CAIE IGCSE Chemistry Isotopes Question Bank

Practise identifying isotopes from particle data, explaining their shared chemical behaviour and calculating relative atomic mass from abundance data.

Exam points

identify isotopes as atoms with the same proton number but different numbers of neutrons
complete isotope particle tables and explain similar chemistry through equal outer-shell configurations
calculate relative atomic mass as a weighted mean from isotopic masses and abundances

Covered syllabus points

2.3.1—Isotopes as different atoms of the 2.3.2—Symbols for atoms and ions 2.3.3—Isotopes of the same element have the 2.3.4—Relative atomic mass of an element

[Maximum number: 5]

This question is about elements X, Y and Z.

(a)

An atom of element X is represented as ${ }_{16}^{34} \mathbf{X}$ .

[ 1 ]

(i)

What is the total number of particles in the nucleus of an atom of ${ }_{16}^{34} \mathbf{X}$ ?

[ 1 ]

(b)

What term is used to describe atoms of the same element with different numbers of particles in the nucleus?

[ 1 ]

(c)

Part of the definition of relative atomic mass is 'the average mass of naturally occurring atoms of an element'.

Some relative atomic masses are not whole numbers.
Element Y has only two different types of atom, ${ }^{69} \mathbf{Y}$ and ${ }^{71} \mathbf{Y}$ .
The ratio of atoms present in element Y is shown.

{ }^{69} \mathbf{Y}:{ }^{71} \mathbf{Y}=3: 2

- Calculate the relative atomic mass of element Y to one decimal place.
relative atomic mass =
- Identify element Y.

[ 3 ]

$\text { M1 }(3 \times 69)+(2 \times 71)$ $\mathrm{M} 2=\frac{349}{5}=69.8$

M3 Y=Ga / gallium

[Maximum number: 5]

Sulfur is a Group VI element.

(a)

A sample of sulfur contains two isotopes, ${ }^{32} \mathrm{~S}$ and ${ }^{34} \mathrm{~S}$ .

[ 5 ]

(i)

Complete Table 5.1 to show the number of protons and neutrons in one atom of each isotope of sulfur.

Table 5.1

[ 2 ]

& ${ }^{32} \mathrm{~S}$ & ${ }^{34} \mathrm{~S}$

protons & 16 & 16

neutrons & 16 & 18

(ii)

State why these isotopes have identical chemical properties.

[ 1 ]

(iii)

Table 5.2 shows the relative abundance of these isotopes of sulfur in the sample.

Table 5.2

Calculate the relative atomic mass of sulfur in this sample to one decimal place.
relative atomic mass =

[ 2 ]

$\mathrm{M} 1(32 \times 95)+(34 \times 5)=3210$

M2 3210 / 100=32.1

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Covered syllabus points

2.3 Isotopes question 1

Question (a)

Question (i)

Question (b)

Question (c)

2.3 Isotopes question 2

Question (a)

Question (i)

Question (ii)

Question (iii)