Who this is for: Cambridge IGCSE Coordinated Science (0654) students who want periodic trends — how properties change across periods and down groups — to become reliable marks instead of memorised arrows on a diagram.
What query it owns: how to understand and revise periodic trends in Cambridge IGCSE Coordinated Science.
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.

The periodic table is not just a list of elements — it is a map of how properties change in predictable patterns. Cambridge IGCSE Coordinated Science (0654) expects you to explain trends in atomic size, metallic character, reactivity and melting points across periods and down groups, linking each trend to electron shells and nuclear charge. This guide covers the syllabus patterns, comparison tables examiners expect, and the question types that appear every year.

Key takeaways

• Atomic size decreases across a period (left to right) as nuclear charge increases and electrons are pulled closer.
• Atomic size increases down a group as extra electron shells are added.
• Metallic character decreases across a period; non-metallic character increases.
• Group 1 metals become more reactive down the group; Group 7 halogens become less reactive down the group.
• Trends follow from number of shells, nuclear charge and distance of outer electrons from the nucleus.

What are periodic trends in Cambridge IGCSE Coordinated Science?

Periodic trends are the regular changes in element properties as you move across a period or down a group. Position in the table tells you about electron arrangement, which in turn explains reactivity, bonding and physical properties. Understanding why a trend occurs — not just the direction — is what earns full marks in explain questions.

You can read the full explanation, diagrams and notes on Tutopiya’s Periodic Trends subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Across a period	Same number of shells; nuclear charge increases	”Explain why atomic size decreases across Period 3.”
Down a group	Extra electron shell each time	”Explain why reactivity increases down Group 1.”
Metallic character	Tendency to lose electrons and form positive ions	”State the trend in metallic character across Period 2.”
Reactivity (Group 1)	Easier to lose one outer electron down the group	”Compare reactivity of lithium and potassium.”
Reactivity (Group 7)	Harder to gain one electron down the group	”Explain why fluorine is more reactive than iodine.”

Major trends across a period (left to right)

Property	Trend across Period 3	Reason
Atomic size	Decreases	Nuclear charge increases; same number of shells
Metallic character	Decreases	Harder to lose outer electrons
Non-metallic character	Increases	Easier to gain/share electrons
Melting point (general)	Peaks at Group 4 (Si), then falls	Giant structures vs simple molecules
Type of oxide	Basic → amphoteric → acidic	Change from metal to non-metal

Major trends down a group

Property	Trend down Group 1	Trend down Group 7
Atomic size	Increases	Increases
Reactivity	Increases	Decreases
Melting/boiling point	Decreases	Increases
Density	Generally increases	Increases

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

Command word / phrase	What the question wants	Typical periodic trends stem
Explain	Cause linked to electron structure	”Explain why atomic radius increases down Group 1.”
Describe the trend	State direction without full reason	”Describe the trend in reactivity down Group 7.”
Compare	Differences between two elements	”Compare the reactivity of sodium and rubidium.”
Predict	Apply a trend to an unfamiliar element	”Predict whether element X is more or less reactive than Y.”
State	Short factual answer	”State the trend in metallic character across a period.”

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

1. “Explain why atomic size decreases across a period.” Nuclear charge increases while electrons are added to the same shell, so outer electrons are pulled closer to the nucleus. Mark-scheme reward: increased nuclear charge + same number of shells + electrons pulled closer.
2. “Explain why reactivity increases down Group 1.” Each element has one more electron shell; the outer electron is further from the nucleus and more shielded, so it is lost more easily. Reward: extra shell + further from nucleus + easier to lose electron.
3. “Explain why fluorine is more reactive than bromine.” Fluorine’s outer shell is closer to the nucleus with less shielding, so it gains an electron more easily than bromine. Reward: smaller atomic size + less shielding + gains electron more easily.

Test yourself with the Periodic Trends quiz once you can explain trends without a periodic table in front of you.

How periodic trends connect to the rest of Coordinated Science chemistry

Periodic trends build on atomic structure and lead into Group Properties, Transition Elements and the Reactivity Series. The Cambridge IGCSE Coordinated Science resource hub links every Chemistry subtopic.

Common mistakes students make

• Stating trends without explaining the electron-shell reason.
• Conflicting Group 1 and Group 7 reactivity trends (Group 1 increases down; Group 7 decreases down).
• Saying atomic size increases across a period (it decreases).
• Forgetting shielding when explaining reactivity down a group.
• Mixing up metallic character with reactivity — related but not identical.

When you need more support

If periodic-trends explain questions keep costing marks, work through the Periodic Trends quiz, then get focused help from a Cambridge IGCSE Coordinated Science tutor.

Frequently asked questions

Is periodic trends hard in Coordinated Science? The patterns are straightforward once you link each trend to electron shells and nuclear charge — the explain wording is what separates full marks.

Why does reactivity increase down Group 1 but decrease down Group 7? Group 1 metals lose electrons (easier down the group); Group 7 halogens gain electrons (harder down the group as atomic size increases).

What is metallic character? The tendency of an element to lose electrons and behave as a metal — decreases across a period and generally decreases down non-metal groups.

How do I revise periodic trends effectively? Learn the direction of each trend, practise explain answers using shells and nuclear charge, then take the Periodic Trends quiz.

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