OCR AS LEVEL CHEMISTRY A
1.1.1 ATOMS
1.2.1 ELECTRON STRUCTURE
1.3.1 PERIODICITY (a) – (d)
TEST
Answer all questions
Max 47 marks
Name ……………………………………………………………..
Mark ……../47 ……....% Grade ………
1. Carbon is in the p-block of the Periodic Table. Naturally occurring carbon
contains a mixture of two isotopes, 12C and 13C.
12
Complete the table below for the atomic structure of the isotopes C and 13C.
isotope protons neutrons electrons
12
C
Paddington Academy 1
13
C
[Total 2 marks]
2. Carbon occurs in a wide range of compounds and is essential to living systems.
Two isotopes of carbon are 12C and 13C.
(i) State what is meant by the term isotopes.
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(ii) Isotopes of carbon have the same chemical properties.
Explain why.
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(iii) The 12C isotope is used as the standard measurement of relative masses.
Define the term relative isotopic mass.
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[Total 4 marks]
Paddington Academy 2
3. A sample of carbon was found to contain 95% of 12C and 5% of 13C.
(i) The 13C isotope has a relative isotopic mass of 13.00.
Define the term relative isotopic mass.
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(ii) Calculate the relative atomic mass of this sample of carbon to three
significant figures.
Ar = ............................................
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[Total 4 marks]
4. Magnesium exists naturally as a mixture of its isotopes, 24Mg, 25Mg and 26Mg.
The isotopes in magnesium can be separated by mass spectrometry. The
diagram below shows a mass spectrometer.
(i) Complete the table below to show the composition of the 25Mg and 26Mg
isotopes.
protons neutrons electrons
25
Mg
26
Mg
[2]
(ii) Complete the electronic configuration of an atom of 24Mg.
1s2 .................................................................................................................
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[1]
Paddington Academy 3
(iii) Results from the mass spectrum of a sample of magnesium are shown
below.
isotope 24 25 26
Mg Mg Mg
relative isotopic
24.00 25.00 26.00
mass
% abundance 78.60 10.11 11.29
Calculate the relative atomic mass of the sample of magnesium.
Give your answer to two decimal places.
answer ...............................
[2]
[Total 5 marks]
5. The electronic configuration of a bromine atom can be written in terms of sub-
shells.
(i) Complete the electronic configuration of a bromine atom.
1s22s22p63s23p6 ...........................................................................................
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[2]
(ii) Why is bromine classified as a p-block element?
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[Total 3 marks]
Paddington Academy 4
6. The Periodic Table is a table of elements arranged in order of atomic number.
The elements are classified into blocks.
(i) State what is meant by the term atomic number.
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(ii) Complete the full electron configuration for a titanium atom.
1s2 ................................................................................................................
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[1]
(iii) Identify the seventh element in the fourth period.
State which block this element is in.
element ................................................
block .................................................
[1]
[Total 3 marks]
7. In their reactions, calcium and strontium each lose electrons to form ions with a
2 charge. The first and second ionisation energies of calcium and strontium
are shown below.
1st ionisation energy 2nd ionisation energy
/ kJ mol–1 / kJ mol–1
calcium 590 1145
strontium 550 1064
(i) Write an equation, with state symbols, to represent the second ionisation
energy of calcium.
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[2]
(ii) Why are the second ionisation energies of calcium and strontium greater
than their first ionisation energies?
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Paddington Academy 5
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Paddington Academy 6
(iii) Explain why the first and second ionisation energies of strontium are less
than those of calcium.
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[Total 6 marks]
8. This question refers to the elements in the first four periods of the Periodic
Table.
He
Ionisation energies provide information about the model for the electron
structure of elements.
(i) Explain why first ionisation energies show a general increase across
Period 3, Na–Ar.
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Paddington Academy 7
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(ii) Write an equation, including state symbols, to represent the third ionisation
energy of sodium.
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(iii) Element X is in Period 3 of the Periodic Table, Na–Ar.
The first six ionisation energies of an element X are shown below.
ionisation
1st 2nd 3rd 4th 5th 6th
number
ionisation energy
789 1577 3232 4 556 16091 19 785
/kJ mol–1
Predict, with reasons, the identity of element X.
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Paddington Academy 8
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[2]
[Total 6 marks]
Paddington Academy 9
9. The diagram below shows the variation in the first ionisation energies of
elements across Period 2 of the Periodic Table.
2500
Ne
2000
F
first ionisation N
1500
energy
/ kJ m ol –1 Be C O
1000
Li B
500
0
3 4 5 6 7 8 9 10
atom ic num ber
(i) Define the term first ionisation energy.
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(ii) Explain why the first ionisation energies show a general increase across
Period 2.
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(iii) Explain why the first ionisation energy of B is less than that of Be.
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Paddington Academy 10
[Total 7 marks]
Paddington Academy 11
10. Barium, Ba, was discovered by Davy in 1808. The element gets its name from
the Greek ‘barys’ meaning ‘heavy’.
The table below compares some properties of barium with caesium.
element Cs Ba
group 1 2
atomic number 55 56
atomic radius / pm 531 435
(i) Why do caesium and barium have different atomic numbers?
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(ii) State the block in the Periodic Table in which caesium and barium are
found.
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(iii) Explain why the atomic radius of barium is less than the atomic radius of
caesium.
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(iv) Predict and explain whether a barium ion is larger, smaller or the same
size as a barium atom.
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Paddington Academy 12
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[2]
[Total 7 marks]
Paddington Academy 13
