Period 4 of the Periodic Table
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Period 4 of the periodic table (also called the fourth period) is one of the horizontal rows of the periodic table of chemical elements. Elements in this period have four electron shells (orbitals in which electrons orbit the nucleus).
The period begins with potassium (K) and ends with krypton (Kr). It is the first period in which transition metals appear, arising from the filling of the inner 3d orbital.
Elements in the period
The period contains potassium and calcium (alkaline earth metals), followed by the transition metals including scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. After these come gallium, germanium, arsenic, selenium, bromine, and the noble gas krypton.
Electron configuration
Elements in this period fill the 4s, 3d, and 4p orbitals. The 4s orbital fills first, then the 3d, and finally the 4p. The variable filling of the 3d orbital is responsible for transition metals having multiple oxidation states and various colors in their compounds.
Significance
Many elements in this period play important roles in life and industry. Iron and copper are essential for tools and electrical wiring. Potassium and calcium are among the elements living organisms require, while iron, zinc, manganese, cobalt, and copper function in small quantities as components of enzymes in the body.