Editing Period 4 element (section)

{{Short description|Fourth row in the periodic table of chemical elements}}
{{Periodic table (micro)| title=Period 4 in the [[periodic table]] | mark=K,Ca,Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn,Ga,Ge,As,Se,Br,Kr}}
{{Sidebar periodic table|expanded=structure }}
A '''period 4 element''' is one of the [[chemical element]]s in the fourth row (or [[Period (periodic table)|period]]) of the [[periodic table|periodic table of the chemical elements]]. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fourth period contains 18 elements [[#s-block elements|beginning with potassium]] and ending with [[#Krypton|krypton]]&nbsp;– one element for each of the [[group (periodic table)|eighteen groups]]. It sees the first appearance of [[d-block]] (which includes [[transition metal]]s) in the table.