Who this is for: Cambridge IGCSE Chemistry (0620) students who want periodic trends — how properties change across a period and down a group — to become predictable patterns instead of isolated facts.
What query it owns: how to understand and revise periodic trends in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the periodic trends revision-guide angle, while Tutopiya’s Periodic Trends subtopic page owns the learning resource and the free Periodic Trends quiz owns the practice.

Periodic trends describe how element properties change systematically across the Periodic Table. In Cambridge IGCSE Chemistry (0620), examiners test metallic character, reactivity of Groups I and VII, and simple comparisons of atomic size and proton number. Understanding why a trend occurs — linked to outer electrons and nuclear charge — earns explanation marks. This guide covers the trends that appear every series, how to answer “explain” questions, and where to practise.

Key takeaways

• Metallic character decreases across a period (left to right) as elements become more non-metallic.
• Group I metals become more reactive down the group — outer electron is further from the nucleus.
• Group VII halogens become less reactive down the group — harder to gain an electron.
• Atomic size generally increases down a group and decreases across a period (same shell, more protons).
• Always explain trends using electronic structure and distance from nucleus, not just “it increases”.

What are periodic trends in Cambridge IGCSE Chemistry?

Periodic trends are the predictable changes in physical and chemical properties as you move across a period or down a group. Cambridge IGCSE Chemistry focuses on metallic vs non-metallic character, reactivity patterns in Groups I and VII, and simple atomic-size reasoning. Each trend has an underlying cause in electron shells and nuclear attraction.

Read the full notes on Tutopiya’s Periodic Trends subtopic page before attempting questions.

The core trends you must master

Trend	Direction	Underlying reason
Metallic character	Decreases across Period 3	Easier to lose electrons on the left; non-metals gain electrons on the right
Group I reactivity	Increases down the group	Outer electron further from nucleus → easier to lose
Group VII reactivity	Decreases down the group	Harder to attract an extra electron as atom is larger
Atomic size	Increases down a group	Extra electron shell
Atomic size	Decreases across a period	Same shell; more protons pull electrons closer

How to answer periodic trend questions — step by step

1. Identify whether the question is about a period or a group.
2. State the trend clearly (increases / decreases).
3. Give the electronic reason — outer electron distance, shielding, or nuclear charge.
4. Name the elements in the question to make the answer specific.
5. Check command word — “describe” needs less detail than “explain”.

Test yourself with the free Periodic Trends quiz once you have worked through a few examples.

Across a period vs down a group: which trend applies?

Question focus	Trend to use	Typical signal words
Period 3 oxides	Change from basic → amphoteric → acidic	”across Period 3”, “sodium to chlorine”
Group I reactivity	Increases down	”lithium to caesium”, “alkali metals”
Group VII reactivity	Decreases down	”fluorine to iodine”, “halogens”
Metal vs non-metal	Metallic character decreases across	”metallic character”, “Period 2”

Periodic trends in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical trend stem
Describe	State the trend without full reason	”Describe the trend in reactivity down Group I.”
Explain	Trend + electronic structure reason	”Explain why chlorine is more reactive than iodine.”
Compare	Two named elements	”Compare the reactivity of sodium and potassium.”
Predict	Apply a known trend	”Predict which is more reactive: fluorine or bromine.”

Worked exam-style stems (how to answer the wording)

1. “Describe the trend in metallic character across Period 3.” Metallic character decreases from sodium (metal) to chlorine (non-metal). Reward: named endpoints.
2. “Explain why potassium is more reactive than sodium.” Outer electron is further from the nucleus and more shielded → easier to lose. Reward: distance/shielding, not just “bigger atom”.
3. “Explain why fluorine is more reactive than chlorine.” Fluorine’s outer shell is closer to the nucleus → stronger attraction for an incoming electron. Reward: nuclear attraction linked to size.

When you can recognise the wording instantly, work through the Periodic Trends quiz and Group Properties to lock the patterns in.

How periodic trends connect to the rest of the course

Trends build on The Periodic Table layout and feed into Group Properties and the Reactivity Series. The Cambridge IGCSE Chemistry resource hub links all units.

Common mistakes students make

• Applying a group trend to a period question (or vice versa).
• Saying Group VII reactivity increases down the group — it decreases.
• Explaining trends without mentioning electrons or nuclear charge.
• Confusing atomic size with relative atomic mass.
• Stating “more shells” for trends across a period — shell number stays the same.

When you need more support

If “explain” trend questions keep losing marks, work through the Periodic Trends quiz to find the gap, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What is the most tested periodic trend in IGCSE Chemistry? Group I and Group VII reactivity trends appear frequently, along with metallic character across Period 3.

Does atomic size increase or decrease across a period? It decreases — electrons are in the same shell but nuclear charge increases, pulling electrons closer.

Why do halogens get less reactive down the group? The outer shell is further from the nucleus, so it is harder to attract an extra electron.

How do I revise periodic trends effectively? Learn one trend at a time with its electronic reason, then take the Periodic Trends quiz before mixing group and period questions.

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