How do the properties of compounds often compare with the properties of the elements that make them

The properties of a compound are nothing like the properties of th elements that combine to make it.

sodium chloride,NaCl, table salt, is a white cubic crystal, stable ionic compound, soluble in water
sodium is a soft metal, very reactive with water and air
chlorine is a yellow green gas that is poisonous and very reactive.

carbon dioxide, CO2, is a clear, colorless gas that puts out fires, plants use but we breath out.
carbon is a black solid, or a diamond
oxygen is a clear colorless gas that is needed for burning and breathing.

Ionic compounds dissociate into component ions dissolved into a solution creating substances called "electrolytes".hope my answer has you : )