1 OUTER ELECTRON — they lose this electron easily to form +1 ions.
SOFT — can be cut with a knife.
LOW DENSITY — lithium, sodium and potassium all float on water.
LOW MELTING AND BOILING POINTS compared to other metals.
Shiny when freshly cut — but quickly tarnish in air (react with oxygen).
Stored under OIL to prevent reaction with air and water.
React vigorously with WATER to produce hydrogen gas and metal hydroxide (an alkali — hence 'alkali metals').
Reactions with Water
All Group 1 metals react with water to produce a METAL HYDROXIDE and HYDROGEN GAS:
General equation:
Metal + water → metal hydroxide + hydrogen
2M + 2H₂O → 2MOH + H₂
Specific reactions:
2Li + 2H₂O → 2LiOH + H₂
(Lithium: fizzes gently, moves around on the surface)
2Na + 2H₂O → 2NaOH + H₂
(Sodium: fizzes vigorously, moves rapidly, may catch fire)
2K + 2H₂O → 2KOH + H₂
(Potassium: reacts very vigorously, the hydrogen gas ignites immediately with a lilac flame)
The resulting solution is ALKALINE — the metal hydroxide (LiOH, NaOH, KOH) is a strong alkali. Adding universal indicator to the solution turns it PURPLE.
As you go DOWN the group, reactions become MORE vigorous — potassium is more reactive than sodium, which is more reactive than lithium.
Why Reactivity Increases Down Group 1
Reactivity INCREASES going DOWN Group 1 — this is explained by atomic structure.
Going down the group:
ATOMS GET LARGER — more electron shells are added.
OUTER ELECTRON is in a higher shell — further from the nucleus.
Electrostatic attraction from nucleus to outer electron DECREASES (greater distance AND more shielding from inner electrons).
Outer electron is MORE EASILY LOST.
More reactive → more easily loses the outer electron.
Memory aid: further = weaker pull = easier to lose = more reactive.
This is why rubidium and caesium (further down) are so reactive they must be handled with extreme care — they can ignite explosively in water or air.
⚠️ Common Mistake
Reactivity INCREASES down Group 1 (opposite to Group 7). This is because the outer electron gets further from the nucleus and is more easily lost. Going down Group 1: more shells → outer electron further away → weaker attraction → MORE reactive. Going down Group 7: non-metals get LESS reactive (harder to attract an extra electron).
📐 Key Equations
2M + 2H₂O → 2MOH + H₂
2Li + 2H₂O → 2LiOH + H₂
2Na + 2H₂O → 2NaOH + H₂
2K + 2H₂O → 2KOH + H₂
📌 Key Note
Group 1: alkali metals, 1 outer electron, form +1 ions. Soft, low density, low melting point. React with water → metal hydroxide + hydrogen. Reactivity INCREASES down group (outer electron further from nucleus, less attracted, more easily lost).
🎯 Matching Activity — Match the Group 1 Reaction
Match each alkali metal to its reaction description with water. — drag the symbols on the right to match the component names on the left.
Lithium
Drop here
Sodium
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Potassium
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All Group 1 metals
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Reactivity trend
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Increases down Group 1 — outer electron is further from nucleus, less strongly attracted
Reacts very vigorously, hydrogen ignites immediately with a lilac/purple flame
Fizzes vigorously, moves rapidly, may ignite — more reactive than lithium
React with water to produce a metal hydroxide (alkali) and hydrogen gas
Fizzes gently, moves around on water surface — less vigorous than others
⭐ Higher Tier Only
Quantitative explanation: increasing atomic radius down group → outer electron in higher shell → greater distance from nucleus → weaker electrostatic attraction → lower ionisation energy → more easily lost → more reactive. Predict properties of Rb and Cs.
🎯 Test Yourself
Question 1 of 2
1. What are the products when sodium reacts with water?
2. Why is potassium more reactive than lithium?
⭐ How Well Do You Understand This Topic?
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