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Metals and Non-Metals - Part IV |
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3. Reactivity series of metals : We have seen that some metals are more reactive than the others. In the chapter on Classification of Elements we have seen that the reactivity of elements decreases as we go from the left to right in the periodic table. Alkali metals from group 1 A such as Na, K, Cs are most reactive. Alkaline earth metals from group 2 A such as Mg, Ca are reactive but are less reactive than the alkali metals. In
the alkali group, as we go down the group we have elements Lithium (Li),
Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs) and Francium (Fr).
They have all only one electron in their outermost shells. All the elements
show metallic properties and have valence +1.
They give up electron easily. Reactivity or the ease with which these
elements give off their electrons increases with the size of the atoms. The
size of the atom increases from Li to Fr. The outermost electron is less
loosely bound in Fr than in Li, as in Fr the distance between the last
electron and the positive nucleus is large; this makes the attractive force
binding or holding the electron to be less. Thus K will give up electron
more easily than Na. This makes K more reactive than Na. The
alkaline earth group, as we go down the group we have elements Beryllium
(Be), Magnesium(Mg), Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium
(Ra). They have two electrons in their last shell and their valence is +2 as
they give up two electrons to form compounds. The elements in group II A are
not as metallic as the alkali metals. Reactivity or the ease with which
these elements give off their electrons increases with the size of the
atoms. The size of the atom increases from Be to Ra. The outermost electron
is less loosely bound in Ra than in Be, as in Ra the distance between the
last electron and the positive nucleus is large; this makes the attractive
force binding or holding the electron to be less. Thus Ca will give up
electron more easily than Mg. This makes Ca more reactive than Mg. The
transition group elements such as Zn, Fe, Sn. Pb. Cu are also metallic and
reactive. But the ease with which they loose electrons is less than that we see
in alkali or alkaline earth metals. The
table below shows the reactivity series of metals. Hydrogen has been
included in the table, although it is a non-metal. H is a special case
because although it is a non-metal, it gives off an electron while forming
bonds. Metals
which are more reactive than hydrogen are K, Na, Ca, Mg, Al, Zn, Fe, Sn and
Pb. These metals can displace H from water or dilute acids and liberate
hydrogen gas. Metals
which are less reactive than hydrogen are Cu, Hg, Ag. These metals do
not replace H in a reaction with water or dilute acids.
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