The Chemistry of Groups

Elements in the same group have the same number of valence electrons, and hence tend to have
very similar chemical properties.

ALKALI METALS

The alkali metals are the elements of Group IA. They possess most of the physical properties
common to metals, yet their densities are lower than those of other metals. The alkali metals have
only one loosely bound electron in their outermost shell, giving them the largest atomic radii of all
the elements in their respective periods. Their metallic properties and high reactivity are
determined by the fact that they have low ionization energies; thus, they easily lose their valence
electron to form univalent cations (cations with a +1 charge). Alkali metals have low
electronegativities and react very readily with nonmetals, especially halogens.

ALKALINE EARTH METALS

The alkaline earth metals are the elements of Group IIA. They also possess many characteristically
metallic properties. Like the alkali metals, these properties are dependent upon the ease with which
they lose electrons. The alkaline earths have two electrons in their outer shell and thus have smaller
atomic radii than the alkali metals. However, the two valence electrons are not held very tightly by
the nucleus, so they can be removed to form divalent cations. Alkaline earths have low
electronegativities and low electron affinities.

HALOGENS

The halogens, Group VIIA (second to last column), are highly reactive nonmetals with seven valence
electrons (one short of the favored octet configuration). Halogens are highly variable in their
physical properties. For instance, the halogens range from gaseous (F 2 and Cl 2 ) to liquid (Br 2 ) to solid
(I 2 ) at room temperature. Their chemical properties are more uniform: The electronegativities of