The Group 2 metals
Introduced| English | Meaning |
|---|---|
| alkaline earth metal/ˈælkəlaɪn ɜːθ ˈmetl/ | alkaline earth metal |
| reactivity/rɪəkˈtɪvɪti/ | The tendency or readiness of a substance to undergo chemical reactions. |
| hydroxide/haɪˈdrɒksaɪd/ | A compound containing hydroxide ions, each consisting of oxygen and hydrogen with a single negative charge. |
| carbonate/ˈkɑːbəneɪt/ | A salt containing the carbonate ion, CO3 with a two-minus charge. |
The alkaline earth metals 碱土金属
- Group 2 holds magnesium, calcium, strontium and barium.
- They all have two outer electrons, lost to form 2+ ions.
- They get more reactive down the group.
Group 2 reactivity ladder
Move down Group 2 and see why reactions become more vigorous.
Group 2 metals form ions with a 2+ charge.
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They lose their two outer electrons.
Why reactivity 反应活性 rises
- Going down, the atoms get larger and hold their two outer electrons less tightly.
- So the electrons are lost more easily → reactivity increases down the group.
Magnesium, a Group 2 metal, burns with a brilliant white flame
Reactivity increases down Group 2 because:
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Larger atoms hold their two outer electrons less tightly, so they are lost more readily.
Reactions of the elements
- with oxygen: burn to an oxide — $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$.
- with water: form a hydroxide 氢氧化物 + hydrogen (faster down the group) — $\text{Ca} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2$. (Mg is slow with cold water, fast with steam.)
- with acid: form a salt + hydrogen — $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$.
Limestone cliffs are calcium carbonate 碳酸盐, a Group 2 compound
A Group 2 metal reacting with water forms:
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e.g. Ca + 2H₂O → Ca(OH)₂ + H₂; the reaction gets faster down the group.
Match each Group 2 fact to the right item.
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Each item links the term to its correct meaning.
Reactions of the compounds
- oxides and hydroxides are basic — they react with water and with acids.
- carbonates react with acids to give a salt, water and carbon dioxide:
$$\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$$
Group 2 reactivity increases down the group as atoms get larger
The oxides and hydroxides of Group 2 metals are:
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They are basic — they react with water and neutralise acids.
A Group 2 carbonate reacting with a dilute acid produces:
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e.g. CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.
You've got it
- Group 2 metals lose two electrons → 2+ ions; reactivity increases down (larger atoms)
- react with oxygen (oxide), water (hydroxide + H₂), acid (salt + H₂)
- oxides/hydroxides are basic; carbonates + acid → salt + water + CO₂