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Which groups of the periodic table contain the transition metals?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transition metal Modern version of the periodic table of the elements (printable).

Transition metals are defined as the chemical elements that occupy the middle portions of the long periods of the periodic table, specifically spanning Groups 3 through 12.12

These elements are often categorized as the d-block transition metals. While the term "transition" is a convenient designation for these elements, it is used to distinguish the similarity of their atomic structures and properties from the groups located on the left and right sides of the periodic table.31

It is important to note that while the transition metals are generally defined as Groups 3–12, some specific elements within these groups—such as scandium, yttrium, lanthanum, zinc, cadmium, and mercury—are sometimes treated separately in chemical discussions because they may not exhibit all the characteristic properties associated with the main transition series. Additionally, the lanthanoids and actinoids are classified as inner transition series, distinct from the main d-block transition metals.3