of valence electrons, they will react similarly. And in general, this is true. We
mentioned that all of the atoms of elements (except helium) in the extreme right-
hand column of the periodic table (the noble gases) have 8 valence electrons. Do
they have similar reactivities? Yes. These elements (including helium) are all
very unreactive and are said to be part of the noble gas family. A family is a
collection of elements from the same vertical group that have similar chemical
properties. Not surprisingly, all of the members of a particular family have the
same number of valence electrons.
Valence Electrons
Remember that these are
the electrons in an atom’s
outermost shell.There are other important families of elements. All of the atoms of elements in
the extreme left-hand group on the periodic table have 1 valence electron (in an s
subshell). With the exception of hydrogen, these elements—from lithium (Li) to
francium (Fr)—also have much in common. Chemically, all are extremely
reactive. (A piece of potassium, for example, will produce a violent reaction if
placed into water.) Physically, they are shiny, grayish-white metals. However,
they melt more easily than the metals you’re used to seeing, such as iron or
copper. They also tend to have lower densities than the more common metals.
The elements in the first column, from lithium (Li) to francium (Fr), are placed
in the family of alkali metals.
The elements of the group to the right of the alkali metals, from beryllium (Be)
to radium (Ra), constitute another family—the alkaline earth metals. The
alkaline earth metals have 2 valence electrons. They are less reactive than the
alkali metals but more reactive than common metals such as iron and copper.
They look a lot like alkali metals. Because of their highly reactive nature,
elements of the alkali and alkaline earth families are collectively known as the
active metals.
The group of elements alongside the noble gases make up another important
family of elements—the halogens. All of the halogens are very reactive. These
elements are quite physically distinct from one another: Fluorine (F) and
chlorine (Cl) are greenish-yellow, toxic gases; bromine (Br) is a brown liquid at
room temperature; and iodine (I) is a grayish-purple solid. So what makes these
elements a family? All have 7 valence electrons, so they have similar chemical
properties.