There are currently 118 known
chemical elements with a wide range of physical and chemical properties. Amongst this diversity, scientists have found it useful to apply names for various sets of elements that have similar properties, to varying degrees. Many of these sets are formally recognized by the standards body
IUPAC.[1]
IUPAC
The following collective names are recommended or noted by IUPAC:
Elements in groups 1–2 or 13–18, excluding hydrogen
* Transition elements are sometimes referred to as transition metals
† Although the heavier elements of groups 15 (Mc), 16 (Lv), 17 (Ts) and 18 (Og) have been notionally assigned to the indicated groups their chemical properties have not yet been experimentally confirmed.
‡ Lanthanoids and actinoids are sometimes referred to as lanthanides and actinides respectively
Metallicity-based
Another common classification is by degree of metallic or nonmetallic behaviour and characteristics. Elements in the vicinity of where the metals and nonmetals meet are sometime classified as
metalloids or an equivalent term. These two to three classes are commonly marked by differing background colors in the periodic table.
Common and historical
Many other names for sets of elements are in common use; others have been used throughout history. These sets usually do not aim to cover the whole periodic table (as for example period does), and often overlap or have boundaries that differ between authors. Some examples:
Metalloids – Variously-defined group of elements with properties intermediate between metals and nonmetals.
In alphabetic order:
Coinage metals – Various metals used to mint coins, primarily the group 11 elements Cu, Ag, and Au.
Earth metal – Old historic term, usually referred to the metals of groups 3 and 13, although sometimes others such as beryllium and chromium are included as well.
Heavy metals – Variously-defined group of metals, on the base of their density, atomic number, or toxicity.
Post-transition metals – The metals coming after the transition metals. Many other names have been used for this set, and its borders are not agreed on.
Precious metals – Variously-defined group of non-radioactive metals of high economical value.
Superactinides – Hypothetical series of elements 121 to 157, which includes a predicted "g-block" of the periodic table.