TL;DR

Trend questions carry the most marks in CIE 0620 Topic 8. This guide gives you the 4-step logic chain examiners require, covers all tested groups (I, VII, 0, transition metals), and includes 6 past paper questions with model answers. Jump to "Periodic Trends Explained" if that's your priority.

The periodic table is tested in every CIE 0620 paper. According to Cambridge International Education's published mark schemes, incomplete trend explanations are the most common reason students lose marks, even when they understand the concept.

Working with a specialist IGCSE Chemistry tutor covers every syllabus point in this guide with exam-focused sessions.

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What is the periodic table in IGCSE Chemistry?

The periodic table arranges all known elements by increasing atomic number. Elements with similar properties sit in the same vertical column. CIE provides the full table in every exam paper.

Each element box carries four pieces of information.

What you see	What it means	Example: Sodium
Atomic number	Number of protons in nucleus	11
Symbol	Chemical shorthand	Na
Relative atomic mass	Average mass across isotopes	23
Group position	Outer electron count	Group I

You can derive electron configuration directly from position in the table.

What are groups and periods and how do they differ?

Groups and periods each tell you something different about atomic structure.

Feature	What it is	What it tells you	Example
Group	Vertical column	Number of outer electrons	Group I = 1 outer e⁻
Period	Horizontal row	Number of electron shells	Period 3 = 3 shells
Group number	I, II, III...	Ion charge (main groups)	Group VII = −1 ion
Period number	1 to 7	Atomic size (roughly)	P4 bigger than P3

A staircase line divides metals (left) from non-metals (right). Silicon sits on it as a metalloid.

How do you find electron configuration from position?

Period number = number of shells. Group number = outer electrons. Fill in order: 2, 8, 8. Chlorine (Period 3, Group VII) = 2, 8, 7. Potassium (Period 4, Group I) = 2, 8, 8, 1.

What's the difference between metals and non-metals?

Key properties compared. Silicon is the metalloid exception for IGCSE.

Property	Metals	Non-Metals	Silicon (metalloid)
Conductivity	Good conductor	Poor conductor	Semi-conductor
Melting point	High (mostly)	Low (mostly)	High (giant covalent)
Malleability	Malleable, ductile	Brittle	Brittle
Oxide type	Basic	Acidic	Amphoteric
Ion formed	Cation (+)	Anion (−)	Neither typical

Silicon's oxide (SiO₂) is amphoteric — it reacts with both acids and alkalis.

Periodic trends explained (CIE 0620)

Periodic trends are repeating patterns in element properties as you move through the table. Two directions matter at IGCSE: going down a group and going across a period.

Group I reactivity increases going down. Group VII reactivity decreases. Both explained by the same electron shell logic chain.

What happens going down a group?

TREND CHAIN

More electron shells added going down
Outer electron sits further from the nucleus
More inner shells = greater shielding of outer electrons
Nuclear attraction on outer electrons weakens
Group I: outer e⁻ lost more easily → reactivity INCREASES
Group VII: outer e⁻ gained less easily → reactivity DECREASES

What happens going across a period (left to right)?

Period 3 (Na to Ar) is the standard CIE 0620 case study.

Element	Type	Oxide type	Oxide in water
Na	Metal	Basic	Alkaline solution
Mg	Metal	Basic	Slightly alkaline
Al	Metal	Amphoteric	Neutral / both
Si	Metalloid	Acidic (weak)	Insoluble
P, S, Cl	Non-metal	Acidic	Acidic solution
Ar	Noble gas	None	Does not react

Oxide type shifts from basic (left) to acidic (right) as elements change from metal to non-metal.

What's the 4-step logic chain every examiner wants?

Write each step as a separate sentence. Miss one and you lose a mark.

4-STEP MARK SCHEME CHAIN

Step 1: Going down the group, the number of electron shells increases.

Step 2: The outer electron is further from the nucleus.

Step 3: There is greater shielding from inner electron shells.

Step 4: The electrostatic attraction between the nucleus and outer electron is weaker.

Group I conclusion: Outer electron lost more easily = MORE reactive.

Group VII conclusion: Outer electron gained less easily = LESS reactive.

How do you answer a trend question for full marks?

Trend questions give 3 to 4 marks. Each mark = one step in the logic chain. Write numbered sentences, not a paragraph block.

4-mark model answer: Group I

EXAM-STYLE QUESTION [4 MARKS]

Explain why potassium reacts more vigorously with water than sodium.

MODEL ANSWER

(1 mark) Potassium has more electron shells than sodium.

(1 mark) The outer electron in potassium is further from the nucleus.

(1 mark) Potassium's outer electron is more shielded by inner shells.

(1 mark) The nuclear attraction on the outer electron is weaker, so it's lost more easily.

3-mark model answer: Group VII

EXAM-STYLE QUESTION [3 MARKS]

Explain why iodine is less reactive than chlorine.

MODEL ANSWER

(1 mark) Iodine has more electron shells than chlorine.

(1 mark) The outer shell in iodine is further from the nucleus and more shielded.

(1 mark) The nuclear attraction on an incoming electron is weaker; iodine gains electrons less easily.

EXAM TRAP

Writing "the atom is bigger so it's less reactive" scores zero. The chain must include: more shells → outer shell further away → more shielding → weaker nuclear attraction. Partial chains get partial marks.

What is Group I (alkali metals) and what's tested?

Na has 3 shells (2,8,1). K has 4 shells (2,8,8,1). More shells = outer electron further from nucleus = easier to lose = more reactive.

Group I metals are lithium, sodium, and potassium. All have one outer electron they lose easily. They're stored under oil to prevent reactions with air or water vapour.

MEMORY TRICK

Group I order: Little Naughty Kids Rub Cats' Fur (Li, Na, K, Rb, Cs, Fr)

Down the group: melting point DECREASES · density INCREASES · reactivity INCREASES

Key properties of Group I metals

All six properties come from having one outer electron.

Soft enough to cut with a knife
Lower density than most metals — Li, Na, K float on water
React vigorously with water, oxygen, and halogens
All form +1 ions in compounds
All compounds are white and dissolve to give colourless solutions
Reactivity increases going down the group

How do Group I metals react with water?

General equation: 2M(s) + 2H₂O(l) → 2MOH(aq) + H₂(g)

Metal	Observation	Reactivity
Lithium	Floats, steady fizzing, dissolves	Least reactive of the three
Sodium	Darts on surface, vigorous fizzing	More reactive than Li
Potassium	Ignites, burns with a lilac flame	Most reactive of the three

Vigour increases because the outer electron gets easier to lose going down the group.

EXAM TRAP

"Potassium is more reactive because it has more electrons." → ZERO marks. Required chain: more shells → outer e⁻ further → more shielding → weaker nuclear attraction → e⁻ lost more easily.

What is Group VII (halogens) and what's tested?

Halogens are fluorine, chlorine, bromine, and iodine. All have 7 outer electrons and form −1 ions. All exist as diatomic molecules. Reactivity decreases going down the group.

MEMORY TRICK

Halogen order: Friendly Cats Bring Icy Afternoons (F, Cl, Br, I, At)

Down the group: boiling point INCREASES · density INCREASES · reactivity DECREASES

What do halogens look like at room temperature?

These exact descriptions are tested directly. "Greenish" won't score the mark.

Halogen	State	Exact colour	Formula
Fluorine	Gas	Pale yellow	F₂
Chlorine	Gas	Pale yellow-green	Cl₂
Bromine	Liquid	Red-brown	Br₂
Iodine	Solid	Grey-black / purple vapour	I₂

Fluorine is rarely tested at IGCSE. Focus on Cl, Br, and I.

How do displacement reactions work?

A more reactive halogen displaces a less reactive one from its salt solution.

Reaction	Observation	Occurs?
Cl₂ + KBr(aq)	Turns orange-brown	Yes — Cl more reactive than Br
Cl₂ + KI(aq)	Turns brown-black	Yes — Cl more reactive than I
Br₂ + KI(aq)	Turns brown-black	Yes — Br more reactive than I
Br₂ + KCl(aq)	No colour change	No — Br less reactive than Cl
I₂ + any halide	No colour change	No — I least reactive

Only a more reactive halogen can displace a less reactive one. Never the reverse.

EXAM TRAP

"Bromine displaces chlorine from NaCl solution." → Wrong, scores zero. Bromine is less reactive than chlorine. It cannot displace it.

Why are noble gases (Group 0) unreactive?

Noble gases have a full outer electron shell. Helium has 2. All others have 8. They don't need to gain, lose, or share electrons. They exist as single atoms (monatomic), not molecules.

Each noble gas use is tied to a specific property.

Noble gas	Key use	Property used
Helium	Balloons / airships	Low density, non-flammable
Neon	Advertising signs	Glows red-orange with electricity
Argon	Welding / bulbs	Inert, prevents oxidation
Krypton	Specialist lighting	Inert atmosphere

Boiling points increase going down Group 0 as atoms get larger and intermolecular forces grow.

EXAM TRAP

"Noble gases are stable because they don't react." → Circular, scores zero. Required: they have a full outer electron shell, so they don't need to gain, lose, or share electrons.

What makes transition metals different from Group I?

Transition metals form the central d-block between Groups II and III. Iron, copper, and zinc are the key IGCSE examples. Three specific properties set them apart.

Three special properties to memorise.

Variable oxidation states: Fe forms Fe²⁺ and Fe³⁺; Cu forms Cu⁺ and Cu²⁺
Coloured compounds: FeCl₂ is pale green; CuSO₄ is blue; Fe₂O₃ is orange-brown
Catalytic activity: iron (Haber process), MnO₂ (H₂O₂ decomposition), Pt (car exhausts)

Five contrasts between transition metals and Group I metals.

Property	Transition metals	Group I metals
Melting point	Very high	Low
Density	High	Low (float on water)
Compound colour	Coloured (varies)	White or colourless
Oxidation states	Variable (e.g. Fe²⁺, Fe³⁺)	Fixed +1 only
React with water	Slow or no reaction	Very vigorous
Used as catalysts	Yes	No

Variable oxidation states explain why iron forms both FeCl₂ and FeCl₃ in different conditions.

Who developed the periodic table and why does it matter?

Scientist	What they did	Key contribution
Mendeleev	Ordered by atomic mass (1869)	Left gaps; predicted undiscovered elements
Moseley	Ordered by atomic number (1913)	Fixed anomalies; gave modern periodic law

Mendeleev's gaps are a frequent exam question. He predicted gallium and germanium from patterns in surrounding elements. When discovered, both matched his predictions closely.

Past paper style questions with model answers

These six questions match CIE 0620 command words, mark allocations, and style. Attempt each question before reading the model answer.

Q1 — Group I trend [3 marks]

EXAM-STYLE QUESTION [3 MARKS]

Describe the trend in reactivity of Group I metals going down the group. Explain this trend using atomic structure.

MODEL ANSWER

(1) Reactivity increases going down Group I.

(1) Each lower element has more electron shells; the outer electron is further from the nucleus and more shielded.

(1) The nuclear attraction on the outer electron is weaker, so it's lost more easily.

Q2 — Group VII displacement [3 marks]

EXAM-STYLE QUESTION [3 MARKS]

Aqueous chlorine is added to potassium bromide solution. State what you would observe and explain why the reaction occurs.

MODEL ANSWER

(1) The solution turns orange-brown (bromine forms).

(1) Chlorine displaces bromide ions from the solution.

(1) Chlorine is more reactive than bromine — its outer shell is closer to the nucleus, so it gains electrons more easily.

Q3 — Noble gas stability [2 marks]

EXAM-STYLE QUESTION [2 MARKS]

Explain, using electronic structure, why neon does not react with other elements.

MODEL ANSWER

(1) Neon has a full outer electron shell (8 electrons).

(1) It does not need to gain, lose, or share electrons, so it doesn't form bonds.

Q4 — Transition metals vs Group I [4 marks]

EXAM-STYLE QUESTION [4 MARKS]

Give four differences between the properties of iron (a transition metal) and sodium (a Group I metal).

MODEL ANSWER

(1) Iron has a much higher melting point than sodium.

(1) Iron forms coloured compounds; sodium compounds are white or colourless.

(1) Iron has variable oxidation states (+2 and +3); sodium only forms +1 ions.

(1) Iron does not react with cold water; sodium reacts very vigorously.

Q5 — Period 3 oxide trend [3 marks]

EXAM-STYLE QUESTION [3 MARKS]

Describe how the type of oxide changes across Period 3 from sodium to chlorine.

MODEL ANSWER

(1) Sodium and magnesium oxides are basic — they dissolve to form alkaline solutions.

(1) Silicon's oxide is amphoteric — it reacts with both acids and alkalis.

(1) Phosphorus, sulfur, and chlorine oxides are acidic — they dissolve to form acidic solutions.

Q6 — Mendeleev's gaps [2 marks]

EXAM-STYLE QUESTION [2 MARKS]

Explain why Mendeleev left gaps in his periodic table and why this was significant.

MODEL ANSWER

(1) He predicted undiscovered elements would fill the gaps, using patterns in the properties of known elements.

(1) He predicted their physical and chemical properties — when gallium and germanium were discovered, they matched his predictions.

What exam mistakes cost the most marks?

Six errors that separate a Grade 5 from a Grade 7 in Topic 8.

Writing "atom gets bigger" without linking to shells, shielding, and nuclear attraction
Saying Group VII reactivity increases going down the group — it decreases
Confusing groups (vertical, same outer electrons) with periods (horizontal, same shells)
Missing state symbols in Group I equations, especially (aq) for metal hydroxides
Calling noble gases stable "because they're unreactive" — circular, scores zero
Saying a less reactive halogen displaces a more reactive one from solution

Must-know checklist before your IGCSE exam

Tick each point you're confident on. Any box you skip is a section to revisit first.

Group = vertical column. Period = horizontal row.
4-step trend chain: shells → distance → shielding → nuclear attraction
Group I: reactivity increases going down. Group VII: reactivity decreases going down.
Noble gases: full outer shell, monatomic, uses of He / Ne / Ar
Transition metals: coloured compounds, variable oxidation states, catalysts
Period 3 oxide trend: basic → amphoteric (Si) → acidic

Frequently asked questions

Is the periodic table given in the IGCSE exam?

Yes. CIE provides it in every 0620 paper. You still need to use it: apply trends, write equations, and explain reasoning. The table shows position; you supply the logic.

What if I mix up a group trend and a period trend?

Restate the direction at the start of your answer: "Going down Group I..." That confirms direction before you explain it. Examiners can't penalise you for clearly restating the question.

Which element symbols do I need to memorise?

For Group I: Li, Na, K. For Group VII: F, Cl, Br, I. For Group 0: He, Ne, Ar. For transition metals: Fe, Cu, Zn, Mn. Everything else is on the CIE data sheet.

How many marks does the periodic table carry in CIE 0620?

Topic 8 covers 10 to 15 percent of total paper marks. Trend questions alone carry 4 to 8 marks per paper. The same logic chain scores full marks every time once you know the four steps.

Related revision guides and tutoring support

Book an IGCSE tutor for one-to-one sessions covering the full CIE 0620 syllabus.
Subject-specific sessions: online Chemistry tutors cover all Topic 8 exam questions with mark-scheme focus.
Also studying Physics? IGCSE Physics tutors cover atomic structure and electron shells in parallel.
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In Abu Dhabi? Chemistry tutors in Abu Dhabi are available for CIE 0620 preparation.
Sitting O Level Chemistry? See our O Level tutors and the dedicated
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