Video Transcript
What is the common oxidation number
of alkali metals?
Before we begin to identify the
oxidation number of alkali metals, let us first discuss oxidation numbers. Oxidation numbers show the degree
of oxidation of an atom in isolation or in a compound in terms of counting
electrons. Oxidation numbers tell us how many
electrons an element will gain or lose to form a bond or an ion. When looking at the periodic table,
there are some groups of elements that have trends in terms of oxidation
numbers. For example, noble gases in group
18 are considered chemically inert since their oxidation number is zero because they
do not gain or lose any electrons. As the oxidation number of helium
He and argon Ar is zero, atoms of these elements do not typically form bonds with
atoms of other elements.
Moving across the periodic table to
group 17 are the halogens such as fluorine F and chlorine Cl. These elements usually have
oxidation numbers of negative one since they gain one electron. They can form compounds such as
hydrochloric acid HCl, potassium iodide KI, and sodium bromide NaBr. Oxygen in group 16 has an oxidation
number of negative two since it will gain two electrons and can form compounds such
as Na2O, sodium oxide. Moving further to the left on the
periodic table, we encounter the alkaline Earth metals in group two. This group includes beryllium Be,
magnesium Mg, and calcium Ca. All of these metals have an
oxidation number of positive two since they lose two electrons. They can also form compounds such
as magnesium oxide MgO and calcium fluoride CaF2.
Finally, alkali metals are in group
one which include elements such as lithium Li, sodium Na, and potassium K. Hydrogen H, which is also located
in group one of the periodic table, is not an alkali metal though it has the same
oxidation number as the rest of the elements in group one, which is positive one
because they lose one electron and can form compounds such as sodium chloride NaCl,
also known as table salt, or potassium bromide KBr. After reviewing the trends in the
periodic table about some of the common oxidation numbers, we can conclude that the
common oxidation number for alkali metals is positive one. Positive one is the correct answer
choice.
