# Explain why the standard enthalpy of atomisation of a metal is always a positive value, and describe the role that this step plays in a Born–Haber cycle for an ionic compound.

> IB DP Chemistry Standard Level (2023 syllabus) — R1.2 Energy cycles in reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. Atomisation involves breaking metallic bonds / converting the metal from solid to gaseous atoms, which requires energy input.
2. Because energy is absorbed / the process is endothermic, ΔH atomisation is always positive.
3. In a Born–Haber cycle, atomisation is the step that produces gaseous metal atoms from the standard-state solid metal, which is necessary before ionisation (removal of electrons) can occur.
4. The atomisation enthalpy contributes to the overall (Hess's law) energy cycle, meaning a larger atomisation enthalpy makes the formation of the ionic compound less energetically favourable (less exothermic overall), unless offset by other terms such as lattice enthalpy.

## Key terms

- [standard enthalpy of atomisation](https://www.gradenine.co.uk/glossary/standard-enthalpy-of-atomisation)
- [Born–Haber cycle](https://www.gradenine.co.uk/glossary/born-haber-cycle)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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