why do the sugar crystals reform when the water is taken away?

Question

..sugar dissolves in water; and sugar crystals reform if you evaporate the water.

Answer 1

Some compounds have a specific geometrical shape which allows crystal structure to happen. Sucrose is one of these.

When you dissolve the sugar crystals in water, the water forms hydrogen bonds with parts of the sucrose molecules (specifically the -OH's and =O's) and this allows the molecules to be pulled from the crystals and go into solution.

When the water is allowed to evaporate, the solution becomes saturated and can no longer hold as much sucrose. These sugar molecules that come out of the solution tend to group back into the pattern which contains the least amount of energy. This is the crystal form.

For solid which do not have a crystalline form you just end up with a solid powder.

Answer 2

The sugar crystals reform because they are only mixed (not chemically combined) with the water. By removing the water trhough evaporation, the sugar is left behind and goes back to its original form, crystals.