<P> As of 2016, the periodic table has 118 confirmed elements, from element 1 (hydrogen) to 118 (oganesson). Elements 113, 115, 117 and 118, the most recent discoveries, were officially confirmed by the International Union of Pure and Applied Chemistry (IUPAC) in December 2015 . Their proposed names, nihonium (Nh), moscovium (Mc), tennessine (Ts) and oganesson (Og) respectively, were announced by the IUPAC in June 2016 and made official in November 2016 . </P> <P> The first 94 elements occur naturally; the remaining 24, americium to oganesson (95--118), occur only when synthesized in laboratories . Of the 94 naturally occurring elements, 83 are primordial and 11 occur only in decay chains of primordial elements . No element heavier than einsteinium (element 99) has ever been observed in macroscopic quantities in its pure form, nor has astatine (element 85); francium (element 87) has been only photographed in the form of light emitted from microscopic quantities (300,000 atoms). </P> <P> A group or family is a vertical column in the periodic table . Groups usually have more significant periodic trends than periods and blocks, explained below . Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements within the same group generally have the same electron configurations in their valence shell . Consequently, elements in the same group tend to have a shared chemistry and exhibit a clear trend in properties with increasing atomic number . In some parts of the periodic table, such as the d - block and the f - block, horizontal similarities can be as important as, or more pronounced than, vertical similarities . </P> <P> Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). Previously, they were known by roman numerals . In America, the roman numerals were followed by either an "A" if the group was in the s - or p - block, or a "B" if the group was in the d - block . The roman numerals used correspond to the last digit of today's naming convention (e.g. the group 4 elements were group IVB, and the group 14 elements were group IVA). In Europe, the lettering was similar, except that "A" was used if the group was before group 10, and "B" was used for groups including and after group 10 . In addition, groups 8, 9 and 10 used to be treated as one triple - sized group, known collectively in both notations as group VIII . In 1988, the new IUPAC naming system was put into use, and the old group names were deprecated . </P>

What is the organization of the periodic table