What is Period 4 element?
A '''period 4 element''' is an [[Chemical element|element]] in the fourth [[period (periodic table)|period]] (row) of the [[periodic table]]. It begins at [[potassium]] and ends at [[krypton]]. Period 4 has 18 elements. Period 4 elements have [[electrons]] in the first four [[electron shell]]s. All period 4 elements have one or more electrons in the fourth electron shell ([[valence electrons]]). When atomic number increases by one, another electron is added. Two electrons join the 4s [[atomic orbital|orbital]], ten electrons join the 3d orbital, and six electrons join the 4p orbitals. {{Periodic tables footer}} [[Category:Periodic table]] {{chem-stub}}