The transition metals are a group of metals that are found in the middle of the periodic table. The alkaline earth metals, beginning with beryllium are to the left and the boron group elements are to the right. The term "transition element" was invented for them in 1921.
The atomic numbers of these metals are from 21 to 30, 39-48, 57, 72-80, 89 and 104-112. Many elements like Zn, Cd, Hg, La and Ac have a highly debatable position in the transition series of elements. La and Ac are also classed in the lanthanide series and actinide series respectively.
Transition metals have several general properties. They are harder and less reactive than the alkaline earth metals. They are also harder than the post transition metals. They make colorful chemical compounds with other elements. Most of them have more than one oxidation state. Like other metals, they are electrical conductors.
Some of the transition metals are necessary to keep humans healthy, such as iron, zinc, and chromium. Other elements in the transition metals can be harmful to our body, like cadmium and mercury. Other elements like gold or silver do not harm or help us. There are more transition metals than any other groups in the periodic table.
Only a few of the transition metals are colored; most of them are silver-gray or silver-bluish.