Periodic table so on). Each shell consists of one or more subshells (named s, p, d, f and g). As atomic number increases, electrons progressively fill these shells and subshells more or less according to the Madelung rule or energy ordering rule, as shown in the diagram. The electron configuration for neon, for example, is 1s 2s 2p. With an atomic number of ten, neon has two electrons in the first shell, and eight electrons in the second shell; there are two electrons in the s subshell and six in the p subshell. In periodic table terms, the first time an electron
Periodic table atomic number gives a definitive, integer-based sequence for the elements. Moseley predicted, in 1913, that the only elements still missing between aluminium (Z=13) and gold (Z=79) were Z = 43, 61, 72, and 75, all of which were later discovered. The atomic number is the absolute definition of an element, and gives a factual basis for the ordering of the periodic table. The periodic table is used to predict the properties of new synthetic elements before they are produced and studied. In 1871, Mendeleev published his periodic table in a new form, with groups of similar elements arranged in columns