A LevelChemistryCIETopic Questions9. The Periodic Table: Chemical Periodicity9.2 Periodicity of Chemical Properties of the Elements in Period 3

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First exams 2025

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

Topic Questions

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1a3 marks

The melting points of some of the oxides of the Period 3 elements, sodium to sulfur, are given in Table 2.1

Table 2.1

Compound Melting point / K
Na2O 1193
MgO 3173
Al2O3 2313
SiO2 1883
P4O10 613
SO2 198

State what is broken when each of the following compounds is melted.

Na2O .............................................................................................................
SiO2 .............................................................................................................
P4O10 .............................................................................................................

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1b3 marks
i)
Give the formula of a Period 3 oxide from Table 2.1 that reacts with water to produce a hydroxide.

[1]

ii)
Give the formula of a Period 3 oxide from Table 2.1 that reacts with water to produce an acid.

[1]

iii)
Give the formula of a Period 3 oxide from Table 2.1 that has no reaction at all with water.

[1]

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1c3 marks

The oxides of the elements of the third Period behave differently with NaOH (aq) and HCl (aq). In some cases, no reaction occurs.

Complete Table 2.2 by writing 'reaction' for any reaction that occurs between the Period 3 oxide and HCl (aq) or NaOH (aq), with heating if necessary. If you think no reaction takes place write ‘no reaction’.

Table 2.2

 Period 3 oxide With HCl (aq) With NaOH (aq)
MgO (s)    
Al2O3 (s)    
SO2 (g)    

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2a4 marks

Period 3 elements react with chlorine to form chlorides.

i)
Give the equation to show the reaction when aluminium is heated with chlorine to form aluminium chloride, Al2Cl6.

[1]

ii)
Complete Table 3.1 to show the oxidation number of the Period 3 elements in the chloride with the formula given in the table.

Table 3.1

Period 3 element Formula of chloride Oxidation number of Period 3 element in the chloride
Na NaCl  
Mg MgCl2  
Al Al2Cl6  
Si SiCl4  
P PCl5  
S SCl2  

[3]

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2b2 marks
i)
State what would be seen when MgCl2 is added to water.

[1]

ii)
Suggest the pH of the resulting solution.

[1]

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2c3 marks

Liquid silicon chloride, SiCl4, and solid phosphorus(V) chloride, PCl5, can be hydrolysed in water, both reactions produce acidic solutions and release white fumes.

Give the balanced symbol equation for the reaction of phosphorus(V) chloride with water. Include state symbols.

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1a6 marks

Sodium oxide and sulfur dioxide are separately added to water.

 

Write equations for and observations of each reaction and state the pH of any solution formed.

 
  • Sodium oxide and water
    ..............................................................................................................
  • Observations
    .............................................................................................................. 
  • Resulting pH
    ..............................................................................................................
     
  • Sulfur dioxide and water
    ..............................................................................................................
  • Observations
    ..............................................................................................................
  • Resulting pH
    ..............................................................................................................

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1b1 mark

A concentrated solution of the compound produced when sodium oxide is added to water is heated with silicon dioxide.

 

Write the ionic equation for this reaction.

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1c3 marks

Compound A is an oxide of a Period 3 element. It dissolves in hot, concentrated potassium hydroxide and in nitric acid, but it is insoluble in water. 

 
i)
State the term that is used to describe the behaviour of compound A. 
 
[1]
 
ii)
Write equations, including state symbols, for the reactions of compound A with potassium hydroxide and nitric acid. 
 
[2]

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2a3 marks

The acid-base character of the Period 3 oxides changes from sodium to sulfur.

In terms of electronegativity of the Period 3 element, explain why the acid-base character changes.

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2b5 marks

When phosphorus(V) oxide reacts with water it will produce phosphoric acid. 

 
i)
Write an equation to show the formation of phosphoric acid and include the expected pH of the resulting solution. 
 
[2]
 
ii)
Explain why the melting point of phosphorus(V) oxide is relatively low compared to most other Period 3 oxides.
 
[3]

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2c3 marks

Phosphorus(V) pentoxide reacts with sodium hydroxide solution, NaOH (aq), to form a phosphate salt. 

 
i)
Write the overall equation for this reaction, including state symbols.  
 
[1]
 
ii)
Using oxidation numbers, state whether the reaction is a redox reaction.  
 
[2]

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3a3 marks

Silicon(IV) chloride is formed by the reaction of silicon and chlorine.

i)
Write an equation for this reaction.
 
[1]
 
ii)
Draw the structure of silicon(IV) chloride.
 
[1]
 
iii)
Explain why silicon chloride is a liquid at room temperature.
 
[1]

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3b3 marks

The reaction of silicon(IV) chloride and water is very violent giving a white solid, silicon dioxide and steamy fumes of hydrogen chloride.

 
Tetrachloromethane gives no reaction with water.

 
Using your knowledge of electronic configuration, explain the difference between these two observations.

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3c2 marks
i)
Write an equation which demonstrates the acidic property of silicon dioxide.
 
[1]
 
ii)
Explain why silicon dioxide cannot act as a base.
 
[1]

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1a4 marks

Oxides are compounds which usually contain oxygen combined with one other element.

Oxides are classified as follows.

acidic alkaline amphoteric basic

Complete Table 2.1 to describe the oxides of the elements of the third period of the Periodic Table from sodium to sulfur.

Table 2.1

Na2O  MgO Al2O3 SiO2  P4O10 SO2 Cl2O7
             

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1b3 marks

Some of the oxides produced can react with water. 

i)
Write an equation for the reaction of each of these oxides with water.

Na2O ..........................................................................................................................................................................
SO2    ..........................................................................................................................................................................

[2]

ii)
What is the pH of the resulting solution in each case?

Na2O .....................................
SO2   .....................................

[1]

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1c2 marks

Give the oxidation number for the Period 3 element in each oxide.

Na2O ...................................
SO2   ...................................

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1d4 marks

The melting points of the two Period 3 oxides are displayed in Table 2.2. 

Table 2.2 

Na2O 1132 oC
SO2 -72 oC 


Explain the difference in melting points.

You should refer to the structure and bonding of each substance.

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2a2 marks

This question concerns the chlorides of the elements sodium to phosphorus of the third period of the Periodic Table.

The melting points of these chlorides are given below in Table 4.1

Table 4.1

compound Sodium chloride Magnesium chloride Aluminium chloride Silicon tetrachloride Phosphorus(V) chloride
melting point / K 1081 987 451* 203 435

*sublimes at 451 K

Give the equation, with state symbols, for the reaction of phosphorus with chlorine to form phosphorus(V) chloride, PCl5.

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2b4 marks

Suggest, in terms of the structure and bonding, explanations for the following.
You should draw diagrams where you think they will help your answer.
 

i)
The high melting point of sodium chloride
[2]
ii)
The low melting point of silicon tetrachloride
[2]

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2c1 mark

Write an equation for the reaction of silicon tetrachloride with water.

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2d2 marks

What is the pH of the solution formed when each of the following compounds is dissolved in water?

NaCl ........................................
PCl5 .........................................

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3a1 mark

Elements in the same period of the Periodic Table show trends in physical and chemical properties. 

The ionic radius for the Period 3 elements are in Table 5.1 

Table 5.1

  Na+ Mg2+ Al3+ Si4+ P3- S2- Cl-
 Ionic radius (nm) 0.095 0.065 0.050 0.041 0.212 0.184 0.181

Complete Fig 5.1 to show the variation in ionic radius of Period 3 elements. 

2-1-5a-m2-1-q5a-ionic-radius-graph-outline-a
Fig. 5.1

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3b5 marks
i)
Complete Fig. 5.2 to show the variation of electrical conductivity across Period 3.

2-1-5a-m-2-1-q5a-ionic-radius-graph-outline-a

Fig. 5.2

[2]

ii)
Explain your answer to part (i)

[3]

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3c2 marks

Period 3 elements can react with oxygen to form oxides. 

Some Period 3 elements can react with water. 

In the boxes below write the formulae of one of the oxides of each of these five elements.

sodium magnesium aluminium phosphorus sulfur
         

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3d3 marks

Explain why aluminium oxide is known as amphoteric. 

You should use equations in your answer. 

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