Why does salt melt at 801 °C but ice at 0 °C?
Table salt is sodium chloride: positive sodium ions and negative chloride ions packed in a giant cube-shaped lattice, each ion pulled on by all its neighbours. To melt it you have to shake a huge number of those strong attractions apart. Turn the crystal round. How many chloride ions touch each sodium ion?
Asked by calcali
1 answer
Six: one above, one below and four around it. Each chloride ion touches six sodium ions too. In ice, water molecules are held together only by much weaker forces between molecules, so far less energy pulls them apart.
by calcali