science question! please help?

Question

what causes a solid object to dissolve

Answer 1

Lots of interactions occur, and it depends on the chemical structures involved, but let's take simple case of salt in water.

Salt is actually sodium chloride, or NaCl. If you examine salt closely, you will see it is made of small crystals. If you look at it really closely, like under a microscope, you will see that the crystals have a lattice structure. In this structure, positive sodium ions and negative chloride ions attract each other strongly.

Water molecules in contact with a crystal orient themselves to neutralize the attractive forces between the ions in the crystal structure. The positive end of the water dipole is attracted to the chloride ions, and the negative end of the water dipole to the sodium ions. The polar water molecules thus weaken the attraction between sodium and chloride ions. The weakened attraction permits the ions to move apart, making room for more water dipoles. Each liberated ion is then hydrated by more water molecules, preventing them from recombining and recrystalizing.

The hydrated ions slowly diffuse away from the crystal to become dissolved in solution.