There are currently 118 known chemical elements, exhibiting a large number of different physical and chemical properties. However, amongst this diversity, scientists have found it useful to label several groupings of elements, to illustrate similar properties, or trends of properties. Many of these groupings are formally recognised by the standards body IUPAC.^[1]

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.
• 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 12.

Wikipedia uses the below hybrid system in its periodic table- and chemical element-related articles:

• Same as the IUPAC system above for Alkali metals, Alkaline earth metals, Halogens, Noble gases, Lanthanoids, Actinoids, and Transition metals.
• Rare earth elements, Pnictogens and Chalcogens are not used.
• Leftover elements are grouped as:
  • Post-transition metals – Metals with complete d-subshells to the right of the transition elements: Al, Ga, In, Sn, Tl, Pb, Bi, Po.
  • Metalloids – Elements with properties intermediate between metals and metalloids: B, Si, Ge, As, Sb, Te.
  • 'Other non-metals' – Non-metals that are not otherwise categorized: – H, C, N, O, P, S, Se.

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.
• 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.
• Poor metal – Sometimes used to refer to the metals of the p block: Al, Ga, In, Sn, Tl, Pb, Bi, Po. This group is very similar to Post-transition metals.
• 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 that U and Pu: Np, Am, Cm.
• Superactinides – Hypothetical series of elements 121 to 155, which includes a predicted "g-block" of the periodic table.
• 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.

References [edit]

1. ^ International Union of Pure and Applied Chemistry (2005). Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005). Cambridge (UK): RSC–IUPAC. ISBN 0-85404-438-8. Electronic version. Retrieved 10 June 2012.

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