Period (periodic table) eighth period. Period (periodic table) A period in the periodic table is a horizontal row. All elements in a row have the same number of electron shells. Each next element in a period has one more proton and is less metallic than its predecessor. Arranged this way, groups of elements in the same column have similar chemical and physical properties, reflecting the periodic law. For example, the alkali metals lie in the first column (group 1) and share similar properties, such as high reactivity and the tendency to lose one electron to arrive at a noble-gas electronic configuration. As of
Periodic table of topological invariants dimensions can be labeled by the elements of the formula_46-th homotopy group of the symmetric space. These groups are displayed in this table, called the periodic table of topological insulators: There may also exist weak topological invariants (associated to the fact that the suspension of the Brillouin zone is in fact equivalent to a formula_66 sphere wedged with lower-dimensional spheres), which are not included in this table. Furthermore, the table assumes the limit of an infinite number of bands, i.e. involves formula_67 Hamiltonians for formula_68. The table also is periodic in the sense that the group of invariants in formula_46