Page 188 - Chemistry ICSE Class X

174 ICSE Chemistry – 10

How is the metallic and nonmetallic character of an
element related to its electronic configuration
The chemical properties of any element depend upon its electronic
EQPſIWTCVKQP 5Q YJGVJGT CP GNGOGPV DGJCXGU NKMG C OGVCN QT PQPOGVCN
FGRGPFU WRQP KVU GNGEVTQPKE EQPſIWTCVKQP 6JWU C OGVCN CPF C PQPOGVCN
FKHHGT KP VJGKT GNGEVTQPKE EQPſIWTCVKQPU
ƒ Metals generally have 1 to 3 electrons in the outermost shell (or
,LJĚƌŽŐĞŶ ĂŶĚ ŚĞůŝƵŵ ĂƌĞ ƚŚĞ ŽŶůLJ valence shell) of their atoms.
ŶŽŶŵĞƚĂůƐ ǁŚŝĐŚ ĐŽŶƚĂŝŶ ŽŶĞ ĂŶĚ
ƚǁŽ ĞůĞĐƚƌŽŶƐ ƌĞƐƉĞĐƟǀĞůLJ ŝŶ ƚŚĞŝƌ ƒ Nonmetals usually have 4 to 8 electrons in the outermost shell (or
ŽƵƚĞƌŵŽƐƚ ƐŚĞůůƐ͘ valence shell) of their atoms.
Hydrogen and helium, however, do not follow this rule.
Hydrogen (H) and helium (He) are nonmetals. Hydrogen has only
one electron in its outermost (or valence) shell, i.e. hydrogen has only one
electron in its K-shell. Helium (He) has two electrons in its outermost (or
valence) shell, i.e., helium has two electrons in its K-shell.

Alkali Metals

Elements of Group 1 (or Group IA) are called alkali metals. Group 1 (or
'ƌŽƵƉ ϭ Group IA) contains Lithium (Li), Sodium (Na), Potassium (K), Rubidium
Li (Rb), Cesium (Cs) and Francium (Fr). These elements are collectively
called alkali metals because these metals react with water to form their
Na
hydroxides which are strong alkalis.
K
2M(s) + 2H O(l) o 2MOH(aq) + H (g)
Zď 2 2
(Li,Na,K,Rb,Cs) water alkali metal hydroxide hydrogen
Cs alkali metal (strong alkali)
&ƌ
What are the general characteristics of alkali metals
Alkali metals occupy Group 1
(or Group IA) of the periodic table. Some common/general characteristics of alkali metals are described below:
ƒ Occurrence. All alkali metals are highly reactive and therefore, do not
occur in free metallic state. These metals occur as their compounds.
For example,
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.