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Question

What is the coordination number of Sodium in Sodium Oxide?


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Solution

Coordination number:

  • The number of particles that surround a single particle in a crystal lattice is known as the coordination number of that particle.

Sodium oxide:

  • Sodium oxide Na2Ois an example of Face Centred Cubic crystal structure.
  • The coordination number of both the ions in a compound may or may not be the same.

The coordination number of sodium in sodium-ion:

  • Sodium-ion takes up the tetrahedral void in the lattice and oxide ion takes up all the corners of the FCC.
  • In sodium oxide Na2O, Na+ ions are present at tetrahedral voids and O2 ions occupy half of the cubic holes in the face cubic close lattice. Na+ions are present at body diagonals.
  • One corner sphere and three face spheres combine to produce a tetrahedral void in an FCC structure. Two tetrahedral voids and one cube diagonal are obtained in an FCC structure. One unit cell contains a total of four cube diagonals. As a result, an FCC structure has eight tetrahedral voids overall.
  • Each sodium ion is surrounded by 4 oxide ions and each oxide ion is surrounded by 8 sodium ions.
  • Thus, the number of sodium ions in one unit cell (FCC) = 8x1=8
  • Number of oxide ions in one unit cell (FCC) = 8x1/8+(6x1/2)=4, as there are 8 corners and 6 faces

Thus, as one sodium ion is surrounded by 4 oxide ions, the coordination number of sodium in Sodium oxide is 4.


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