Exam-style Questions: Atomic Structure

1. Chemists use a model of an atom that consists of three types of sub-atomic particle. These are protons, neutrons and electrons.

a) Complete the table below, which shows the properties of these particles.

Particle

Relative Charge

Relative Mass

Electron

Proton

1

Neutron

0

(4 marks)

b) Types of atoms and ions vary from each other by the number of sub-atomic
particle found in them. What differences are there between 12C and
14C?

(1 mark)

c) Define the term 'isotope'.

(1 mark)

d) Write down the electronic configuration of Cr3+.

(1 mark)

(Marks available: 7)

Answer

Answer outline and marking scheme for question: 1

a)

Particle

Relative Charge

Relative Mass

Electron

-1

1/1820 or negligible

Proton

+1

1

Neutron

0

1

(4 marks)

b) 12C has 6 protons, 6 neutrons and 6 electrons. 14C
has 6 protons, 6 electrons and 8 neutrons. The difference between this pair
is that 14C has two more neutrons than 12C.

(1 mark)

c) An isotope of an element has he same number of protons but a different
number of neutrons.

(1 mark)

d) 1s2 2s2 2p6 3s2 3p6
3d3 4s0

(1 mark)

(Marks available: 7)

2. a) The first ionisation energy for lithium is 519 kJmol-1.

Write an equation to show what is meant by this statement.

(1 mark)

b) The second ionisation energy for lithium is 7300 kJmol-1.
Explain the difference in value for the first and second ionisation energy for
lithium.

(1 mark)

(Marks available: 2)

Answer

Answer outline and marking scheme for question: 2

a) Li(g) - e- = Li+(g)



The electronic configuration of lithium is 1s2 2s1. It
is relatively easy to remove the electron from the 2s orbital as it is shielded
from the nuclear charge by the 1s electrons.

(1 mark)

b) To remove the second electron for the second ionisation energy requires
considerably more energy as this electron comes from the 1s shell which is closer
to the nucleus and not subject to any shielding.

(1 mark)

(Marks available: 2)