AQA GCSE Chemistry Foundation (8462), Foundation tier · Atomic structure and the periodic table › The periodic table
Practise Group 1. 8 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
The alkali metals in Group 1: their reactions with oxygen, chlorine and water, why they react in similar ways, and why they get more reactive down the group. Expect observations, balanced equations and 'explain the trend' questions, which are very common.
Key facts
Group 1 = alkali metals: one outer electron; form 1+ ions
metal + water → metal hydroxide + hydrogen
2Na + 2H2O → 2NaOH + H2
4Na + O2 → 2Na2O
2Na + Cl2 → 2NaCl
Reactivity increases down the group
Down the group: outer electron further from nucleus → weaker attraction → lost more easily
Soft, low density, low melting point; stored under oil
Notes
The alkali metals
Group 1 contains lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs) and francium (Fr).
They all have one electron in their outer shell, which gives them similar chemical properties.
In reactions each atom loses its outer electron to form an ion with a 1+ charge, e.g. Na+. Their compounds are ionic.
They are soft metals that can be cut with a knife, with low densities: lithium, sodium and potassium float on water. Their melting points are low and decrease down the group.
They react quickly with oxygen and water in the air, so they are stored under oil. A freshly cut surface is shiny but soon tarnishes.
Reactions with water
metal + water → metal hydroxide + hydrogen, e.g. 2Na + 2H2O → 2NaOH + H2
The hydroxide dissolves to form an alkaline solution: universal indicator turns blue or purple.
Lithium floats and fizzes steadily. Sodium fizzes rapidly, melts into a ball and moves around on the surface. Potassium reacts even more vigorously and the hydrogen burns with a lilac flame.
In each case the metal gets smaller and disappears as it reacts.
Reactions with oxygen and chlorine
With oxygen they form metal oxides: 4Li + O2 → 2Li2O; 4Na + O2 → 2Na2O; 4K + O2 → 2K2O.
With chlorine they react vigorously to form metal chlorides, which are white solids: 2Na + Cl2 → 2NaCl.
Each of these reactions is more vigorous going down the group.
Why reactivity increases down the group
diagram
Going down the group the atoms have more shells, so the outer electron is further from the nucleus.
The attraction between the nucleus and the outer electron is weaker.
Down Group 1 the outer electron (red) is further from the nucleus, so it is lost more easily.
So the outer electron is lost more easily, and the metal is more reactive.
Use the trend to predict: rubidium and caesium react with water even more violently than potassium, forming rubidium hydroxide and caesium hydroxide.
How to answer each type of question
Give observations for a reaction with water
2 to 3 marksGrade 4
Give things you would see or hear, not the names of products.
Give as many separate observations as there are marks.
Example. A small piece of sodium is added to a trough of water containing a few drops of universal indicator. Give three observations.
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Any three: fizzing / bubbles (1); the sodium floats (1); it melts into a ball (1); it moves around on the surface (1); it gets smaller and disappears (1); the indicator turns blue / purple (1).
Write a balanced equation
1 to 2 marksGrade 5
Write the correct formulae: hydroxides MOH, oxides M2O, chlorides MCl; hydrogen is H2, oxygen O2, chlorine Cl2.
Balance the equation, then count each element on both sides.
Example. Lithium reacts with water to form lithium hydroxide and hydrogen. Write a balanced symbol equation for this reaction.