The names of elements with atomic numbers 1–111 appear in the periodic table with respective symbols.
Element 112 and any further newly discovered element(s) may be represented by names derived from their atomic number and corresponding three-letter symbols according to following conventions:
0 = nil
1 = un
2 = bi
3 = tri
4 = quad
5 = pent
6 = hex
7 = sept
8 = oct
9 = enn
Element 112 = Ununbium, symbol Uub.
The element caesium is alternatively spelt as cesium.
In chemical formulae, each element is represented by its symbol appearing in the periodic table. Isotopes are represented by their mass numbers (and atomic numbers) with the same symbol, for example, 188O or 18 O for oxygen-18 isotope. For hydrogen isotopes of mass number two and three, the alternative symbols D and T respectively are also used, but 2H and 3H, are preferred because D and T may disturb the alphabetical ordering of elements in formula. The combination of a muon and an electron is sometimes treated as a light isotope of hydrogen in the name muonium, symbol Mu.
Ions derived from an element A are represented as An+ or An– (not A+n or A–n).
Proton vs. Hydron:
The cation derived from hydrogen is commonly known as proton which is used in many senses, for example, for the isotopically pure 1H+ ion derived from 11H and also for the naturally occurring isotopic composition (containing some 2H+ and 3H+). To avoid confusion, it is now recommended that the undifferentiated isotope mixture be designated by the general name hydron derived from hydrogen. The name proton is reserved for 1H+. The cations 2H+, 3H+ and Mu+ are also known as deuteron, triton and muon, respectively.
Atoms, molecules and allotropic modifications of an element are named by the name of the element with appropriate prefixes where necessary.
When an element does not normally occur in the monoatomic state, the prefix ‘mono’ is used:
Crystalline allotropic modifications of an element may be assigned more sophisticated systematic names with structural parameters. For example, diamond is represented as carbon (cF8) as it has a cubic (c) all-face-centered (F) lattice containing eight (8) atoms of carbon per unit cell. cF is the Pearson symbol of the crystalline variety.
In the periodic classification of elements, certain collective names are IUPAC approved – alkali metals, alkaline earth metals, pnictogens (or pnicogens; N, P, As, …), chalcogens (O, S, …), halogens, noble gases, lanthanoids and actinoids. The last two names are preferred over lanthanides and actinides since the suffix -ide refers to a negative ion.
Roots derived from the names of elements are frequently used in nomenclature. While most of the roots are derived from the common accepted name of the element, some roots are derived from ancient names of the elements. For example, the root ‘az’ for nitrogen derives from the name ‘azote’ (Lavoisier; a = no; zoe = life). Similarly, the Greek name theion provides the root ‘thi’ for sulfur.