Page 150 - Chemistry ICSE Class IX

138 ICSE Chemistry – 9
Š Sodium occurs as rock salt, as common salt (NaCl), in sea and lake
water, as chile saltpetre (NaNO ).
3
.
Š Potassium occurs as Carnallite (KCl . MgCl 6H O), Sylvine (KCl).
2
2
ƒ Physical state. All alkali metals are silvery white solids with metallic
lustre. These metals are quite light.
ƒ Hardness, malleability and ductility. Alkali metals are soft, highly
malleable and ductile. These can be cut easily with a knife. Lithium
is the hardest of all the alkali metals.
ƒ Melting and boiling points. Alkali metals have low melting and
boiling points. The melting and boiling points decrease as we go
down the group.
ƒ 'NGEVTQPKE EQPſIWTCVKQP Alkali metals have only one electron in
their outermost shell. Thus, each alkali metal has only one valence
electron.
ƒ Chemical reactivity. Alkali metals are very reactive. The reactivity
of alkali metals increases down the group. These elements react with
oxygen (in air) and moisture rapidly even at room temperature.
Freshly cut alkali metals are shiny but soon get tarnished (or become
dull) when exposed to the air due to the formation of oxide layer.
ƒ Storage. Alkali metals are stored (or kept) under kerosene or RCTCHſP
oil because they react rapidly with oxygen and moisture (present in
the air).
ƒ Metallic character. All alkali metals are strongly metallic (or highly
electropositive). Metallic (or electropositive) character increases as
we go down the group. Cesium is the most metallic element.

Alkaline Earth Metals (Group 2)

Elements of Group 2 (or group IIA) are called alkaline earth metals.
Group 2 (or group IIA) contains, Beryllium (Be), Magnesium (Mg),
Calcium (Ca), Strontium (Sr), Barium (Ba) and Radium (Ra). These elements
are collectively called alkaline earth metals.

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).
4
2
.
Š Calcium. Marble (CaCO ), Dolomite (MgCO CaCO ), Gypsum
3
3
3
.
(CaSO 2H O).
2
4
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.