Periodic Table IGCSE Chemistry: Complete Revision Guide
Talimat Academic Team
Education Specialist
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.
CIE IGCSE Chemistry 0620: Periodic Table Guide
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.
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 are added going down.
- The outer electron sits further from the nucleus.
- More inner shells create greater shielding of outer electrons.
- Nuclear attraction on outer electrons weakens.
- Group I: outer e⁻ is lost more easily → reactivity INCREASES.
- Group VII: outer e⁻ is 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
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.
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.
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.
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.
About the author
Talimat Academic Team
Education Specialist
The Talimat Academic Team are Cambridge-trained British educators with extensive experience teaching IGCSE and A-Level across the GCC.
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