# How was ionic bonding discovered?

May 23, 2015

The idea of ionic bonding developed gradually over the years.

Around 1830, Michael Faraday's experiments on electrolysis showed that certain substances would conduct an electric current when dissolved in water.

He thought that the electricity caused the substances to break up into charged particles.

He introduced the term ion (wanderer in Greek) and invented the terms cation and anion for the positive and negative particles.

In 1884, Svante August Arrhenius reasoned that an ion is an atom carrying a positive or negative charge.

He proposed that a compound like sodium chloride broke up into ions when it dissolved in water, whether or not an electric current was present.

In 1897, J. J. Thomson showed that cathode rays were streams of free electrons.

He felt that electrons were somehow involved in bonding and even proposed that the atoms in HCl are joined by a "tube" of electromagnetic force (the word "bond" hadn't been invented yet).

He suggested that HCl had a positive and a negative end.

By 1898, Wilhelm Wien had showed that the $e \text{/} m$ ratio of canal rays depended on the gas in the discharge tube.

He showed that positive charges (unlike electrons) were not transferred from one atom to another and so could not be involved in bonding.

From that time on, theories of ionic bonding and the transfer of electrons developed rapidly.