Why does first ionisation energy decrease down a group?

Atomic radius and shielding increase, so the attraction between the nucleus and the outer electron is weaker, despite the increased nuclear charge.

State the trend in reactivity down Group 2.

Reactivity increases (Mg to Ba), because the outer electrons are lost more easily.

What is seen when potassium is added to water?

It melts into a ball, moves rapidly, fizzes and burns with a lilac flame; an alkaline solution forms.

Write the equation for calcium with water.

Ca + 2H₂O → Ca(OH)₂ + H₂

How does magnesium react with water?

Extremely slowly with cold water; it burns in steam to form MgO and H₂.

Give the equation for magnesium burning in oxygen.

2Mg + O₂ → 2MgO (bright white flame, white solid).

State the trend in solubility of the Group 2 hydroxides.

Solubility increases down the group.

State the trend in solubility of the Group 2 sulfates.

Solubility decreases down the group; BaSO₄ is insoluble.

Give the ionic equation for the test for barium ions with sulfate.

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s), a white precipitate.

Why is barium sulfate safe in a barium meal?

It is insoluble, so no toxic Ba²⁺ ions dissolve or are absorbed.

Group 1 and 2 trends and reactionsEdexcel International A Level Chemistry: Flashcards

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Define first ionisation energy.

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Define first ionisation energy.: The energy needed to remove one electron from each atom in one mole of gaseous atoms: X(g) → X⁺(g) + e⁻.
State the trend in first ionisation energy down Group 1 and Group 2.: It decreases down both groups.
Why does first ionisation energy decrease down a group?: Atomic radius and shielding increase, so the attraction between the nucleus and the outer electron is weaker, despite the increased nuclear charge.
State the trend in reactivity down Group 2.: Reactivity increases (Mg to Ba), because the outer electrons are lost more easily.
Write the equation for sodium with water.: 2Na + 2H₂O → 2NaOH + H₂
What is seen when potassium is added to water?: It melts into a ball, moves rapidly, fizzes and burns with a lilac flame; an alkaline solution forms.
Write the equation for calcium with water.: Ca + 2H₂O → Ca(OH)₂ + H₂
How does magnesium react with water?: Extremely slowly with cold water; it burns in steam to form MgO and H₂.
Give the equation for magnesium burning in oxygen.: 2Mg + O₂ → 2MgO (bright white flame, white solid).
Write the equation for sodium oxide with water.: Na₂O + H₂O → 2NaOH
Write the ionic equation for any hydroxide with dilute acid.: OH⁻ + H⁺ → H₂O
State the trend in solubility of the Group 2 hydroxides.: Solubility increases down the group.
State the trend in solubility of the Group 2 sulfates.: Solubility decreases down the group; BaSO₄ is insoluble.
Give the ionic equation for the test for barium ions with sulfate.: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s), a white precipitate.
Why is barium sulfate safe in a barium meal?: It is insoluble, so no toxic Ba²⁺ ions dissolve or are absorbed.

Exam questions on Group 1 and 2 trends and reactions

The first ionisation energies of the Group 2 elements, in kJ mol⁻¹, are: beryllium 900, magnesium 738, calcium 590 and strontium 550. A student is using the data to study how ionisation energy changes down the group.
Explain why the first ionisation energy decreases down Group 2.2 marks
A hospital pharmacy stocks milk of magnesia (a suspension of magnesium hydroxide) as an antacid, and barium sulfate suspension for X-ray examinations of the gut. Soluble barium compounds are toxic.
Explain why barium sulfate is safe to swallow for an X-ray examination, even though soluble barium compounds are toxic.2 marks
A fish farm manager finds that a pond has become acidic, with a hydrogen ion concentration of 1.0 × 10⁻³ mol dm⁻³ (pH 3.0). The pond holds 500 dm³ of water. She plans to add solid calcium oxide to neutralise the acid.
Explain, with an ionic equation, why adding calcium oxide to the pond raises its pH.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).