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*Revision Materials and Past Papers* 2.1.1 Atomic structure and isotopes 2.1.2 Compounds, formulae and equations 2.1.3 Amount of substance 2.1.4 Acids 2.1.5 Redox 2.2.1 Electron structure 2.2.2 Bonding and structure 3.1.1 Periodicity 3.1.2 Group 2 3.1.3 The halogens 3.1.4 Qualitative analysis 3.2.1 Enthalpy 3.2.2 Reaction Rates 3.2.3 Chemical equilibrium 4.1 Basic concepts and hydrocarbons 4.1.2 Alkanes 4.1.3 Alkenes 4.2.1 Alcohols 4.2.2 Haloalkanes 4.2.3 Organic synthesis 4.2.4 Analytical techniques 5.1.1 How fast? 5.1.2 How far? 5.1.3 Acids, bases and buffers 5.2.1 Lattice enthalpy 5.2.2 Enthalpy and entropy 5.2.3 Redox and electrode potentials 5.3.1 Transition elements 5.3.2 Qualitative analysis 6.1.1 Aromatic compounds 6.1.2 Carbonyl compounds 6.1.3 Carboxylic acids and esters 6.2.1 Amines 6.2.2 Amino acids, amides and chirality 6.2.3 Polyesters and polyamides 6.2.4 Carbon–carbon bond formation 6.2.5 Organic synthesis 6.3.1 Chromatography and qualitative analysis 6.3.2 Spectroscopy Required Practicals

3.1.2 Group 2

Group 2

Group 2

Specification Reference 3.1.2 (a)–(e)

Quick Notes

  • Group 2 elements have a valence configuration of s2.
  • They form 2+ ions by losing two outer electrons.
  • Act as reducing agents in redox reactions.
  • Reactivity increases from Mg → Ba:
    • With oxygen: Forms white ionic oxides (MO).
    • With water: Forms hydroxides (M(OH)2) + H2 gas.
    • With dilute acids: Forms salts + H2 gas (e.g. Mg + 2HCl → MgCl2 + H2).
  • Reactivity increases down the group due to:
    • Decreasing first and second ionisation energies.
    • More shielding and larger atomic radius = easier to lose electrons.
  • Group 2 oxides react with water to form hydroxides:
    • MO + H2O → M(OH)2
    • Alkalinity of solutions increases down the group.
    • pH values rise (e.g. Mg(OH)2 ~ pH 9; Ba(OH)2 ~ pH 13).
  • Uses of Group 2 bases:
    • Ca(OH)2: Neutralises acidic soil in agriculture.
    • Mg(OH)2 and CaCO3: Used as antacids to relieve indigestion.

Full Notes

Electron Configuration and Ion Formation

Group 2 elements (Be → Ba) have two electrons in their outermost s-orbital. They readily lose these two electrons in chemical reactions to form ions with a 2+.

These are redox reactions, where Group 2 metals are oxidised (lose electrons), and act as reducing agents.

Example Magnesium ion formation

Mg → Mg2+ + 2e−

Reactivity with Oxygen, Water, and Dilute Acids

Group 2 metals become more reactive as you move down the group. You need to know the reactions of Group 2 metals with oxygen, water and dilute acids.

With oxygen (O2):

Group 2 metals react with oxygen (O2), forming solid white oxides:

OCR (A) A-Level Chemistry diagram showing reaction of Group 2 metals with oxygen to form white ionic oxides.

The white solids formed are ionic and have high melting points.

With water:

Group 2 metals (apart from Be) react with water (H2O) forming hydroxides and hydrogen gas:

OCR (A) A-Level Chemistry diagram showing reaction of Group 2 metals with water forming hydroxides and hydrogen gas.

Reaction rate increases from Mg to Ba.

Note that magnesium (Mg) reacts slowly with cold water but more rapidly with steam, forming magnesium oxide, MgO instead.

With dilute acids:

Group 2 metals react with dilute acids forming a salt and hydrogen gas:

OCR (A) A-Level Chemistry reaction of Group 2 metals with dilute acids forming salts and hydrogen gas.

Example Reaction with hydrochloric acid

Mg + 2HCl → MgCl2 + H2

Note: With H2SO4, BaSO4 forms and coats the metal, slowing the reaction due to insolubility of BaSO4.

OCR (A) A-Level Chemistry reaction diagram showing insoluble BaSO4 forming on barium surface during reaction with sulfuric acid.

Zn and Fe (from the d-block) show similar behaviour. These reactions provide experimental evidence of the increasing reactivity down Group 2.

Trend in Reactivity and Ionisation Energies

Reactivity increases down the group because ionisation energies decrease.

OCR (A) A-Level Chemistry graph showing decreasing first ionisation energy down Group 2.

These factors make it easier for outer electrons to be removed.

As two electrons must be lost to form the M2+ ion, both first and second ionisation energies are important in determining reactivity.

Example Second ionisation energy for Magnesium (Mg)

Mg+(g) → Mg2+(g) + e−

Reaction of Group 2 Oxides with Water

Group 2 metal oxides (MO) react with water to form alkaline hydroxide solutions:

OCR (A) A-Level Chemistry diagram showing reaction of Group 2 metal oxides with water forming hydroxides.

MO + H2O → M(OH)2

Alkalinity increases down the group and the solution has a higher pH because the hydroxides become more soluble down the group.

OCR (A) A-Level Chemistry graph showing increasing solubility of Group 2 hydroxides down the group.

This means more OH− ions are released in solution, increasing pH.

Note this is the opposite trend of the Group 2 metal sulfates, their solubilities decrease down the group, with BaSO4 being insoluble.

Uses of Group 2 Compounds as Bases

Group 2 hydroxides and carbonates are basic and are widely used to neutralise acids.

Summary