of attraction / ionic bonds throughout the giant ionic lattice, so the melting point is high

## Key terms

- [ion](https://www.gradenine.co.uk/glossary/ion)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/potassium-iodide-is-an-ionic-compound-1b473c65) · Published by Druglandscape Ltd.