Names for sets of chemical elements
There are currently 118 known chemical elements, exhibiting a large number of different physical and chemical properties. Amongst this diversity, scientists have found it useful to use names for various groupings of elements, that illustrate similar properties, or their trends of properties. Many of these groupings are formally recognized by the standards body IUPAC.
The following names are approved by IUPAC:
- Alkali metals – The metals of group 1: Li, Na, K, Rb, Cs, Fr.
- Alkaline earth metals – The metals of group 2: Be, Mg, Ca, Sr, Ba, Ra.
- Pnictogens – The elements of group 15: N, P, As, Sb, Bi.
- Chalcogens – The elements of group 16: O, S, Se, Te, Po. (Lv had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.)
- Halogens – The elements of group 17: F, Cl, Br, I, At.
- Noble gases – The elements of group 18: He, Ne, Ar, Kr, Xe, Rn.
- Lanthanoids – Elements 57–71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu.
- Actinoids – Elements 89–103: Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr.
- Rare earth elements – Sc, Y, and the lanthanoids.
- Transition metals – Elements in groups 3 to 11 or 12.
This English Wikipedia uses the below hybrid system in its periodic table subgroupings. These groupings are called category in this Wikipedia (without any claim to universality):
- Same as the IUPAC system above for alkali metals, alkaline earth metals, noble gases, and transition metals.
- Lanthanoids and actinoids are instead referred to as lanthanides and actinides respectively.
- Rare earth elements, pnictogens, chalcogens, and halogens are not used.
- Additional element groupings used:
- Post-transition metals – The metals of groups 13–16: Al, Ga, In, Tl, Sn, Pb, Bi, Po.
- Metalloids – Elements with properties intermediate between metals and non-metals: B, Si, Ge, As, Sb, Te, At.
- Polyatomic nonmetals – Nonmetals distinguished by polyatomic bonding in their standard states, in either discrete or extended molecular forms: C, P, S and Se.
- Diatomic nonmetals – Nonmetals that exist as diatomic molecules in their standard states: H, N, O, F, Cl, Br, I.
- Superactinides – Hypothetical series of elements 121 to 155, which includes a predicted "g-block" of the periodic table.
Many other names for groups of elements are in common use, and yet others have been used throughout history. Some examples include:
- Precious metal – Variously-defined group of non-radioactive metals of high economical value.
- Coinage metals – Various metals used to mint coins, primarily the group 11 elements of Cu, Ag, and Au.
- Platinum group – Ru, Rh, Pd, Os, Ir, Pt.
- Noble metal – Variously-defined group of metals that are generally resistant to corrosion. Usually includes Ag, Au, and the platinum-group metals.
- Heavy metals – Variously-defined group of metals, on the base of their density, atomic number, or toxicity.
- Native metals – Metals that occur pure in nature, including the noble metals and others such as Sn and Pb.
- 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.
- Transuranium elements – Elements with atomic number greater than 92.
- Transactinide elements – Elements after the actinides (atomic number greater than 103).
- Transplutonium elements – Elements with atomic number greater than 94.
- Minor actinides – Actinides found in nuclear fuel, other than U and Pu: Np, Am, Cm.
- Heavy atom – term used in computational chemistry to refer to any element other than hydrogen and helium.
Any periodic table group can also be used in this sense. Sometimes the group number is used, as in group 14 element, and sometimes the name of the first element in the group is used, as in carbon group or carbon family.