Transition metals such as iron, magnesium or chromium react to form varied colored compounds. Compounds of the same valence have color differences. The transition metals easily form alloys with themselves and other metals. The metals also form salts such as chromium (III) chloride, which is violet in color and dissolves in liquid ammonia to produce a yellow substance that can be separated when the ammonia evaporates.
Colored compounds formed by transition metals include anhydrous copper sulphate (white), potassium permanganate (purple), potassium dichromate (orange), hydrated copper sulphate (light blue) and ammonia copper sulphate (dark blue). The various colors shown by the transition element ions occur because of their light-absorption property in the observable region of the electromagnetic spectrum. The phenomenon causes free electrons to rise from a lower to a higher energy level.
Compounds formed from transition metals show two or more oxidation states. For example, vanadium compounds exhibit oxidation states of between minus 1 and plus 5. The compounds can be paramagnetic or attracted by a magnetic field when they have one or more free electrons in the d sub-orbital. They can be diamagnetic, not pulled by a magnetic field, when no free electrons are present in the d sub-orbital.