Why does first ionisation energy decrease down Group 2?

Atomic radius and shielding increase, so the outer electrons are less strongly attracted to the nucleus.

How does reactivity change down Group 2, and why?

It increases, because the outer electrons are lost more easily.

Write the equation for calcium with water.

Ca + 2H₂O → Ca(OH)₂ + H₂

What does magnesium form with steam?

Magnesium oxide and hydrogen: Mg + H₂O(g) → MgO + H₂

What is the trend in solubility of Group 2 hydroxides?

Solubility increases down the group.

What is the trend in solubility of Group 2 sulfates?

Solubility decreases down the group.

What does CaO form with water?

Calcium hydroxide: CaO + H₂O → Ca(OH)₂ (an alkaline solution).

What is the trend in thermal stability of Group 2 carbonates, and why?

Stability increases down the group as the cation gets larger, with lower charge density and less polarising power.

What products form when Group 2 nitrates are heated?

The oxide, brown nitrogen dioxide and oxygen: 2M(NO₃)₂ → 2MO + 4NO₂ + O₂

What happens when sodium nitrate is heated?

It forms sodium nitrite and oxygen: 2NaNO₃ → 2NaNO₂ + O₂

Why does lithium nitrate decompose differently from sodium nitrate?

Li⁺ is the smallest Group 1 ion with the highest charge density, so it polarises the nitrate more: 4LiNO₃ → 2Li₂O + 4NO₂ + O₂

What are the flame colours of Li, Na, K, Ca and Ba?

Li red, Na yellow, K lilac, Ca brick-red, Ba apple-green.

How do flame colours arise?

Electrons promoted by heat fall back to lower energy levels, emitting visible light of specific wavelengths.

Group 1 and 2 elements and their compoundsEdexcel A-Level Chemistry: Flashcards

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What is the trend in first ionisation energy down Group 2?

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What is the trend in first ionisation energy down Group 2?: It decreases.
Why does first ionisation energy decrease down Group 2?: Atomic radius and shielding increase, so the outer electrons are less strongly attracted to the nucleus.
How does reactivity change down Group 2, and why?: It increases, because the outer electrons are lost more easily.
Write the equation for calcium with water.: Ca + 2H₂O → Ca(OH)₂ + H₂
What does magnesium form with steam?: Magnesium oxide and hydrogen: Mg + H₂O(g) → MgO + H₂
What is the trend in solubility of Group 2 hydroxides?: Solubility increases down the group.
What is the trend in solubility of Group 2 sulfates?: Solubility decreases down the group.
What does CaO form with water?: Calcium hydroxide: CaO + H₂O → Ca(OH)₂ (an alkaline solution).
What is the trend in thermal stability of Group 2 carbonates, and why?: Stability increases down the group as the cation gets larger, with lower charge density and less polarising power.
What products form when Group 2 nitrates are heated?: The oxide, brown nitrogen dioxide and oxygen: 2M(NO₃)₂ → 2MO + 4NO₂ + O₂
What happens when sodium nitrate is heated?: It forms sodium nitrite and oxygen: 2NaNO₃ → 2NaNO₂ + O₂
Why does lithium nitrate decompose differently from sodium nitrate?: Li⁺ is the smallest Group 1 ion with the highest charge density, so it polarises the nitrate more: 4LiNO₃ → 2Li₂O + 4NO₂ + O₂
What are the flame colours of Li, Na, K, Ca and Ba?: Li red, Na yellow, K lilac, Ca brick-red, Ba apple-green.
How do flame colours arise?: Electrons promoted by heat fall back to lower energy levels, emitting visible light of specific wavelengths.

Exam questions on Group 1 and 2 elements and their compounds

The first ionisation energies of three Group 2 elements are: magnesium 738 kJ mol⁻¹, calcium 590 kJ mol⁻¹ and barium 503 kJ mol⁻¹.
Explain the trend in first ionisation energy down Group 2.2 marks
A technician investigates the reactions of Group 2 oxides and hydroxides with water and with dilute acids.
Write the equation for the reaction of magnesium oxide with dilute hydrochloric acid, and the equation for the reaction of calcium hydroxide with dilute nitric acid.2 marks
A student heats samples of Group 1 and Group 2 nitrates and carbonates strongly in a hard glass test tube and records the changes.
Write the equation for the thermal decomposition of magnesium nitrate and state the colour of the gas given off.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).