Page 6 - 9-CHEM-8-newflip

8. Chemical Reactivity eLearn.Punjab
Animation 8.7:cesium
8.1.1 Electropositive Character Source & Credit: amoebamike

Metals have the tendency to lose their valence
electrons. This property of a metal is termed
as electropositivity or metallic character. The
more easily a metal loses its electrons, the more
electropositive it is. The number of electrons lost by
an atom of a metal is called its valency. For example,
sodium atom can lose 1 electron to form a positive
ion.

So the valency of sodium metal is 1.
Similarly zinc metal can lose 2 electrons from its
valence shell. Therefore, its valency is 2.

Trends of electropositivity

Electropositive character increases down the group because size of atoms increases. For example,
lithium metal is less electropositive than sodium which is in turn less electropositive than potassium.
Electropositive character decreases across the period from left to right in the periodic table because
atomic sizes decrease due to increase of nuclear charge. It means elements at the start of a period
are more metallic. This character decreases as we move from left to right along the period

Electropositivity and ionization energy

Electropositive character depends upon the ionization energy which in turn depends upon size and
nuclear charge of the atom. Small sized atoms with high nuclear charge have high ionization energy
value. In this way, atoms having high ionization energy are less electropositive or metallic. That is
the reason alkali metals have the largest size and the lowest ionization energy in their respective
periods.

6