Salt

Salt (chemical name: sodium chloride - NaCl) is composed of ions, which are electrically-charged atoms formed when the elements sodium and chlorine bond.

During the reaction, the sodium atoms become positively-charged sodium ions (Na+) and the chlorine atoms become negatively charged chloride ions (Cl^-). Each sodium ion is surrounded by six chloride ions to form a perfect symetrical crystal. As opposites attract the bonds are very tight. If salt is heated to more than 800°C, the strong bond between the individual ions weakens and the crystal melts.

If salt is added to water, the water molecules push their way between the ions and weaken the electrical attraction - the crystal dissolves.

Learn more about crystal structures on wikipedia.org