The outer transition metals have high melting and boiling points due to the strong bonding between the atoms of the element. The melting point of all these metals is not lower than 1,000 degrees centigrade, except zinc, which melts at 419.5 degrees centigrade. These d-block elements are therefore also put to uses in which a high strength at a high temperature is required. Alloys of these metals are commonly used in engines, heat exchangers and turbines.
The outer transition metals are known to form colored compounds after reacting with other elements. This is because these elements absorb light of specific wavelengths, resulting in a specific color of the compound. Outer transition metals tend to form more colored compounds than other elements, either in solid form or in dissolved form. The colored compounds often have a complex structure and are therefore called complexes. Usually, titanium chloride is purple, vanadium chloride is green, chromium sulfate is dark green, potassium manganate is purple, and iron chloride is yellow-orange-brown in color. Cobalt sulfate is pinkish, nickel chloride is green, and copper sulfate is deep-blue in color.
Many of the outer transition metals have found extensive use as catalysts in industrial chemical processes and in the antipollution catalytic converters in automobile exhaust systems. Iron is used in the Haber synthesis of ammonia, and nickel is the catalyst for hydrogenation (addition of hydrogen) in the margarine industry. Along with the outer transition metals, the compounds of these metals also act as catalysts.
The outer transition metals have high densities due to the strong attractive force between the atoms, which tightly holds the atomic molecules. For example, iron has a density almost 8 times that of sodium, which is an alkali metal.