What are the group properties in the Periodic Table?

Group properties in the Periodic Table refer to the characteristics shared by elements within the same column, or group. These properties include similar chemical behaviors, trends in reactivity, and common physical properties due to having the same number of valence electrons. For example, Group 1 elements, known as alkali metals, are highly reactive and have one valence electron.

Why do elements in the same group have similar properties?

Elements in the same group of the Periodic Table have similar properties because they have the same number of valence electrons. This similarity in electron configuration leads to comparable chemical behaviors and reactivity patterns. For instance, all halogens in Group 17 have seven valence electrons, making them highly reactive non-metals.

How do the properties of Group 1 elements change down the group?

In Group 1, also known as the alkali metals, properties change predictably as you move down the group. Reactivity increases, melting and boiling points decrease, and the density generally increases. These trends are due to the increasing atomic size and the decreasing ionization energy as you move down the group.

What is the significance of Group 18 elements in the Periodic Table?

Group 18 elements, known as noble gases, are significant because they are chemically inert due to having a full valence shell of electrons. This makes them very stable and unreactive under normal conditions. They are used in applications where non-reactivity is crucial, such as in lighting and as inert environments for chemical reactions.

How do transition metals differ from other groups in the Periodic Table?

Transition metals, found in the central block of the Periodic Table, differ from other groups because they have partially filled d subshells. This gives them unique properties such as variable oxidation states, the ability to form colored compounds, and good conductivity of heat and electricity. Unlike the main group elements, they do not follow a single trend in properties across the group.

Why is "Saying Group I reactivity decreases down the group" a common mistake in Group Properties ?

Why it happens: Students apply the Group VII trend (which does decrease) to Group I. How to avoid it: Group I: reactivity INCREASES down (Li < Na < K < Rb < Cs). The outer electron becomes progressively easier to lose. Source: 0654 Examiner Report 2023

Why is "Describing the colour of iodine solution as purple rather than brown" a common mistake in Group Properties ?

Why it happens: Iodine vapour is purple; the solution is brown. Students see 'purple' associated with iodine in images. How to avoid it: Iodine dissolved in water = brown/orange-brown. Iodine dissolved in cyclohexane (non-polar) = violet/purple. In aqueous KI solution: brown.

Why is "Saying a less reactive halogen can displace a more reactive halide" a common mistake in Group Properties ?

Why it happens: Students reverse the direction of displacement. How to avoid it: Only a more reactive halogen can displace a less reactive halide. Cl₂ displaces Br⁻ and I⁻. Br₂ displaces I⁻ only. I₂ cannot displace Cl⁻ or Br⁻.

The Periodic TableCambridge IGCSE Coordinated Sciences 0654

Group Properties

Q: Why is "Describing the colour of iodine solution as purple rather than brown" a common mistake in Group Properties ?

Why it happens: Iodine vapour is purple; the solution is brown. Students see 'purple' associated with iodine in images. How to avoid it: Iodine dissolved in water = brown/orange-brown. Iodine dissolved in cyclohexane (non-polar) = violet/purple. In aqueous KI solution: brown.

Q: Why is "Saying a less reactive halogen can displace a more reactive halide" a common mistake in Group Properties ?

Why it happens: Students reverse the direction of displacement. How to avoid it: Only a more reactive halogen can displace a less reactive halide. Cl₂ displaces Br⁻ and I⁻. Br₂ displaces I⁻ only. I₂ cannot displace Cl⁻ or Br⁻.

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Group I, II, and VII Properties — Cambridge IGCSE Coordinated Science 0654

Group I alkali metals react vigorously with water and are stored in oil. Group VII halogens are reactive non-metals that exist as diatomic molecules and can displace less reactive halogens. Cambridge tests reactions and trends for both groups.

What you’ll learn

Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).

C9.5 — Describe properties and reactions of Group I metals.
C9.6 — Describe properties and reactions of Group VII halogens.
C9.7 — Explain halogen displacement reactions.

Group I — The Alkali Metals

Alkali metals react vigorously with water, becoming more reactive down the group. They are stored in oil to prevent reaction with air/moisture.

Group I elements: Li, Na, K, Rb, Cs, Fr

Physical properties:

Soft, shiny metals (can be cut with a knife)
Low density (Li, Na, K float on water — density < 1 g/cm³)
Low melting point (increases up group) — much lower than typical metals
Good conductors of electricity

Reaction with water (increases in vigour down the group):

2M + 2H₂O → 2MOH + H₂

Li: fizzes gently; Na: faster fizzing; K: violent, flame (H₂ ignites); Rb, Cs: explosive
Product = metal hydroxide (strong alkali) + hydrogen gas

Reaction with oxygen:

4Na + O₂ → 2Na₂O (sodium oxide — white solid) Stored under oil to prevent oxidation

Reaction with chlorine:

2Na + Cl₂ → 2NaCl (sodium chloride — white solid)

Why reactivity increases down group: Outer electron is in a higher energy shell, further from the nucleus, more shielded by inner electrons → easier to lose → more reactive.

Group I: soft, low density, low MP. Stored in oil.
2M + 2H₂O → 2MOH + H₂. Reactivity: Li < Na < K (increases down).
More reactive down: outer electron easier to lose (further from nucleus, more shielded).

Group VII — The Halogens

Halogens are reactive non-metals that exist as diatomic molecules. Reactivity decreases down the group as it becomes harder to gain an electron.

Group VII elements: F₂, Cl₂, Br₂, I₂, At₂

Physical properties:

Halogen	State at r.t.p.	Colour
F₂	Gas	Pale yellow
Cl₂	Gas	Yellow-green
Br₂	Liquid	Orange-brown
I₂	Solid	Dark grey/purple vapour

Reactions with metals:

2Na + Cl₂ → 2NaCl (vigorous, white solid forms) Fe + Br₂ → FeBr₃

Reactions with hydrogen:

H₂ + Cl₂ → 2HCl (reversible, explosive in light) H₂ + F₂ → 2HF (very vigorous — F₂ most reactive) Reactivity: F₂ most vigorous → Cl₂ → Br₂ → I₂ (very slow, reversible)

Halogen displacement reactions: A more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide.

Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq) (orange-brown colour appears) Cl₂(aq) + 2KI(aq) → 2KCl(aq) + I₂(aq) (brown colour appears) Br₂(aq) + 2KI(aq) → 2KBr(aq) + I₂(aq) (brown colour appears) Br₂(aq) + 2KCl(aq) → NO REACTION (Br less reactive than Cl)

Why reactivity decreases down group: The outer shell is further from the nucleus → greater shielding → harder to attract an additional electron → less reactive.

Group VII: diatomic molecules. F₂ (gas, pale yellow) → I₂ (solid, dark grey).
Reactivity: F > Cl > Br > I (decreases down). Harder to gain electron further from nucleus.
Halogen displacement: more reactive halogen displaces less reactive from halide solution.

How it’s examined

Paper 4: 'Write the equation for potassium reacting with water' (2 marks — balanced, state symbols). 'Explain why bromine reacts with potassium iodide solution but not potassium chloride solution' (3 marks — Br more reactive than I but less reactive than Cl; bromine displaces iodide but cannot displace chloride). Halogen displacement questions with observation (colour change) are very common.

Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (C9); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.

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Step-by-step worked examples — Group Properties

Step-by-step solutions to past-paper-style questions on group properties , written exactly the way a tutor would explain them at the board.

1Reaction of potassium with water
Core
Question
Write the balanced equation for the reaction of potassium with water and describe the observations.
Step-by-step solution
1. Step 1
  Potassium reacts vigorously with water to form potassium hydroxide and hydrogen gas.
  $2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$
2. Step 2
  Observations: potassium floats on water (low density); moves rapidly/fizzes across the surface; lilac/violet flame (hydrogen ignites due to heat of reaction); solution becomes alkaline (KOH dissolves).
Answer
$2\text{K} + 2\text{H}_2\text{O} \rightarrow 2\text{KOH} + \text{H}_2$ ; potassium floats, moves rapidly, lilac flame observed.
Examiner tip
The flame colour of potassium is lilac/violet — not yellow (Na) or brick red (Ca).
2Why potassium is more reactive than sodium with water
Extended
Question
Explain why potassium reacts more vigorously with water than sodium.
Step-by-step solution
1. Step 1
  Potassium has one more electron shell than sodium; its outer electron is in the 4th shell compared to sodium's 3rd shell.
2. Step 2
  The outer electron in K is further from the nucleus and more shielded by inner electrons.
3. Step 3
  The nuclear attraction on the outer electron is weaker in K than Na → the outer electron is more easily lost.
4. Step 4
  More readily lost electron → more vigorous reaction with water.
Answer
K has outer electron further from nucleus and more shielded → weaker nuclear attraction → more easily lost → more reactive.
3Halogen displacement — chlorine and potassium iodide
Extended
Question
Chlorine water is added to potassium iodide solution. Describe the observation and explain what is happening, including an equation.
Step-by-step solution
1. Step 1
  The colourless KI solution turns brown/orange-brown.
2. Step 2
  Chlorine is more reactive than iodine; Cl₂ displaces I⁻ from the solution.
  $\text{Cl}_2(\text{aq}) + 2\text{KI}(\text{aq}) \rightarrow 2\text{KCl}(\text{aq}) + \text{I}_2(\text{aq})$
3. Step 3
  Iodine (I₂) is formed; it dissolves in the solution giving a brown/orange-brown colour (turns blue-black with starch).
Answer
Solution turns brown; Cl₂ (more reactive) displaces I⁻: $\text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2$ ; I₂ formed → brown colour.
Examiner tip
To confirm I₂ formation, add starch solution — it turns blue-black. This is an additional confirmatory test.
4Why chlorine is a gas but iodine is a solid at room temperature
Extended
Question
Explain why chlorine is a gas at room temperature but iodine is a solid, given that both are non-polar diatomic molecules.
Step-by-step solution
1. Step 1
  Both Cl₂ and I₂ are simple molecular substances with only van der Waals (London dispersion) forces between molecules.
2. Step 2
  I₂ has larger molecules with more electrons than Cl₂. Larger molecules have stronger van der Waals forces between them.
3. Step 3
  More energy is needed to overcome the stronger van der Waals forces in I₂; its boiling point is higher than room temperature (184 °C vs −34 °C for Cl₂).
4. Step 4
  Cl₂: boiling point below room temperature → gas. I₂: boiling point above room temperature → solid.
Answer
I₂ has larger molecules, stronger van der Waals forces, higher boiling point (solid at room temperature). Cl₂ has smaller molecules, weaker forces, lower boiling point (gas).

Key Definitions and Keywords — Group Properties

Definitions to memorise and the exact keywords mark schemes credit for group properties answers — sharpened from recent examiner reports for the 2026 0654 sitting.

Alkali metals (Group I)
Examiner keyword
The reactive metals lithium, sodium, potassium, rubidium and caesium; each has one outer electron; reactivity increases down the group; all react with water to form a metal hydroxide and hydrogen.
Halogens (Group VII)
Examiner keyword
Non-metal elements fluorine, chlorine, bromine and iodine; each has seven outer electrons; exist as diatomic molecules; reactivity decreases down the group; react with metals to form ionic halide salts.
Halogen displacement reaction
Examiner keyword
A more reactive halogen displaces a less reactive halide ion from its salt solution: e.g. Cl₂ + 2KBr → 2KCl + Br₂. Confirms the reactivity trend.
Diatomic molecule
A molecule consisting of exactly two atoms; halogens exist as diatomic molecules (F₂, Cl₂, Br₂, I₂) as do H₂, N₂, O₂.
Metal halide
An ionic compound formed between a metal and a halogen (e.g. NaCl, KBr, MgI₂); formed when a halogen reacts with a metal.

Common Mistakes and Misconceptions — Group Properties

The traps other students keep falling into on group properties questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.

✕Saying Group I reactivity decreases down the group
0654 Examiner Report 2023
Why it happens
Students apply the Group VII trend (which does decrease) to Group I.
How to avoid it
Group I: reactivity INCREASES down (Li < Na < K < Rb < Cs). The outer electron becomes progressively easier to lose.
✕Describing the colour of iodine solution as purple rather than brown
Why it happens
Iodine vapour is purple; the solution is brown. Students see 'purple' associated with iodine in images.
How to avoid it
Iodine dissolved in water = brown/orange-brown. Iodine dissolved in cyclohexane (non-polar) = violet/purple. In aqueous KI solution: brown.
✕Saying a less reactive halogen can displace a more reactive halide
Why it happens
Students reverse the direction of displacement.
How to avoid it
Only a more reactive halogen can displace a less reactive halide. Cl₂ displaces Br⁻ and I⁻. Br₂ displaces I⁻ only. I₂ cannot displace Cl⁻ or Br⁻.

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