Page 190 - Chemistry ICSE Class X

176 ICSE Chemistry – 10
MO(s) + H O(l) o M(OH) (aq)
2
2
oxide of an alkaline alkaline in nature
earth metal
What are the general characteristics of alkaline earth
metals

Some general characteristics of alkaline earth metals are described below:
ƒ Occurrence. Alkaline earth metals are also quite electropositive, but
less electropositive than alkali metals. These elements also do not
occur in the free state. In combined state, alkaline earth metals occur
as carbonates, chlorides, sulphates, etc. Some typical ores of alkaline
earth metals are:
.
Š Magnesium. Magnesite (MgCO ), Dolomite (MgCO CaCO ),
3
3
3
.
.
Epsom salt (MgSO 7H O) and Carnallite (MgCl KCl . 6H O).
2
4
2
2
Š Calcium. Marble (CaCO ), Chalk (CaCO ), Limestone (CaCO ),
3
3
3
.
.
Dolomite (MgCO CaCO ), Gypsum (CaSO 2H O).
3
4
3
2
ƒ Physical state. Alkaline earth metals are greyish-white solids with
metallic lustre.
ƒ Hardness, malleability and ductility. Alkaline earth metals are soft
(but harder than alkali metals), malleable and ductile metals. These
can also be cut with a knife.
ƒ Density. Alkaline earth metals have densities much higher than that
of alkali metals.
ƒ Melting and boiling points. Alkaline earth metals have low, but
much higher melting and boiling points than alkali metals.
ƒ 'NGEVTQPKE EQPſIWTCVKQP Alkaline earth metals have only two
electrons in their outermost shell. Thus, these metals consist of two
valence electrons.
ƒ Chemical reactivity. Alkaline earth metals are also reactive metals.
However, these metals are less reactive than alkali metals. Alkaline
earth metals react with oxygen on heating, and with water (both cold
and hot) they liberate hydrogen.
ƒ Occurrence. Alkaline earth metals do not occur free in nature because
of their higher reactivity.
ƒ Metallic character. Alkaline earth metals are fairly strong metallic
(or electropositive) in nature. However, these are less metallic than
alkali metals. The metallic character of these metals increases down
the group.
ƒ Ionisation energy. The ionisation energies of alkaline earth metals
are fairly low. However, the ionisation energies of alkaline earth
metals are higher than those of alkali metals.
ƒ Electronegativity. Alkaline earth metals have low electronegativity.
Electronegativity of these metals decreases down the group.
ƒ Reducing character. Alkaline earth metals are strong reducing agent.
The reducing character of alkaline earth metals increases steadily in
going down the group.
ƒ Oxidation state. Alkaline earth metals exhibit only +2 oxidation state
in their compounds and in solutions.
ƒ Nature of compounds. Alkaline earth metals (except beryllium) form
electrovalent (or ionic) compounds.