Group 1Edexcel GCSE Chemistry: Revision notes
Section 1
What is Group 1, and what are alkali metals like physically?
Group 1 elements — lithium, sodium, potassium, rubidium, caesium and francium — are known as the alkali metals. Their position (leftmost column) determines their chemistry.
Alkali metals are:
- Soft — soft enough to cut with a knife
- Low melting point relative to typical metals, and melting point decreases going down the group
Section 2
How do lithium, sodium and potassium react with water?
Lithium, sodium and potassium all react with water to produce a metal hydroxide (an alkali) and hydrogen gas:
alkali metal + water → metal hydroxide + hydrogen
e.g. 2Na + 2H2O → 2NaOH + H2
Observations:
- All three float, move around the surface, and fizz as hydrogen is released
- Lithium: fizzes steadily, floats and moves around
- Sodium: fizzes more vigorously, melts into a ball due to heat released
- Potassium: reacts violently, melts, and the hydrogen produced ignites, burning with a lilac flame
Word equation for the reaction: potassium + water → potassium hydroxide + hydrogen.
Section 3
What is the pattern in reactivity down Group 1?
Reactivity increases going down Group 1: lithium < sodium < potassium. This pattern lets you predict that rubidium and caesium (further down) would react even more violently with water than potassium.
Examiners often ask you to 'predict' the reaction of rubidium — state that it would react more violently/vigorously than potassium, since reactivity increases down the group.
Section 4
Why does reactivity increase down Group 1?
This trend is explained by electronic configuration. Each Group 1 atom has one electron in its outer shell, which is lost to form a 1+ ion when the metal reacts.
Going down the group:
- Atoms have more electron shells, so the outer electron is further from the nucleus
- The outer electron is more shielded from the attraction of the positive nucleus by the extra inner shells
- This makes the outer electron easier to lose
Because the outer electron is lost more easily, reactivity increases down the group.
Do not just say 'more shells means more reactive' without explaining why: the key reasoning is that the outer electron is further from the nucleus and more shielded, so it is easier to lose.
Must Know
- Group 1 elements are the alkali metals: soft, low melting point
- Lithium, sodium and potassium all react with water to form a metal hydroxide + hydrogen gas
- Potassium reacts most violently of the three (hydrogen ignites, lilac flame); lithium reacts least violently
- Reactivity increases down Group 1
- This is because atoms have more shells, so the single outer electron is further from the nucleus and more shielded, making it easier to lose
- Group 1 atoms all have one electron in their outer shell, forming 1+ ions
That's the notes covered.
Carry on to the next subtopic.