Overview

What you'll learn

Read behaviour from position. Use periods (= electron shells) and groups (= valence electrons) to predict an element's valence, its ion charge and its reactivity.

Use trends. Track the patterns across a period and down a group — atomic radius, metallic character and reactivity.

Describe Group I, VII and VIII. Know the physical and chemical trends for the alkali metals, halogens and noble gases — plus the hallmarks of the transition metals.

Apply the reactivity series. Predict reactions with water, acid and salt solutions, match an extraction method to a metal, and explain rusting and how to prevent it.

Tutor's Insight

"A map for everything else."
These four subtopics are ones you'll lean on everywhere — every topic from 5 to 12 quietly relies on this, and it shows up as MCQ trend questions plus structured group and metal questions in Papers 1 and 2. Most questions don't ask you to recall facts — they ask you to predict from position. Knowing where an element sits tells you its valence, its likely ions, its reactivity, its colour. Anchor the trends. The rest follows.

8.1 The Periodic Table

8.1 The Periodic Table

What this subtopic asks of you
  • Read an element's behaviour from its position — periods = electron shells; groups = valence electrons; the charge of the ion follows.
  • Predict trends across a period and down a group — atomic radius, metallic character, reactivity, and ionisation in the right direction.

8.1 The Periodic Table

Arranged by proton number, read by row and column

Periods
The rows
A period number = the number of electron shells in the atom. Period 3 elements (Na → Ar) all have three shells; the next shell starts in Period 4.
Groups
The columns
A group number = the number of valence electrons (electrons in the outer shell). Group 1 has 1; Group 17 has 7; Group 18 has 8 (full).
Ion charge
Where the charge comes from
Atoms lose or gain electrons to reach a full outer shell. Groups 1/2/13 lose 1, 2, 3 e⁻; Groups 15/16/17 gain 3, 2, 1 e⁻.
Same group, same chemistry. Elements in the same group have the same number of valence electrons, so they form the same kind of ions and the same kind of bonds. Know sodium well and you have a head start on the rest of its group.

Free Notes · O-Level Pure Chemistry

Read the full chapter

Period and group trends, Group I, VII and VIII properties, halogen displacement, the transition-metal hallmarks, the reactivity series, metal extraction, rusting and 4 worked exam questions.

8.2 Group Properties

8.2 Group Properties

What this subtopic asks of you
  • Describe and explain three groups — Group I (alkali metals), Group VII (halogens), Group VIII (noble gases) — their physical and chemical trends.
  • Predict reactions from position — including halogen displacement — and explain why each trend goes the way it does.

8.2 Group Properties · Group I

Alkali metals — one outer electron, ready to go

Physical
Soft, light, low-melting
Cut with a knife. Lithium, sodium and potassium are less dense than water. Down the group: m.p. decreases; density mostly increases.
Stored
Under oil
Group I metals react with moisture and oxygen in air. Oil keeps them away from both. Freshly cut surfaces are shiny — but they tarnish in seconds.
Reactivity
Increases down the group
The outer electron is further from the nucleus going down — easier to lose. So K reacts more violently than Na, which reacts more violently than Li.
With water · the key reaction: 2M + 2H₂O → 2MOH + H₂↑ (M = Li, Na, K …). Li fizzes gently. Na melts into a ball, fizzes, can ignite. K bursts into a lilac flame. Cs explodes — strong enough to shatter glass. Same equation; different intensity.

8.2 Group Properties · Group VII

Halogens — seven outer electrons, hungry for one

Halogen Colour State at r.t. M.p. / b.p. (°C) Note
F₂ pale yellow gas −220 / −188 most reactive
Cl₂ yellow-green gas −101 / −34 —
Br₂ red-brown liquid −7 / 59 —
I₂ dark grey solid 114 / 184 least reactive
Halogen displacement. A more reactive halogen displaces a less reactive one from its salt — e.g. Cl₂ + 2NaBr → 2NaCl + Br₂. The Cl₂ takes the electrons; the colourless NaBr solution turns orange-brown as Br₂ forms. The order: F > Cl > Br > I.

8.2 Group Properties · Group VIII

Noble gases — already complete

Why they're inert
Full outer shell
He has 2 electrons (a full first shell). Ne, Ar, Kr, Xe, Rn all have 8 valence electrons. No electrons to lose, no room to gain — so they barely react.
Physical
Monatomic and colourless
All exist as single atoms — there's no driving force to bond, even to themselves. All colourless at room temperature; some glow with characteristic colours when excited (Ne — red-orange).
Where they show up
Inert atmospheres & lights
He — airships, weather balloons. Ne — neon signs. Ar — light bulbs (stops filament burning). Kr / Xe — flash photography, lasers.

8.3 Transition Elements

8.3 Transition Elements

What this subtopic asks of you
  • Spot a transition metal from its behaviour — high m.p., variable oxidation states, coloured compounds, catalytic activity.
  • Match catalysts to processes — iron in the Haber process, nickel in hydrogenation, Pt/Rh/Pd in catalytic converters.
Hallmark 01
High m.p. & density
Fe melts at 1538 °C; Cu at 1085. Strong metallic bonding from the d-electrons. Compare with Na at 98 °C.
Hallmark 02
Variable oxidation states
Iron forms Fe²⁺ (pale green) and Fe³⁺ (yellow-brown). Copper forms Cu⁺ and Cu²⁺. Same element, multiple ion-charges.
Hallmark 03
Coloured compounds
Cu²⁺ — blue. Fe²⁺ — green. Fe³⁺ — brown. Mn-containing compounds — purple / pink. Diagnostic in QA.
Hallmark 04
Often catalysts
Fe — Haber process (N₂ + 3H₂ → 2NH₃). Ni — hydrogenation of oils. Pt/Rh/Pd — catalytic converters in cars.
Exam Habit

Colour is a clue — if a structured or QA question mentions a green, blue or brown solution, reach for a transition-metal ion. The colour and the variable charge together often pin down exactly which ion is present.

8.4 The Reactivity Series

8.4 The Reactivity Series

What this subtopic asks of you
  • Order metals by ease of oxidation — and use that order to predict reactions with water, acid and the salts of other metals.
  • Extract a metal in the right way — electrolysis for the very reactive, carbon reduction for the rest — and know how to stop iron rusting.
K Na Ca Mg Al [C] Zn Fe Sn Pb [H] Cu Ag Au
More reactive Less reactive
With cold water
Stops at magnesium
K, Na, Ca — vigorous. Mg — very slowly. Below Mg — no reaction.
With dilute acid
Stops at lead
K, Na, Ca — too violent to test. Mg → Pb — react, faster the higher up. Cu and below — no reaction (below H).
Salt-solution displacement
Higher up wins
A more reactive metal displaces a less reactive one from its salt — e.g. Zn + CuSO₄ → ZnSO₄ + Cu. The blue solution fades and red-brown copper deposits.

8.4 The Reactivity Series · Extraction

Match the method to the metal

ORE → REDUCE BY THE RIGHT METHOD → METAL
Above carbon
Electrolysis only
K, Na, Ca, Mg, Al — too reactive to be reduced by carbon. Use electrolysis of the molten compound. Aluminium — bauxite (Al₂O₃) is melted with cryolite to lower the m.p. (cheaper).
Below carbon
Heat with carbon
Zn, Fe, Sn, Pb — carbon (or carbon monoxide) reduces the metal oxide. Iron in the blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
Below hydrogen
Often found native
Cu, Ag, Au — very unreactive, so they occur as the free metal in nature. Simple physical separation, with minor refining (e.g. electrolytic purification of Cu).

8.4 The Reactivity Series · Rusting

Iron needs both oxygen and water

What rust is
Hydrated iron(III) oxide
Fe₂O₃ · xH₂O. Iron rusts only when both O₂ and H₂O are present. Dissolved ions (salt) speed it up.
Why iron, not Al
The oxide doesn't protect
Aluminium's oxide layer is tough and stuck. Iron's rust flakes off, exposing fresh metal — so corrosion keeps going until the iron is gone.
Four ways to stop it

Barrier · Sacrificial · Galvanising · Alloying. Barrier — paint, oil, grease, plastic — keeps O₂ and H₂O away. Sacrificial — a more reactive metal (Zn) bolted on; it corrodes instead. Galvanising — a thin zinc coat: barrier AND sacrificial in one. Alloying — stainless steel (Fe + Cr + Ni) resists rust altogether.

Practice

Exam-style questions

Question 01  ·  AMKSS 2024 Prelim
The Question
MCQ

What the table can't tell you

Many properties of an element and its compounds can be predicted from the position of the element in the Periodic Table. Which property could not be predicted from the position of the element?

  • A  the number of isotopes the element has
  • B  the formula of the oxides of the element
  • C  the acidic and basic nature of the oxides
  • D  the metallic and non-metallic properties
Worked Answer
A
  1. B — formula of oxide comes from the valence (= group number). Predictable.
  2. C — acidic/basic nature: metal oxides basic, non-metal oxides acidic. Predictable.
  3. D — metallic vs non-metallic: left side metals, right side non-metals. Predictable.
  4. A — number of isotopes depends on neutron count, which the table doesn't show. NOT predictable. Answer A.
Question 02  ·  AMKSS 2024 Prelim
The Question
MCQ

X is liquid, Y is solid — what follows?

Elements X and Y are in Group 17. X is a liquid and Y is a solid at room temperature. Which statements are correct?

  • 1  — atoms of Y have more electrons than atoms of X
  • 2  — a molecule of Y has more atoms than a molecule of X
  • 3  — X displaces Y from an aqueous solution of Y⁻ ions

A 1 only    B 2 only    C 1 and 3 only    D 1, 2 and 3

Worked Answer
C — 1 and 3 only
  1. X must be bromine (Br₂, liquid); Y must be iodine (I₂, solid) — going down Group 17.
  2. Statement 1: Y is further down → more electrons. ✓
  3. Statement 2: all halogens are diatomic (X₂) → same number of atoms per molecule. ✗
  4. Statement 3: higher in the group = more reactive. Br₂ displaces I⁻: Br₂ + 2I⁻ → 2Br⁻ + I₂. ✓ Answer C.
Question 03  ·  AMKSS 2024 Prelim
The Question
MCQ

Ordering from a displacement table

Metals P, Q, R, S are placed in salt solutions. The results are:

  • • P displaces only S.
  • • Q displaces P and S.
  • • R displaces P, Q and S.
  • • S displaces nothing.

What is the order of the metals in increasing reactivity?

A Q, P, S, R    B R, Q, P, S    C S, P, Q, R    D S, Q, P, R

Worked Answer
C — S, P, Q, R
  1. A metal displaces only those less reactive than itself.
  2. S displaces nothing → S is least reactive.
  3. P displaces only S → P is just above S. Q displaces P (and S) → Q above P. R displaces all → R most reactive.
  4. Increasing reactivity: S < P < Q < R. Answer C.
Question 04
The Question
Structured

Extracting three metals

Aluminium, iron and copper are extracted from their ores by different methods. For each metal, state the method used and explain why that method is suitable, referring to the reactivity series.

Worked Answer
Position vs carbon decides the method
  1. Aluminium — above carbon in the series, so it is too reactive to be reduced by carbon. Extract by electrolysis of molten Al₂O₃ (dissolved in cryolite to lower the m.p. and cut cost).
  2. Iron — below carbon, so carbon (as CO) can reduce its oxide. Extract by heating with carbon in the blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂.
  3. Copper — below hydrogen and very unreactive, so it is found largely native and needs only physical separation plus electrolytic refining for purity.
  4. Rule: the more reactive the metal, the harder it is to reduce, so the more energy-intensive the extraction.

Frequently Asked Questions

Patterns in the Periodic Table — FAQ

What is Patterns in the Periodic Table in the O-Level Chemistry syllabus (6092)?
Patterns in the Periodic Table (Topic 8 of Syllabus 6092) covers four subtopics: 8.1 The Periodic Table — reading behaviour from position using periods, groups and ion charge; 8.2 Group Properties — the physical and chemical trends of Group I alkali metals, Group VII halogens and Group VIII noble gases; 8.3 Transition Elements — their four hallmarks and catalytic uses; and 8.4 The Reactivity Series — ordering metals and using that order to predict reactions, choose extraction methods and prevent rusting.
What is the difference between a period and a group in the Periodic Table?
A period is a row: the period number equals the number of electron shells, so all Period 3 elements (Na to Ar) have three shells. A group is a column: the group number tells you the number of valence electrons — Group I has 1, Group VII has 7, Group VIII has 8 (full, except helium with 2). Elements in the same group react the same way because they share the same number of valence electrons.
Why does reactivity increase down Group I but decrease down Group VII?
Going down a group, extra shells push the outer electrons further from the nucleus. Group I metals react by losing their one outer electron, so as it gets easier to lose going down, reactivity increases (K > Na > Li). Group VII react by gaining an electron, so as the outer shell moves further away it gets harder to attract one, and reactivity decreases (F most reactive, I least).
What is halogen displacement?
A more reactive halogen displaces a less reactive one from its salt solution. For example, Cl₂ + 2NaBr → 2NaCl + Br₂: the chlorine takes the electrons and the colourless sodium bromide solution turns orange-brown as bromine forms. The order of reactivity is F > Cl > Br > I.
What are the four hallmarks of a transition element?
Transition metals have (1) high melting points and densities from strong metallic bonding — Fe melts at 1538 °C versus Na at 98 °C; (2) variable oxidation states — Fe²⁺ and Fe³⁺, Cu⁺ and Cu²⁺; (3) coloured compounds — Cu²⁺ blue, Fe²⁺ green, Fe³⁺ brown; and (4) catalytic activity — iron in the Haber process, nickel in hydrogenation, Pt/Rh/Pd in catalytic converters.
How do you choose a metal extraction method using the reactivity series?
Compare the metal to carbon. Metals above carbon (K, Na, Ca, Mg, Al) are too reactive to be reduced by carbon, so extract them by electrolysis of the molten compound. Metals below carbon (Zn, Fe, Sn, Pb) are extracted by heating with carbon or carbon monoxide — e.g. Fe₂O₃ + 3CO → 2Fe + 3CO₂. Metals below hydrogen (Cu, Ag, Au) are so unreactive they occur native and need only physical separation and refining.

O-Level Pure Chemistry  ·  Syllabus 6092  ·  Topic 8 of 12  ·  © 2026 Overmugged. For personal study use only.