# Explain why the elements in Period 3 show a gradual transition from metallic to non-metallic character across the period, from sodium (Na) to chlorine (Cl).

> IB DP Chemistry Standard Level (2023 syllabus) — S3.1 The periodic table: classification of elements · Explain · 4 marks

## Mark scheme (4 marks)

1. Nuclear charge (number of protons) increases across Period 3, so the nucleus attracts electrons more strongly.
2. Shielding (from inner electrons) remains approximately constant across the period, so effective nuclear charge experienced by valence electrons increases.
3. Elements on the left (e.g. Na, Mg, Al) have few valence electrons and low ionisation energies, so they readily lose electrons — characteristic of metals.
4. Elements on the right (e.g. P, S, Cl) have many valence electrons and high electron affinities / ionisation energies, so they tend to gain or share electrons — characteristic of non-metals.

## Key terms

- [metallic character](https://www.gradenine.co.uk/glossary/metallic-character)
- [non-metallic character](https://www.gradenine.co.uk/glossary/non-metallic-character)

## 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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-elements-in-period-a3c61523) · Published by Druglandscape Ltd.