Activity series helps determine what substances will displace others in
reactions. The order in which the elements are listed is usually determined by single-
displacement reactions. The most-active
placed at the top in the series, can replace
each of the elements below it from a compound in a single-displacement reaction. An element farther
down can replace any element below it but not any above it. For example, each halogen will react to
replace any halogen listed below it in the periodic table. Therefore, an
series for
the Group 17 elements lists them in the same order, from top to bottom, as they appear in the periodic
table.
The fact that a chemical
can be written does not necessarily mean that the reaction it
represents will actually take place. Activity series are used to help predict whether certain
reactions will occur. For example, according to the activity series for metals, replaces zinc.
Therefore, we could predict that the following reaction does occur. 2A1 + 3ZnCl2 → 3Zn(s) + 2AlCl3
however, cannot replace sodium. Therefore, we write the following: Co + 2NaCl->
no reaction. It is important to remember that like many other aids used to predict the products of
chemical reactions, activity series are based on experiment.