The Activity of
The primary difference between metals is the ease with
which they undergo chemical reactions. The elements toward
the bottom left corner of the periodic table are the metals
that are the most active in the sense of being the
most reactive. Lithium, sodium, and potassium all
react with water, for example. The rate of this reaction
increases as we go down this column, however, because these
elements become more active as they become more metallic.
Based on Activity
The metals are often divided into four classes on the
basis of their activity, as shown in the table below.
Common Metals Divided into Classes on
the Basis of Their Activity
|Class I Metals: The Active
|Li, Na, K, Rb, Cs (Group IA)
|Ca, Sr, Ba (Group IIA)
|Class II Metals: The Less
|Mg, Al, Zn, Mn
|Class III Metals: The
|Cr, Fe, Sn, Pb, Cu
|Class IV Metals: The Coinage
|Ag, Au, Pt, Hg
The most active metals are so reactive that
they readily combine with the O2 and H2O
vapor in the atmosphere and are therefore stored under an
inert liquid, such as mineral oil. These metals are found
exclusively in Groups IA and IIA of the periodic table.
Metals in the second class are slightly less active. They
don't react with water at room temperature, but they react
rapidly with acids.
The third class contains metals such as chromium, iron,
tin, and lead, which react only with strong acids. It also
contains even less active metals such as copper, which only
dissolves when treated with acids that can oxidize the metal.
Metals in the fourth class are so unreactive they are
essentially inert at room temperature. These metals are ideal
for making jewelry or coins because they do not react with
the vast majority of the substances with which they come into
daily contact. As a result, they are often called the
Product of Main Group Metal Reactions
The product of many reactions between main group metals
and other elements can be predicted from the electron
configurations of the elements.
Example: Consider the reaction between sodium and chlorine
to form sodium chloride. It takes more energy to remove an
electron from a sodium atom to form an Na+ ion
than we get back when this electron is added to a chlorine
atom to form a Cl- ion. Once these ions are
formed, however, the force of attraction between these ions
liberates enough energy to make the following reaction
|Na(s) + 1/2
= -411.3 kJ/mol
The net effect of this reaction is to
transfer one electron from a neutral sodium atom to a neutral
chlorine atom to form Na+ and Cl- ions
that have filled-shell configurations.
Potassium and hydrogen have the following electron
When these elements react, an electron has
to be transferred from one element to the other. We can
decide which element should lose an electron by comparing the
first ionization energy for potassium (418.8 kJ/mol) with
that for hydrogen (1312.0 kJ/mol).
Potassium is much more likely to lose
an electron in this reaction, which means that hydrogen gains
an electron to form K+ and H- ions.