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.

Explanation:

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"NaCl, a sodium ion has 6 chloride ions as nearest neighbours.

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

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

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

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

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