Why does first ionisation energy decrease down Group 2?

Atomic radius and shielding increase, which outweigh the increased nuclear charge, so the outer electron is held less strongly.

What is the structure of Group 2 metals?

A giant metallic lattice of M²⁺ ions in a sea of delocalised electrons.

How does melting point change down Group 2, in general?

It decreases, though not perfectly smoothly.

Explain the decrease in melting point down Group 2.

The ions get larger, so the attraction to the delocalised electrons is weaker and less energy is needed.

Write the equation for calcium with cold water.

Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

What is formed when magnesium burns in steam?

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

Why are the solutions from Ca, Sr and Ba with water alkaline?

They contain OH⁻ ions from the metal hydroxide.

Write the equation for the extraction of titanium using magnesium.

TiCl₄ + 2Mg → Ti + 2MgCl₂

What is oxidised and what is reduced in the extraction of titanium?

Magnesium is oxidised (0 to +2); titanium is reduced (+4 to 0).

Why is argon used in titanium extraction?

It is unreactive, so it stops titanium and magnesium reacting with oxygen or nitrogen in air.

Trends in Group 2 properties and reactionsAQA A-Level Chemistry: Flashcards

Card 1 of 130 of 13 known

Question

How does atomic radius change down Group 2?

Tap or press Space to reveal

Tap card or press Space to flip

See all 13 cards

How does atomic radius change down Group 2?: It increases, because there are more electron shells.
Why does first ionisation energy decrease down Group 2?: Atomic radius and shielding increase, which outweigh the increased nuclear charge, so the outer electron is held less strongly.
Write the equation for the first ionisation of calcium.: Ca(g) → Ca⁺(g) + e⁻
What is the structure of Group 2 metals?: A giant metallic lattice of M²⁺ ions in a sea of delocalised electrons.
How does melting point change down Group 2, in general?: It decreases, though not perfectly smoothly.
Explain the decrease in melting point down Group 2.: The ions get larger, so the attraction to the delocalised electrons is weaker and less energy is needed.
How does reactivity with water change down Group 2?: It increases.
Write the equation for calcium with cold water.: Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)
What is formed when magnesium burns in steam?: Magnesium oxide and hydrogen: Mg(s) + H₂O(g) → MgO(s) + H₂(g).
Why are the solutions from Ca, Sr and Ba with water alkaline?: They contain OH⁻ ions from the metal hydroxide.
Write the equation for the extraction of titanium using magnesium.: TiCl₄ + 2Mg → Ti + 2MgCl₂
What is oxidised and what is reduced in the extraction of titanium?: Magnesium is oxidised (0 to +2); titanium is reduced (+4 to 0).
Why is argon used in titanium extraction?: It is unreactive, so it stops titanium and magnesium reacting with oxygen or nitrogen in air.

Exam questions on Trends in Group 2 properties and reactions

The first ionisation energies of four Group 2 elements (in kJ mol⁻¹) are: Mg 738, Ca 590, Sr 550, Ba 503.
Explain why the atomic radius of barium is greater than the atomic radius of calcium.2 marks
The melting points of four Group 2 metals are: Mg 923 K, Ca 1115 K, Sr 1050 K, Ba 1000 K.
Explain why barium has a lower melting point than calcium.2 marks
A teacher compares the reactions of Group 2 metals with water. Calcium reacts steadily with cold water. Magnesium shows only a few bubbles with cold water but burns brightly in steam.
Write an equation, including state symbols, for the reaction of calcium with cold water. State and explain whether the resulting solution is acidic or alkaline.3 marks

See the full worksheet

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).