Names for sets of chemical elements

There are currently 118 known chemical elements exhibiting many different physical and chemical properties. Amongst this diversity, scientists have found it useful to use names for various sets of elements, that illustrate similar properties, or their trends of properties. Many of these sets are formally recognized by the standards body IUPAC. The following collective names are recommended 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. Transition elements – Elements in groups 3 to 11 or 3 to 12 (the latter equalling the d-block). Pnictogens – The elements of group 15: N, P, As, Sb, Bi. (Mc had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) 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. (Ts had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Noble gases – The elements of group 18: He, Ne, Ar, Kr, Xe, Rn. (Og had not yet been named when the 2005 IUPAC Red Book was published, and its chemical properties are not yet experimentally known.) Lanthanides – Elements 57–71: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. Actinides – Elements 89–103: Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr. Rare-earth metals – Sc, Y, plus the lanthanides. Inner transition elements – f-block elements. Main group elements – Elements in groups 1–2 or 13–18, sometimes excluding hydrogen. Another common classification is by degree of metallic – metalloidal – nonmetallic behaviour and characteristics. There is no general agreement on the name to use for these sets. Very often these categories are marked by a background color in the periodic table.