Specifically, they are grouped within the same vertical column, which is called a group or family.
For example:
* Group 1 (alkali metals): Lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr) are all soft, highly reactive metals that readily lose one electron to form a +1 ion.
* Group 17 (halogens): Fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At) are all nonmetals that readily gain one electron to form a -1 ion. They are all highly reactive and form diatomic molecules.
This similarity in properties is due to the fact that elements in the same group have the same number of valence electrons, which are the electrons in the outermost shell of an atom. These valence electrons are responsible for an element's chemical behavior.
