Why is ionic bonding referred to as non directional?

1 Answer
Apr 24, 2014

Ionic bonding is non-directional because an ion has the same attraction from all directions for an ion of opposite charge.


In the same way, a magnet attracts iron filings from all directions.

This means that packing efficiency in the crystal lattice determines the arrangement of ions in a crystal.

There is no preferred direction for the bonds.

Thus, in a crystal of #"NaCl"#, a sodium ion has 6 chloride ions as nearest neighbours.

The #"Na-Cl"# "bonds" are all at angles of 90° to each other.


In a crystal of cesium chloride, a cesium ion has eight chloride atoms as nearest neighbours.

The #"Cs-Cl"# "bonds" are at different angles.

The differences arise because #"Cs"^"+"# and #"Cl"^"-"# have almost the same ionic radii (about 170 pm) and pack in one arrangement.

A #"Na"^"+"# ion is smaller (116 pm) than #"Cl"^"-"#, so the ions pack in a different arrangement.