The elements in a horizontal row of the periodic table .
The periodic table has seven periods. Period 1 contains only two elements, hydrogen and helium. Period 6 (including the lanthanides running from Cerium to Lutetium) contains 32 elements and so is home to more elements than any other period.
Each period begins with an alkali metal and ends with a noble gas, though period 7 is not complete and the putative noble gas with 118 protons has not yet been observed.
Search the Dictionary
