Ionic bonds are formed when one participant loses electron/s (and becomes a positively charged ion known as cation) and another gains it (or them, and becomes negatively charged ion called as anion). For example, in sodium chloride, sodium loses an electron and chlorine gains it and we get an ionic compound.
The complete transfer of electrons between atoms results in very strong interactions and it takes a great deal of energy to break such bonds. This means that ionic compounds have very high melting and boiling points. For example, sodium chloride has a melting point of 801 degree Celsius and a boiling point of 1413 degree Celsius. Similarly, when dissolved in water, the ions dissociate and are capable of conducting electricity (note that as a solid, ionic compounds will not conduct electricity). Ionic compounds form crystals due to strong interactions between participating ions and hence are also brittle, not malleable, when pressure is applied.
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