The transition metals are the largest group of elements on the periodic table. They got their name because English chemist Charles Bury described a transition series of elements in 1921. Bury examined the transition from an inner electron layer with 8 electrons to a layer with 18 electrons and from a layer of 18 electrons to one with 32. Today, most people think of these elements as transitioning from one side of the periodic table to the other. Moving from left to right across the periodic table, an electron is added to the d orbital of each atom, transitioning from group 2 to group 13.
Here’s a look at the different ways of defining the transition metals, a list of which elements are included, and a summary of their common properties.
Transition Metal Definition
The most common definition of a transition metal is the one accepted by the IUPAC. A transition metal is an element with a partially-filled d subshell or the capacity to produce cations with an incomplete d subshell.
Other people consider the transition metals to include any d-block element on the periodic table. Under this definition, groups 3 to 12 are the transition metals and the f-block lanthanide and actinide series are called the “inner transition metals.”
List of Transition Metal Elements
Using the IUPAC definition, there are 40 transition metals. They are:
- Atomic numbers 21 (scandium) to 30 (zinc)
- Atomic numbers 39 (yttrium) to 48 (cadmium)
- Atomic numbers 71 (lutetium) to 80 (mercury)
- Atomic numbers 103 (lawrencium) to 112 (copernicium)
The full list is:
Technically, the elements zinc, cadmium, and mercury (group 12) should be considered post-transition rather than transition metals because they have a full d10 configuration and normally produce ions that retain this configuration. Experimental evidence of mercury behaving as a transition metal was obtained in 2007. Copernicium should probably be excluded on the same basis, although its oxidation properties have not been verified experimentally. However, most people include these elements in the transition metal list.
Some people exclude lutetium and lawrencium from the list. But, lutetium and lawrencium are technically group 3 elements that fit in the “space” in the periodic table. There are also scientists and educators who include the full lanthanide and actinide series as transition metals.
Transition Metal Properties
The transition metals display several characteristic properties:
- They often form colored compounds. The colors are due to d-d electronic transitions.
- They readily form complexes.
- They display multiple positive oxidation states. This is because of the low energy gap between states.
- They are good catalysts.
- They are silver metals at room temperature. The exceptions are copper and gold.
- They are solids at room temperature. The exception is mercury.
- They are paramagnetic (attracted to a magnetic field). Generally, paramagnetism results from unpaired d-electrons. Three important elements regarding magnetism are iron, cobalt, and nickel. All three elements produce a magnetic field.
- They exhibit metallic luster.
- They have low ionization energies.
- They are hard.
- The metals have high melting and boiling points (except mercury).
- They are good electrical and thermal conductors.
- They form alloys.
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
- IUPAC (1997). Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).
- Jensen, William B. (2003). “The Place of Zinc, Cadmium, and Mercury in the Periodic Table”. Journal of Chemical Education. 80 (8): 952–961. doi:10.1021/ed080p952