Question

How was ionic bonding discovered?

Answer 1

Ionic bonding or rather the concept of ionic bonding is one that revolves around the concept of charges and subatomic matter inside an atom whose excess or deficiency leads to generation of electrostatic interaction also called ionic interactions in a matter. It is a long-range force that can operate from a distance.

Complete step-by-step answer:
The year $1830$ was the fateful year when Sir Michael Faraday via his experiments on electrolysis showed that certain substances would conduct electricity when dissolved in water, He theorized that electricity might have caused the substances to break up into charged particles. The word ion was coined by Sir Michael Faraday which means wanderer in Greek, he is also the one who coined terms like cation and anion for the positive and negative particles.

In $1884$ ,Svante August Arrhenius reasoned that an ion is actually an atom carrying a positive or negative charge. He proposed that a compound like Sodium Chloride broke up into ions when dissolved in water, whether or not an electric current was present.

In $1887$, J.J. Thomson, another legendary scientist, showed that cathode rays were actually streams of electrons. He was the first to propose that electrons may be involved in some kind of bonding and even suggested that $HCl$ has atoms joined by a force which he preferred to call as a tube of electromagnetic force as the word bond was yet not christened. He suggested that $HCl$ had a positive and negative end.

By $1898$, Wilhelm Wein had shown that the $\dfrac{e}{m}$ratio of canal rays were proportional to the nature of gas used in the discharge tube. He also showed that positive charges unlike electrons could not be transferred from one atom to another and so could be involved in bonding. This was the beginning of the vast field of ionic bonding.

Note: Hence, in brief ionic bonding is a force of interaction that keeps atoms and molecules bound to each other via a force that is generated by some tweaks in the number of subatomic particles in an atom or a molecule, these subatomic particles are generally and most commonly electrons.