This question compares the bonding, structure and properties of sodium and sodium oxide

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This question compares the bonding, structure and properties of sodium and sodium oxide. (a) Sodium, Na, is a metallic element. Explain, with the aid of a labelled diagram, what is meant by the term metallic bonding. (b) Sodium reacts with oxygen to form sodium oxide,
, which is an ionic compound. (i) Write the equation for the reaction of sodium with oxygen to form sodium oxide. (ii) State what is meant by the term ionic bond. (iii) Draw a ‘dot-and-cross’ diagram to show the bonding in
. Show outer electrons only (c) Compare and explain the electrical conductivities of sodium and sodium oxide in the solid and liquid states.

The Correct Answer and Explanation is:

(a) Metallic Bonding (with Diagram)
Explanation:
Metallic bonding occurs in metals like sodium, where atoms lose their outermost electrons to form a structure of positive metal ions in a ‘sea’ of delocalized electrons. These free electrons move throughout the structure, holding the metal ions together by electrostatic attraction.

Labelled Diagram:

perlCopyEditNa+   Na+   Na+   Na+  
  \     |     /     |  
   e−  e−  e−  e−   (delocalized electrons)
  /     |     \     |  
Na+   Na+   Na+   Na+
  • Na+: Positive metal ions
  • e−: Delocalized electrons

(b) Sodium Oxide Formation

(i) Chemical Equation:
4Na+O2→2Na2O4Na + O_2 \rightarrow 2Na_2O4Na+O2​→2Na2​O

(ii) Ionic Bond Definition:
An ionic bond is the electrostatic force of attraction between oppositely charged ions. It forms when electrons are transferred from a metal to a non-metal.

(iii) Dot-and-Cross Diagram (showing outer electrons only):

Sodium ion (Na⁺): has no outer electrons
Oxide ion (O²⁻): gains two electrons to complete its octet

javascriptCopyEditNa⁺    Na⁺     :O:²⁻     Na⁺    Na⁺
          (with 8 electrons)
          [O with 4 dots (original) and 4 crosses (from Na)]

Example diagram (electron representation for O²⁻):

javaCopyEdit     ..
  : O :
     ''  ← 8 electrons around O (dots and crosses)

(c) Comparison of Electrical Conductivity

  • Sodium (Solid and Liquid):
    In both states, sodium conducts electricity. In the solid state, delocalized electrons move through the lattice, carrying charge. When melted, the mobile electrons still allow current to flow.
  • Sodium Oxide (Solid):
    In solid state, sodium oxide does not conduct electricity because ions are fixed in a crystal lattice and cannot move.
  • Sodium Oxide (Liquid or Aqueous):
    In molten or aqueous state, sodium oxide conducts electricity. The ions are free to move and carry electrical current.

Explanation Summary:
The ability of sodium to conduct in both states is due to mobile electrons. In contrast, sodium oxide conducts only when molten or dissolved, due to the mobility of ions rather than electrons.

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