The elements are grouped according to their chemical reactivity. Elements with similar properties are listed in radials of the Periodic Spiral and are called groups. Arabic numbers identify the 18 chemical groups, or columns, following the convention adopted by the International Union for Pure and Applied Chemistry (IUPAC) in 1986, but the Periodic Spiral also respects the divisions inherent in Mendeleyev's original Roman alpha-numeric designations. The six angles perpendicular to a hexagon's sides define the arrangement of the groups. Groups 1 and 2 (formerly called groups Ia and IIa in North America and Ia and IIb in Europe) follow the ENE angle, while groups 4 through 7 (formerly called groups IVb through VIIb in North America and IVa and VIIa in Europe) follow the ESE angle; group 3 (formerly called group IIIb in North America and IIIa in Europe), including the lanthanon and actinon series, inhabit the space between. Groups 8, 9, and 10 (formerly called group VIII) and 11 (formerly called group Ib in North America and Ia in Europe) occupy the south angle; group 12 (formerly called group IIb in North America and IIa in Europe), the WSW angle; groups 1317 (formerly called group IIIa through VIIa in North America and IIIb through VIIb in Europe), the WNW angle; and group 18 (formerly called group 0), the north angle. Elements on the right side of the Periodic Spiral tend to lose their valence electrons in chemical reactions; the atoms of the elements toward the left side of the Periodic Spiral tend to undergo reactions such that they gain (or share) enough electrons to complete their valence shell. Click on any of the headings in the box above for more detail.