# Why is ionic bonding referred to as non directional?

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 $\text{NaCl}$, a sodium ion has 6 chloride ions as nearest neighbours.

The $\text{Na-Cl}$ "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 $\text{Cs-Cl}$ "bonds" are at different angles.

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

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