Module 3: Periodic Table and Energy · Year 12
3.1.2 Group 2
Use the ns² outer configuration to explain Group 2 ions, reactions and the increasing reactivity down the group, then apply the hydroxides and carbonates as bases.
What you need to know
Open a line for a quick recap. If it feels obvious, move straight to the linked practice.
3.1.2 a Describe Group 2 outer-shell s2 configuration and loss of these electrons to form 2+ ions. Quick revision
Every Group 2 atom has two electrons in its outer s sub-shell: an outer configuration of ns². In its usual chemistry, the atom loses both of those electrons to form M²⁺.
For calcium, [Ar]4s² becomes Ca²⁺ with the [Ar] configuration. The proton number stays the same; you are only changing the electron count.
3.1.2 b Write and explain Group 2 reactions with oxygen, water and dilute acids. Quick revision
For the common Group 2 reactions, the metal is being oxidised to M²⁺. With oxygen you normally form the oxide, with water you form the hydroxide plus hydrogen, and with a dilute non-oxidising acid you form a salt plus hydrogen.
I’d learn the patterns, then build the balanced equation for the metal you are given. For calcium and water, one Ca atom gives Ca²⁺, so the balanced equation is Ca + 2H₂O → Ca(OH)₂ + H₂.
3.1.2 c Explain increasing Group 2 reactivity down the group using first and second ionisation energies. Quick revision
A Group 2 reaction usually requires the atom to lose two electrons, so think about both the first and second ionisations. Down the group, those outer electrons are further from the nucleus and more shielded, so the attraction to the nucleus is weaker.
First and second ionisation energies therefore decrease overall, making formation of M²⁺ easier. That is why the metals become more reactive as you go down Group 2.
3.1.2 d Describe reactions of Group 2 oxides with water and the trend in alkalinity of the solutions. Quick revision
Group 2 oxides are basic. With water they form hydroxides, so the solution contains OH⁻ ions and is alkaline: MO + H₂O → M(OH)₂.
As you go down the group, the hydroxides become more soluble. That gives a higher concentration of OH⁻ in a saturated solution, so the alkalinity increases. Be careful here: you are explaining the pH trend mainly through hydroxide solubility, not by saying the OH⁻ ion itself becomes “more basic”.
3.1.2 e Explain why selected Group 2 compounds act as bases and write equations for uses such as liming acidic soil and antacid action. Quick revision
When you use these Group 2 compounds as bases, think about the H⁺ they remove. Calcium hydroxide can be used to neutralise acidic soil, while magnesium hydroxide and calcium carbonate are familiar antacid examples.
The equation depends on the base. A hydroxide gives salt + water; a carbonate gives salt + carbon dioxide + water. You can often write the cleanest explanation as an ionic equation with H⁺.