What are group properties in the context of the Periodic Table?

Group properties refer to the characteristics shared by elements within the same vertical column, or group, on the Periodic Table. These elements have similar chemical properties because they have the same number of valence electrons. Understanding group properties is crucial for predicting the behavior of elements in chemical reactions, which is a key concept in the Cambridge IGCSE Chemistry curriculum.

Why do elements in the same group of the Periodic Table exhibit similar chemical properties?

Elements in the same group of the Periodic Table exhibit similar chemical properties because they have the same number of valence electrons. This similarity in electron configuration leads to comparable reactivity and bonding characteristics. For example, the alkali metals in Group 1 all have one valence electron, making them highly reactive and similar in their chemical behavior.

How do the properties of Group 1 elements change as you move down the group?

As you move down Group 1 in the Periodic Table, the alkali metals become more reactive. This is due to the increasing atomic size and the decreasing ionization energy, which makes it easier for these elements to lose their single valence electron. Additionally, the melting and boiling points of these elements decrease down the group, which is an important trend to understand for the Cambridge IGCSE Chemistry exams.

What are the key differences between Group 1 and Group 7 elements in the Periodic Table?

Group 1 elements, known as alkali metals, are highly reactive metals with one valence electron, while Group 7 elements, known as halogens, are non-metals with seven valence electrons. Alkali metals tend to lose their single valence electron to form positive ions, whereas halogens gain an electron to form negative ions. These contrasting properties highlight the diversity of chemical behavior across the Periodic Table, a fundamental concept in Cambridge IGCSE Chemistry.

How do the properties of Group 0 elements differ from other groups in the Periodic Table?

Group 0 elements, also known as noble gases, are characterized by their lack of reactivity due to having a full valence shell of electrons. This makes them stable and unlikely to form compounds under normal conditions. Unlike other groups, noble gases do not readily gain or lose electrons, which is why they are often used in applications where non-reactivity is essential. Understanding these unique properties is important for students studying the Periodic Table in the Cambridge IGCSE Chemistry curriculum.

Why is "Saying alkali metals are stored in water" a common mistake in Group Properties?

Why it happens: Confusing storage media. How to avoid it: Stored under OIL — they react with water! Source: 0620/42 — recurring

Why is "Saying iodine is a brown liquid" a common mistake in Group Properties?

Why it happens: Confusing with bromine. How to avoid it: Cl: gas. Br: liquid. I: solid.

Why is "Forgetting the 2 in $2\text{Na} + 2\text{H}_{2}\text{O}$" a common mistake in Group Properties?

Why it happens: Speed. How to avoid it: Two Na atoms produce two OH groups + one H_2 molecule.

The Periodic TableCambridge IGCSE Chemistry (0620)

Group Properties

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Group 1 and Group 17 Properties — Cambridge IGCSE 0620 Chemistry Extended (2026)

The classic two groups: alkali metals (very reactive, soft, low-density) and halogens (coloured, diatomic, displacement reactions). Detailed examples and trends.

What you’ll learn

Mapped to the Cambridge IGCSE 0620 syllabus (2026-2028).

10.3 — Describe the properties of Group 1 elements: physical and reactivity.
10.3 — Write equations for Group 1 + water.
10.4 — Describe the properties and reactions of Group 17 elements.
10.4 — Describe halogen displacement.

Group 1 — alkali metals

Soft, low-density, very reactive metals. Reactivity rises down the group.

Physical properties.

Silvery shine when cut, but TARNISH quickly in air (oxide layer forms).
SOFT — can be cut with a knife.
LOW density — Li, Na, K all float on water.
LOW melting point — caesium melts in your hand (m.p. $28\degree\text{C}$ ).
Good conductors of heat and electricity.

Reaction with water. All Group 1 metals react with cold water: $2\text{Na} + 2\text{H}_{2}\text{O} \to 2\text{NaOH} + \text{H}_{2}.$

The product is a strongly alkaline metal hydroxide solution + hydrogen gas.

Vigour increases down the group.

Lithium: floats, fizzes slowly, gives off H₂.
Sodium: floats, melts into a ball (heat from reaction), darts around the surface, fizzes vigorously.
Potassium: ignites the H₂ produced — lilac flame.
Rubidium and caesium: explosive (Cs typically dropped through the water surface).

Why down the group is more reactive. Larger atom → outer e⁻ further from nucleus → weaker hold → easier to lose → more reactive. (See Periodic Trends.)

Reaction with halogens. $2\text{Na} + \text{Cl}_{2} \to 2\text{NaCl}$ — dramatic, white solid forms.

Reaction with oxygen. Tarnish in air; on heating burn brightly.

$4\text{Na} + \text{O}_{2} \to 2\text{Na}_{2}\text{O}$ .

Cambridge tip. When predicting properties of Fr (francium, Group 1), say "more reactive than Cs, even softer, even lower m.p." (extrapolate the trend).

Soft, low density, low m.p., shiny.
React with water → MOH + H₂.
Reactivity: Cs > Rb > K > Na > Li.
More reactive down — bigger atom, easier to lose e⁻.

Group 17 — halogens

Coloured diatomic non-metals. Reactivity decreases down the group. Displacement reactions follow.

Physical properties. All exist as DIATOMIC molecules (F₂, Cl₂, Br₂, I₂).

Halogen	Formula	Room-T state	Colour	b.p.
Fluorine	F₂	Gas	Pale yellow	$-188\degree\text{C}$
Chlorine	Cl₂	Gas	Pale yellow-green	$-34\degree\text{C}$
Bromine	Br₂	LIQUID	Red-brown	$59\degree\text{C}$
Iodine	I₂	SOLID	Grey-purple	$184\degree\text{C}$

Down the group:

Colour deepens.
m.p. and b.p. increase.
State changes: gas → liquid → solid.
Reactivity DECREASES.

Why m.p. rises down the group. Bigger atoms → more electrons → stronger intermolecular (van der Waals) forces between diatomic molecules → harder to overcome → higher m.p./b.p.

Why reactivity decreases down the group. Bigger atoms → outer shell further from nucleus → harder to attract incoming electron → less reactive.

Reaction with metals. Halogens react vigorously with metals to form salts (halides). $2\text{Na} + \text{Cl}_{2} \to 2\text{NaCl}.$ $\text{Mg} + \text{Cl}_{2} \to \text{MgCl}_{2}.$

Reaction with hydrogen. $\text{H}_{2} + \text{Cl}_{2} \to 2\text{HCl}$ .

F₂ + H₂: explosive even in dark.
Cl₂ + H₂: explosive in sunlight.
Br₂ + H₂: needs catalyst.
I₂ + H₂: slow, reversible.

Diatomic, coloured, non-metals.
Down: deeper colour, higher m.p./b.p.
Down: less reactive.
React with metals → salts.

Halogen displacement reactions

More reactive halogen displaces less reactive halogen from a halide salt.

Rule. A more reactive halogen DISPLACES a less reactive halogen from a salt of that halide.

Worked. Add chlorine water to potassium bromide solution: $\text{Cl}_{2} + 2\text{KBr} \to 2\text{KCl} + \text{Br}_{2}.$

Chlorine is more reactive than bromine.
It DISPLACES bromine from the bromide.
Solution turns red-brown (colour of Br₂).

Worked. Add bromine water to potassium iodide: $\text{Br}_{2} + 2\text{KI} \to 2\text{KBr} + \text{I}_{2}.$

Bromine displaces iodine.
Solution turns dark / brown-purple (I₂).

No reaction. Iodine + KCl → no displacement (I is less reactive than Cl).

Use of displacement. Confirms the order of reactivity F > Cl > Br > I, and is used as a test for halide ions.

Cambridge tip. Always state the colour change of the solution as evidence of the displacement.

More reactive halogen displaces less reactive.
Cl displaces Br and I.
Br displaces I.
I displaces nothing in Group 17.
Colour change confirms.

How it’s examined

Group 1 and 17 properties appear every Paper 4 (5-7 marks): predict reactions, explain trends. Examiner reports flag students confusing the direction of the reactivity trend (it's INCREASING down for G1, DECREASING down for G17).

Sources: Cambridge IGCSE Chemistry 0620 syllabus 2026-2028 (10.3-10.4); 0620/22 May/Jun 2024 — Q12 (Group 1 + Group 17); 0620 Examiner Reports 2022-2024. Last reviewed 2026-05-07.

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Step-by-step worked examples — Group Properties

Step-by-step solutions to past-paper-style questions on group properties, written exactly the way a tutor would explain them at the board.

1Group I + water
Core• Group I
Question
Write the equation for sodium reacting with water.
Step-by-step solution
1. Step 1
  Group I + water → metal hydroxide + hydrogen.
  $2\text{Na} + 2\text{H}_{2}\text{O} \to 2\text{NaOH} + \text{H}_{2}$
Answer
$2\text{Na} + 2\text{H}_{2}\text{O} \to 2\text{NaOH} + \text{H}_{2}$
2Why alkali metals are stored under oil
Core• Adapted from 0620/22 May/Jun 2024 Q12• Group I
Question
Explain why sodium is stored under oil.
Step-by-step solution
1. Step 1
  Sodium reacts with water vapour AND oxygen in the air.
2. Step 2
  Oil prevents contact with both → keeps the metal pure.
Answer
Oil prevents contact with air and moisture, both of which react with sodium.
3Physical states of halogens
Core• Group VII
Question
State the physical state of chlorine, bromine and iodine at room temperature.
Step-by-step solution
1. Step 1
  Chlorine: pale yellow-green GAS.
2. Step 2
  Bromine: red-brown LIQUID.
3. Step 3
  Iodine: dark grey/violet SOLID (sublimes to violet vapour).
Answer
Cl: gas, Br: liquid, I: solid (at room temperature).
4Test for halide ions
Extended• test
Question
Describe the test for chloride, bromide and iodide ions.
Step-by-step solution
1. Step 1
  Acidify with dilute nitric acid then add aqueous silver nitrate.
2. Step 2
  Cl⁻: WHITE precipitate. Br⁻: CREAM precipitate. I⁻: YELLOW precipitate.
Answer
AgNO₃ + dilute HNO₃ → white (Cl), cream (Br), yellow (I).

Key Definitions and Keywords — Group Properties

Definitions to memorise and the exact keywords mark schemes credit for group properties answers — sharpened from recent examiner reports for the 2026 0620 sitting.

Alkali metals (Group I)
Examiner keyword
Soft, low-density, highly reactive metals (Li, Na, K, Rb, Cs). Form +1 ions.
Halogens (Group VII)
Examiner keyword
Highly reactive non-metals existing as DIATOMIC molecules ( $\text{X}_{2}$ ). Form $-1$ ions.
Noble gases (Group 0/VIII)
Examiner keyword
Unreactive monatomic gases with full outer shells.

Common Mistakes and Misconceptions — Group Properties

The traps other students keep falling into on group properties questions — taken from recent Cambridge IGCSE 0620 examiner reports and mark schemes — and how to avoid them.

✕Saying alkali metals are stored in water
0620/42 — recurring
Why it happens
Confusing storage media.
How to avoid it
Stored under OIL — they react with water!
✕Saying iodine is a brown liquid
Why it happens
Confusing with bromine.
How to avoid it
Cl: gas. Br: liquid. I: solid.
✕Forgetting the 2 in $2\text{Na} + 2\text{H}_{2}\text{O}$
Why it happens
Speed.
How to avoid it
Two Na atoms produce two OH groups + one $\text{H}_{2}$ molecule.

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