Period 1 element

A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the elements.

Period one is much shorter than any other row in the table, and contains only two elements, hydrogen and helium. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements do not obey the "octet rule".

These are:

عناصر الدورة الأولى Elementos del periodu 1 Elements del període 1 Periode-1-Element Elementos del periodo 1 Elemento de periodo 1 1. periodoko elementu Éléments de la période 1 1주기 원소 Elementi del periodo 1 Elemeent del períut 1 Periode-1-element 第1周期元素 1. perióda 1. периода хемијских елемената Grundämnen i period 1 ธาตุคาบ 1 Chu kỳ nguyên tố 1 1. periyot elementleri 第1周期元素