AQA GCSE Combined Science (8464), Higher tier · Chemistry › Atomic structure and the periodic table › The periodic table
Practise Group 1. 15 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.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Explain the name 'alkali metals'They react with water to form hydroxides that dissolve to give alkaline solutions.
4
Describe their reactions with waterThey float and fizz; sodium melts into a ball; potassium's hydrogen burns with a lilac flame.
4
State the reactivity trend down Group 1Reactivity increases going down the group: lithium, then sodium, then potassium.
5
Write equations for their reactionsWith water, oxygen and chlorine, e.g. 2K + 2H2O → 2KOH + H2.
6
Explain their similar reactions using electronsThey all have one electron in their outer shell, which they lose to form 1+ ions.
6
Predict properties of rubidium and caesiumUse the trends: even more vigorous reactions and similar products, e.g. RbOH and RbCl.
7
Explain why reactivity increases down Group 1The outer electron is further from the nucleus, so it is less strongly attracted and more easily lost.
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
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.
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.
Cheatsheet
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
How to answer each type of question
Give observations for a reaction with water
2 to 3 marks4
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.
Show the model answer
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 marks5
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.
More shells, so the outer electron is further from the nucleus.
Weaker attraction between the nucleus and the outer electron.
So the outer electron is lost more easily.
Example. Explain why potassium is more reactive than sodium. Answer in terms of electrons.
Show the model answer
A potassium atom has more shells, so its outer electron is further from the nucleus (1). There is weaker attraction between the nucleus and the outer electron (1). So potassium loses its outer electron more easily (1).
Predict the properties of another alkali metal
2 to 3 marks6
Use the same type of products as sodium or potassium.
Use the trend: further down means more reactive.
Example. Rubidium is below potassium in Group 1. (a) Give the formula of rubidium chloride. (b) Predict how the reaction of rubidium with water compares with the reaction of potassium with water. (c) Name the alkaline substance formed when rubidium reacts with water.
Show the model answer
(a) RbCl (1) (b) Rubidium reacts more vigorously / faster / more violently (1) (c) rubidium hydroxide (1)
Shortcuts and memory tricks
Down Group 1: more shells → further away → easier to lose → more reactive.
Water equation pattern for every alkali metal (M): 2M + 2H2O → 2MOH + H2.
Saying the sodium dissolves. It reacts, gets smaller and disappears.
Saying the gas made with water is oxygen. It is hydrogen.
Saying the outer electron is harder to lose down the group. It is easier.
Writing only 'the atoms get bigger' without linking it to distance, attraction and losing the electron.
Wrong formulae: Na2O not NaO; H2 not H.
Exam technique
For 'explain the trend', use the three-step chain (distance, attraction, electron lost more easily). Each step is usually a mark.
Observation questions want what you see or hear (fizzing, moving, melting, a flame), not 'hydrogen is made'.
Use comparative words: more vigorously, faster, further from the nucleus, weaker attraction.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Sodium is a Group 1 element. What name is given to the elements in Group 1?
the alkali metals
Potassium burned with a coloured flame. What colour was the flame?
lilac
Lithium burns in oxygen to form lithium oxide, Li2O. Balance the equation. ....Li + O2 → ....Li2O
4Li + O2 → 2Li2O
Write a half equation for the formation of a potassium ion from a potassium atom.
K → K+ + e−
Write a balanced symbol equation for the reaction of M with water. Use M as the symbol for the metal.
2M + 2H2O → 2MOH + H2
Name the gas produced when a Group 1 metal reacts with water.
hydrogen
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Sodium is a Group 1 element.
(a) What name is given to the elements in Group 1?[1]
(b) Group 1 metals are stored under oil. Suggest why.[1]
(c) Complete the word equation for the reaction of sodium with water. sodium + water → .................... + ....................[2]
(d) Universal indicator was added to the solution formed. What is the pH of the solution? Tick (✓) one box.[1]
1
5
7
13
Show the answer and mark scheme
(a)Answer: the alkali metals
alkali metals
(b)Answer: To stop them reacting with oxygen and water vapour in the air.
to stop them reacting with oxygen / water (vapour) / air
(c)Answer: sodium hydroxide + hydrogen
sodium hydroxide
hydrogen
(d)Answer: 13
Question 2Medium6 marks
Group 1 metals react with oxygen and with chlorine.
(a) Lithium burns in oxygen to form lithium oxide, Li2O. Balance the equation. ....Li + O2 → ....Li2O[1]
(b) Write a balanced symbol equation for the reaction of potassium with chlorine.[2]
(c) Describe the appearance of the product of the reaction between potassium and chlorine.[1]
(d) A freshly cut surface of sodium is shiny, but it quickly becomes dull. Explain why.[2]
Show the answer and mark scheme
(a)Answer: 4Li + O2 → 2Li2O
4Li + O2 → 2Li2O
(b)Answer: 2K + Cl2 → 2KCl
correct formulae: K + Cl2 → KCl
balanced: 2K + Cl2 → 2KCl
(c)Answer: white solid
white solid
(d)Answer: Sodium reacts with oxygen in the air, forming a layer of sodium oxide.
sodium reacts with oxygen (in the air)
forming (a layer of) sodium oxide
Question 3Hard6 marks
A teacher demonstrated the reactions of lithium, sodium and potassium with water. Universal indicator had been added to the water in each trough.
Describe what the students would observe in the three reactions. Explain why the reactivity of the metals changes down the group.[6]
Show the answer and mark scheme
Answer: Li fizzes slowly; Na melts, fizzes and darts about; K melts, burns with a lilac flame. Hydrogen and an alkaline hydroxide form. Reactivity increases down the group because the outer electron is further from the nucleus and is lost more easily.
lithium: floats, fizzes steadily and moves slowly (does not melt)
sodium: floats, melts into a ball, fizzes quickly and moves rapidly across the surface
potassium: melts, fizzes violently and burns with a lilac flame / may spark or explode
the metal gets smaller and disappears
the indicator turns (from green to) blue / purple because an alkaline metal hydroxide forms
hydrogen gas is produced, e.g. 2Na + 2H2O → 2NaOH + H2
reactivity increases down the group
the atoms get larger / the outer electron is further from the nucleus
so the attraction between the nucleus and the outer electron is weaker
so the outer electron is lost more easily
Marked with levels of response: the full level descriptors are in the app.