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The table shows the elements in period 3 of the periodic table. Study it and answer the questions that follow.

 Element Na  Mg  Al  Si  P  S  Cl  Ar 

  1. Write the formulae of two oxides, for each of the following
    • sodium:   
      • Oxide I
      • Oxide II
    • chlorine 
      • Oxide I
      • Oxide II
  2. The products of the reaction between phosphorus and chlorine depend on the conditions used. Write the equation for the reaction when chlorine reacts with excess phosphorus. 
  3. Identify the element with the highest electrical conductivity. Give a reason.  
  4. Describe an experiment that can be used to illustrate the variations in reaction of sodium, magnesium and aluminium with water.  
  5. State and explain the differences in the melting points of:
    • Chlorine and argon.   
    • magnesium oxide and silicon(IV) oxide. 

1 Answer

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    • Sodium
      • Oxide I - Na2O
      • Oxide II   Na2O2
    • Chlorine 
      • Oxide I     Cl2O        
      • Oxide II Cl2O 
        (ClO, ClO2, Cl2O2, Cl2O5, Cl2O6, Cl2O, ClO3)
    • 2P(s) + 3Cl2(g) → 2PCl3(l) ✓1
      P4(s) + 6Cl2(g) → 4PCl3(g)  ✓1
      P10(s) + 15Cl2(g) → 10PCl3(g)  ✓1
  3. Al (Not Al3+).  
    • Highest number of delocalised electrons/highest number of valence electrons per atom
    • has 3 delocalised electrons per atom.
  4. ​​​​​​​  
    • Sodium reacts vigorously with water/hissing sound is produced
    • Magnesium reacts slowly with water/produces few bubbles on the surface.
    • Aluminium does not react with water/produces no bubbles. 
      • Melting point of chlorine is greater/higher than that of argon. Cl2(g) is diatomic while Ar(g) is monoatomic hence Cl2(g) has stronger vanderwaals. 
      • Forces of attraction/molecules of Cl2(g) are larger/bigger than Ar(g) molecules hence intermolecules forces in Cl2 are stronger than Ar.
    • Magnesium oxide has a higher melting than Silicon (IV) Oxide.

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