Describe the trends in melting point and reactivity as you go down Group 0 (the noble gases) and Group 1 (the alkali metals) of the periodic table, and explain why the reactivity trends in these two groups are different from each other.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Group 0 elements are unreactive gases used in lighting and welding. Group 1 elements are highly reactive metals stored under oil to prevent reaction with air and water.
Model answer (5 marks)
Melting point increases down Group 0 because the atoms become larger and the London dispersion forces between them become stronger.
Group 0 elements are unreactive because they have a full outer shell of electrons and therefore have no tendency to gain or lose electrons.
Reactivity increases down Group 1 because the outermost electron is farther from the nucleus and is shielded by more inner shells, so it is easier to lose.
The trends differ because Group 0 elements already have a full valence shell and never need to change their electron count, whereas Group 1 elements have one valence electron that they readily lose, and the ease of loss increases down the group.
Group 0 elements are unreactive because they have a full outer shell of electrons and therefore have no tendency to gain or lose electrons.
Reactivity increases down Group 1 because the outermost electron is farther from the nucleus and is shielded by more inner shells, so it is easier to lose.
The trends differ because Group 0 elements already have a full valence shell and never need to change their electron count, whereas Group 1 elements have one valence electron that they readily lose, and the ease of loss increases down the group.
Examiner tips
- Use the word ‘melting point’ and ‘reactivity’ explicitly. Mention London dispersion forces for Group 0. Explain shielding and distance for Group 1. Show the contrasting reasons for the different trends.
Common mistakes
- Confusing boiling point with melting point. Saying Group 0 elements are reactive. Forgetting to mention shielding when explaining Group 1 reactivity.
Mark scheme (5 marks)
- Melting point increases going down Group 0 (noble gases)
- Group 0 elements are unreactive / do not react because they have a full outer shell of electrons
- Reactivity increases going down Group 1 (alkali metals)
- Going down Group 1, the outer electron is lost more easily because it is further from the nucleus / there is more shielding from inner electron shells
- The trends are different because Group 0 elements have a full outer shell so never need to gain or lose electrons, whereas Group 1 elements have one electron in their outer shell which they lose to react, and this becomes easier down the group
Key terms in this question
Group 0 · Group 1 · reactivity
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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