OxfordAQA International GCSE Chemistry: Group properties (9202) – Revision Notes

These revision notes condense section 3.7.1 Group properties of the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. They cover statements a to f. The qualification is untiered, so every point here is for every candidate, and no required practical is attached to this section. For full teaching and longer worked examples, use the group properties study guide.

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The one-line summary

Group 1 metals lose one electron and get more reactive going down. Group 7 non-metals gain one electron and get less reactive going down. Both trends come from the outer electrons sitting in a higher energy level further down a group.

Group 1, the alkali metals (3.7.1 a and b)

Property	What to remember
Outer electrons	One
Density	Low for metals; Li, Na and K are less dense than water and float
Ion formed	M⁺ (charge +1)
Compounds with non-metals	Ionic; white solids; dissolve to give colourless solutions
With water	Release hydrogen; form the metal hydroxide
Hydroxide solution	Alkaline (pH above 7), because it contains OH⁻ ions
Trend down the group	More reactive

Equations to be able to write

2M + 2H₂O → 2MOH + H₂          any Group 1 metal with water
2M + X₂  → 2MX                 with a halogen (X = Cl, Br, I)
4M + O₂  → 2M₂O                with oxygen

Water reaction, side by side

Lithium	Sodium	Potassium
Floats, steady fizzing	Floats, melts into a ball, moves about quickly	Floats, hydrogen ignites with a lilac flame

Further down means faster and more violent, but the same products.

Test for the gas: a lighted splint placed near hydrogen gives a pop.

Method in steps: formula of a Group 1 compound

1. Write the ions: M⁺ and the non-metal ion (Cl⁻, Br⁻, O²⁻, S²⁻ …).
2. Balance charges to zero: one M⁺ per 1− ion, two per 2− ion.
3. Write the formula: RbCl, Na₂O, K₂S.
4. In an equation, write the non-metal element as a molecule where it is diatomic (Cl₂, O₂).

Worked reminder. 2.3 g of sodium burns in chlorine. Moles of Na = 2.3 ÷ 23 = 0.10 mol. 2Na + Cl₂ → 2NaCl, so 0.10 mol NaCl. Mr NaCl = 58.5, so mass = 5.85 g.

Group 7, the halogens (3.7.1 c and d)

Property	What to remember
Outer electrons	Seven
Form of the element	Diatomic molecules: F₂, Cl₂, Br₂, I₂
With metals	Ionic compounds containing halide ions with charge 1−
Ion names	fluoride, chloride, bromide, iodide
Reactivity down the group	Decreases
Melting and boiling points down the group	Increase

States at room temperature

Fluorine	Chlorine	Bromine	Iodine
pale yellow gas	pale yellow-green gas	red-brown liquid	grey-black solid

Gas to liquid to solid matches rising boiling points. Bigger molecules lower in the group have stronger forces between molecules.

Metal halide formulae. Balance the metal ion’s charge with enough 1− halide ions:

Mg²⁺ + Br⁻ → MgBr₂        Al³⁺ + I⁻ → AlI₃        Li⁺ + F⁻ → LiF

Equation pattern for a 2+ metal: Mg + Cl₂ → MgCl₂.

Displacement (3.7.1 e)

A halogen higher in Group 7 pushes a lower one out of a dissolved salt of that lower halogen.

Reactivity:  Cl₂ > Br₂ > I₂   (fluorine above all, but it reacts with water)

Mix	Result	Colour change
Chlorine + bromide solution	Bromine formed	colourless to yellow-orange
Chlorine + iodide solution	Iodine formed	colourless to brown
Bromine + iodide solution	Iodine formed	turns brown
Bromine + chloride solution	No reaction	stays the colour of the added bromine water
Iodine + chloride or bromide	No reaction	stays the colour of the added iodine solution

Method in steps: writing a displacement equation

1. Compare positions: the halogen being added must sit above the halide already in the salt; otherwise the answer is “no reaction”.
2. Exchange partners: the added halogen ends up as halide ions in the new salt, and the original halide is released as the element.
3. Keep the salt’s formula balanced (a 2+ metal needs two halide ions).
4. Ionic version: leave out the metal ion. Example: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂.

Worked reminder. Chlorine water + lithium bromide solution: Cl₂ + 2LiBr → 2LiCl + Br₂. The solution turns yellow-orange.

Explaining reactivity (3.7.1 f)

Specification idea: the higher the energy level of the outer electrons, the more easily electrons are lost and the less easily they are gained. You may answer in terms of energy levels or shells.

Chain for Group 1 (use every link): more energy levels → outer electron further from nucleus → more shielding → weaker attraction → electron lost more easily → more reactive.

Chain for Group 7 (use every link): more energy levels → outer level further from nucleus → more shielding → weaker attraction for an incoming electron → electron gained less easily → less reactive.

Predicting an unfamiliar element

Questions often name an element you have not studied in detail, such as francium or astatine. Use the group pattern, not memory.

If the element is …	Predict
Lower in Group 1 than potassium	Same products with water (hydroxide + hydrogen), faster and more violent reaction, 1+ ion, white compounds
Lower in Group 7 than iodine	Higher melting and boiling points than iodine, so a solid; less reactive than iodine; forms a 1− ion
A halogen above another	It displaces the lower one from its salt solution

Always give the reason: “because it is further down the group” earns more than the prediction alone.

Calculations that appear with this unit

Mole questions often borrow these reactions. Keep three habits:

1. Write the balanced equation first and read the mole ratio from it.
2. Use the diatomic Mr for a halogen element (Cl₂ = 71, Br₂ = 160).
3. Gas volume at room temperature and pressure = moles × 24 dm³ (or × 24 000 cm³).

Worked reminder. 0.30 mol of lithium is added to water. Equation: 2Li + 2H₂O → 2LiOH + H₂, so 0.15 mol of hydrogen, which is 0.15 × 24 000 = 3600 cm³. The 0.30 mol of LiOH left in solution makes it alkaline.

Must-know distinctions

Easily confused	The difference
Chlorine vs chloride	Cl₂ molecules make up the element chlorine; Cl⁻ ions in a compound are called chloride
Lose vs gain	Group 1 atoms lose one electron; Group 7 atoms gain one
Reacts vs dissolves	Sodium reacts with water; sodium hydroxide dissolves in it
More reactive down vs less reactive down	Group 1 up the scale, Group 7 down the scale
Hydrogen vs hydroxide	Hydrogen is the gas given off; hydroxide is the OH⁻ in the solution

Quick self-test

1. State the charge on the ion formed by any alkali metal.
2. Name the gas released when caesium reacts with water.
3. Write the formula of rubidium sulfide.
4. Which three alkali metals float on water?
5. A Group 1 hydroxide solution is tested with universal indicator. Give the colour and a possible pH.
6. Write the formula of aluminium iodide.
7. Does bromine water react with potassium chloride solution? Give a reason.
8. Give the ionic equation when chlorine meets iodide ions.
9. Astatine is below iodine. Predict its state at room temperature.
10. What volume of hydrogen, measured at RTP, forms when 0.10 mol of potassium reacts with water? (Molar gas volume 24 dm³)
11. Give two reasons why fluorine is more reactive than chlorine, using the energy-level idea.
12. Describe the appearance of a solution of a Group 1 chloride.

Answers

1. +1 (1+).
2. Hydrogen.
3. Rb₂S.
4. Lithium, sodium and potassium.
5. Blue or purple; any pH above 7, for example 13.
6. AlI₃.
7. No. Chlorine is higher in the group and more reactive, so bromine cannot replace it.
8. Cl₂ + 2I⁻ → 2Cl⁻ + I₂.
9. Solid (melting point rises down Group 7).
10. 2K + 2H₂O → 2KOH + H₂, so 0.050 mol H₂. Volume = 0.050 × 24 = 1.2 dm³.
11. Fluorine’s outer level is closer to the nucleus (lower energy level) and less shielded, so the attraction for an extra electron is stronger and it gains an electron more easily.
12. Colourless.

Where marks are usually lost

• Writing halogens as single atoms (Cl instead of Cl₂) and then failing to balance the equation.
• Stating that alkali metals dissolve in water rather than react with it.
• Naming oxygen instead of hydrogen as the gas from Group 1 and water.
• Giving the Group 7 reactivity explanation in terms of losing electrons.
• Stopping the explanation at “the atom is bigger” without distance, shielding and weaker attraction.
• Saying a less reactive halogen displaces a more reactive one, or writing an equation for a reaction that does not happen.
• Describing displacement colour changes vaguely (“it changes colour”) when the question asks what is seen.
• Mixing up the trends: melting and boiling points rise down Group 7, while reactivity falls.
• Giving a coloured solution for a Group 1 compound.

For full explanations go back to the study guide; for exam-style practice use the practice questions. The transition metals notes compare those metals with Group 1, the electrolysis notes reuse halide ions at the anode, and the diagnostics will show where else to focus.

Official syllabus

OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, published by OxfordAQA. These notes cover section 3.7.1 Group properties (statements a to f).