Group 1: the alkali metals Cambridge IGCSE Chemistry (9–1) revision
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In plain words
Lithium, sodium and potassium are metals, but odd ones: soft enough to cut with a knife, light enough to float, and so reactive they have to be kept under oil. Drop one in water and it fizzes about, making hydrogen and leaving an alkali behind. That is why they are called the alkali metals.
Three things to know
- The Group 1 (I) metals are soft with low densities and low melting points. Going down the group they get more reactive, and their melting points get lower.
- With water they give a metal hydroxide (an alkali) and hydrogen: 2Na + 2H₂O → 2NaOH + H₂. Lithium fizzes steadily, sodium melts into a ball and skates about, potassium catches fire with a lilac flame.
- Each atom has one outer electron, which it loses to form a 1+ ion. Further down the group that electron is further from the nucleus and is lost more easily.
Tips and tricks
- The trend: reactivity increases down Group 1. Use it to predict rubidium and caesium: even more violent.
- Product of metal + water is the hydroxide, not the oxide: sodium hydroxide and hydrogen.
It lands in your notebook with its questions as flashcards.
Group 1: the alkali metals: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
How does reactivity change going down Group 1?
The outer electron is lost more easily further down.
Which gas is made when an alkali metal reacts with water?
Metal + water → metal hydroxide + hydrogen.
What kind of solution is left when sodium reacts with water?
Sodium hydroxide is an alkali.
Why are the alkali metals stored under oil?
They react quickly with both.
How many electrons are in the outer shell of a Group 1 atom?
The group number is the number of outer electrons.
What colour flame is seen when potassium reacts with water?
The hydrogen catches fire and the potassium colours the flame.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 7 marks. Write your answers on paper, then check them.
Group 1: the alkali metals
Cambridge IGCSE Chemistry (9–1) 0971 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Give two things you would see when a small piece of sodium is added to water.[2]
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Any two: it floats; it fizzes; it melts into a ball; it moves around on the surface; it gets smaller and disappears.
Write a word equation and a balanced symbol equation for the reaction of potassium with water.[2]
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Potassium + water → potassium hydroxide + hydrogen. 2K + 2H₂O → 2KOH + H₂.
Explain why potassium is more reactive than lithium.[2]
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Its outer electron is further from the nucleus (there are more shells), so it is less strongly attracted and is lost more easily.
Predict how the reaction of rubidium with water compares with that of potassium.[1]
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More violent (it would explode).
Answers: Group 1: the alkali metals
- 1. Any two: it floats; it fizzes; it melts into a ball; it moves around on the surface; it gets smaller and disappears.
- 2. Potassium + water → potassium hydroxide + hydrogen. 2K + 2H₂O → 2KOH + H₂.
- 3. Its outer electron is further from the nucleus (there are more shells), so it is less strongly attracted and is lost more easily.
- 4. More violent (it would explode).