Periodic Table | GCSE Chemistry

Atomic structure

Lesson overview

This lesson introduces the core chemistry idea, the useful equipment and the calculation or data skills used on this page.

Focusperiodic table groups, periods and trends

Time45-60 minutes

EquipmentPeriodic table, calculator and notebook.

Practical linkpattern evidence from Group 1, Group 7 and transition metals

Maths tagsinterpreting tables and predicting trends

What you will learn

Describe the key chemistry ideas behind periodic table patterns.
Use precise GCSE command-word language in explanations.
Apply the idea to unfamiliar substances, data or practical contexts.
Check answers using units, state symbols, observations or balanced equations where relevant.

Core knowledge

The modern periodic table is arranged by atomic number.
Elements in the same group have the same number of outer-shell electrons, so they often have similar chemical properties.
Group 1 metals become more reactive down the group because the outer electron is further from the nucleus and easier to lose.
Group 7 halogens become less reactive down the group because it is harder for a larger atom to gain an electron.
Noble gases are unreactive because they have full outer electron shells.

Periodic table reference for this lesson

Use this mini-table for the practice on this page. Atomic numbers increase from left to right across each period.

Element	Symbol	Atomic number	Group	Period	Useful GCSE note
Lithium	Li	3	1	2	Group 1 metal; one outer electron
Sodium	Na	11	1	3	Group 1 metal; electron arrangement 2,8,1
Potassium	K	19	1	4	More reactive than sodium
Fluorine	F	9	7	2	Most reactive halogen in GCSE comparisons
Chlorine	Cl	17	7	3	Displaces bromide and iodide ions
Bromine	Br	35	7	4	Less reactive than chlorine
Argon	Ar	18	0	3	Noble gas with a full outer shell

Periodic table patterns infographic

Illustrated GCSE Chemistry infographic showing groups, periods, electron shells, Group 1 and Group 7 reactivity trends and ion charges. — Use this infographic to connect groups, periods, outer-shell electrons and reactivity trends in the periodic table.Download visual

Periodic Table practice set

Use the worked examples and practice questions on this page as a complete study task: learn the group and period meanings, summarise the infographic in your own words, then answer the questions using the data, equations and observations given here. Check every answer for interpreting tables and predicting trends.

Clear explanation

Periodic table patterns is built around periodic table groups, periods and trends. Start by learning what group and period mean, then connect them to the sequence in the infographic.

The key GCSE skill is to move from evidence to explanation: name the observation, data trend, particle model, structure or reaction, then explain why it supports the conclusion.

For calculation or data work, show interpreting tables and predicting trends. For written explanations, include the specific chemistry reason rather than a memorised topic sentence.

Worked examples

Core example: sodium

Sodium is in Group 1, so it has one outer-shell electron.

Sodium is in Period 3, so it has three occupied shells.

Fill the shells for the first 20 elements.

Answer: Sodium has electron arrangement 2,8,1.

Extension example: halogen displacement

Chlorine is above bromine in Group 7.

Chlorine is more reactive than bromine.

A more reactive halogen displaces a less reactive halide.

Answer: Cl2 + 2KBr -> 2KCl + Br2.

Quick checks

Choose an answer, then check your thinking.

1. Why do Group 1 elements have similar reactions?

Same mass number Same outer-shell electron count They are all gases

2. What happens to Group 1 reactivity down the group?

Decreases Stays identical Increases

Practice questions

Question 1

State what a group is.

Reveal answer and marking guidance

Answer: A vertical column in the periodic table.

Marking: Credit vertical column.

Question 2

Explain why potassium is more reactive than sodium.

Reveal answer and marking guidance

Answer: Potassium's outer electron is further from the nucleus and more shielded, so it is lost more easily.

Marking: Credit distance, shielding and easier electron loss.

Question 3

Predict whether bromine displaces iodine from potassium iodide.

Reveal answer and marking guidance

Answer: Yes. Bromine is above iodine in Group 7, so it is more reactive.

Marking: Credit correct prediction and reactivity comparison.

Question 4

Give two properties of transition metals.

Reveal answer and marking guidance

Answer: Examples include high density, high melting point, coloured compounds, variable ions and catalytic activity.

Marking: Credit any two valid properties.

Practice ladder

FluencyRecall the key definition, symbol, structure, equation or observation.

ApplicationApply periodic table patterns to unfamiliar substances, practicals or data.

Practical interpretationUse evidence, method quality, uncertainty or conclusion wording where asked to evaluate.

Maths skillUse units, ratios, graphs and significant figures accurately.

Answers and marking guidance

The exact practice answers are hidden under each question so you can try first. Marks come from using the correct chemistry model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as particles, ions, bonds, energy, rate, evidence and uncertainty.

Common mistakes

Using mass number instead of atomic number for table order.
Reversing the Group 1 and Group 7 trends.
Forgetting group number links to outer-shell electrons.
Saying noble gases are reactive because they are gases.

Extension challenge

Create a six-line revision card for periodic table patterns: two definitions, one infographic detail or equation line, one equation or data check, one common mistake, and one complete explanation sentence using group, period, reactivity.

Reveal answer

Example answer: A complete response names the chemistry model, uses accurate units or observations, and explains why the evidence supports the conclusion.