# Lithium (Li), beryllium (Be) and boron (B) are three elements found at the start of Period 2 in the periodic table. Oxygen (O) and sulfur (S) are both in Group 6. Explain how the periodic table is organised and describe the trends in properties you would expect when moving across Period 2 from left to right, and when moving down Group 6 from oxygen to sulfur.

> OCR A-Level Chemistry A (H432) — 3.1 The periodic table and periodicity · Explain · 5 marks

> The periodic table arranges all known elements in order of increasing atomic number. Elements in the same group share similar chemical properties.

## Mark scheme (5 marks)

1. Elements are arranged in order of increasing atomic number (proton number)
2. Elements in the same group have the same number of outer shell electrons / the same number of electrons in their outer shell
3. Across Period 2 from left to right, the number of outer shell electrons increases (from 1 in lithium to a full outer shell in neon)
4. Going down Group 6 from oxygen to sulfur, the number of electron shells increases
5. Going down Group 6, the elements show similar chemical properties because they have the same number of outer shell electrons / oxygen and sulfur both have 6 outer electrons

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](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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Source: [GradeNine](https://www.gradenine.co.uk/q/lithium-li-beryllium-be-and-boron-ff0b1403) · Published by Druglandscape Ltd.