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 (crystal structure) Periodic table (crystal structure) For elements that are solid at standard temperature and pressure the table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. In all other cases the structure given is for the element at its melting point. Data is presented only for the first 114 elements as well as the 118th (hydrogen through flerovium and oganesson), and predictions are given for elements that have never been produced in bulk (astatine, francium, and elements 100–114 and 118). Among the undiscovered elements, predictions are only available for ununennium and unbinilium (eka-francium and eka-radium), which are