Lithium, sodium and potassium are all in Group 1 of the periodic table. Explain why these three elements have similar chemical properties, and why their properties differ from the elements in Period 2 of the periodic table.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Lithium has atomic number 3, sodium has atomic number 11, and potassium has atomic number 19. All three are found in Group 1 of the periodic table.
Model answer (5 marks)
All three elements are in Group 1, so each has one valence electron in its outermost shell. The number of valence electrons determines how an atom reacts, so Li, Na and K all lose that single electron to form +1 ions and react similarly with non‑metals. In contrast, elements in Period 2 have two electron shells but different numbers of valence electrons (e.g. He has 2, Li has 1, Be has 2, B has 3, C has 4, N has 5, O has 6, F has 7, Ne has 8). Because their valence‑electron counts differ, their chemical properties are not the same as the Group 1 elements.
Examiner tips
- Mention the single valence electron for Group 1; link to +1 ion formation
- State that Period 2 elements have two shells but varying valence electrons; explain why this gives different chemistry
- Use the phrase "same number of outer electrons" and "different numbers of outer electrons" as per the mark scheme
- Keep answer concise – 5 marks only
Mark scheme (5 marks)
- Elements in the same group have the same number of outer electrons / electrons in the outermost shell
- It is the number of outer electrons that determines chemical properties / reactivity
- Elements in the same group have similar chemical properties (accept: react in a similar way)
- Elements in the same period have the same number of electron shells
- Elements in Period 2 have different numbers of outer electrons (from lithium, sodium and potassium), so they have different chemical properties
Key terms in this question
group · period · chemical properties
Related
- All Eduqas A-Level Chemistry revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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