Syllabus Edition

First teaching 2023

First exams 2025

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Periodicity of Physical Properties of the Elements in Period 3 (CIE A Level Chemistry)

Topic Questions

1a1 mark

The elements across Period 3 show patterns in their chemical and physical properties.

State the trend in the atomic radius of successive elements in Period 3.

1b4 marks

The electrical conductivity of the elements in Period 3 varies across the period as shown in Fig. 1.1.

electrical-conductivity-answer

Fig. 1.1

i)
Explain why aluminium has a much higher electrical conductivity than sulfur. You should refer to the structure of both elements.

[2]

ii)
Explain why aluminium has a higher electrical conductivity than magnesium. 

[2]

1c6 marks

The melting points of three successive elements in Period 3 are shown in Table 1.1.

Table 1.1

Element Melting point / °C
Aluminium 660
Silicon 1410
Phosphorous 44

i)
Explain, referring to its structure and bonding, why the melting point of silicon is high.

[3]

ii)
Explain, referring to its structure and bonding, why the melting point of phosphorus is low.

[3]

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1a3 marks

The elements in Period 3 of the Periodic Table show variations in their behaviour across the period.

Fig. 3.1 shows the variation of melting points of the elements across Period 3.

2-1-3a-m-2-1-q3a-melting-point-graph

Fig. 3.1

In each of the following parts of this question you should clearly identify the interactions involved and, where appropriate, explain their relative magnitudes.

Explain the general increase in melting point from Na to Al.

1b3 marks

Explain the variation of melting points from P to Ar.

1c1 mark

Explain why Si has a much higher melting point than any of the other elements in the period.

1d5 marks

Going across Period 3, a trend in electronegativity can also be observed. 

i)
Define the term electronegativity. 

[2]

ii)
Complete Fig. 3.2 to show how electronegativity changes along Period 3. 
sDqDeh-e_2-1-3d-m-2-1-3d-electronegativity-graph
Fig. 3.2
[1]

iii)
Explain your answer to part (ii).
[2]

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2a5 marks

The properties of elements and their compounds show similarities, differences and trends depending on the positions of the elements in the Periodic Table.

i)
Define ionic radius.
 
[1]
 
ii)
Explain how ionic radius differs between cations and anions in terms of the parent atoms.
 
[4]
2b3 marks

On Fig. 2.1, sketch a graph to show the trend in the ionic radius of successive elements in Period 3. 

jp2rIVVx_blank-ionic-radius-graph

Fig. 2.1

2c3 marks

Explain the trend shown in part (b).

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3a3 marks

Table 3.1 shows the melting points and atomic radii of the elements in Period 3, Na to Cl.

Table 3.1

Element Na Mg Al Si P S Cl
Melting point / °C 98  649 660 1410 44 113 –101
Atomic radius / pm 186  160  143 118 110 102 99

Explain the difference in melting point for the elements Na and Mg.

3b4 marks

Explain why phosphorous has a lower melting point than sulfur.

3c4 marks

Explain the trend in atomic radius shown in Table 3.1 in part (a)

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