s block elements

,↓ Group I elements are called alkali metals because
they form
hydroxides with


water which are
strongly alkaline
.




2 Group 2 alkaline metal
elements with exception of Beryllium called -




3 .


↳i Lower abundance



Na Guigner abundance




Rb
lower abundane a




Fr > Radioactive ,
longest-lived isotope Fr-tyz = 21 minutes




4 -
Be-rare


Mg-h Jabundance in
a so




SV Y
lower abundane
a




Ra-10 % in
igneous rocks (rarest)


.
5 Li Be

MG An
↳
Diagonal relationship



Diagonal relationship is due Similarity
to in ionicsizes Charge/radius vario
·
,




.
6 Alkali metal lose one electron readily so they never Found in free state in


nature




.
7 Alkali metal has the largest atomic size in the period

, Lit > Rb+> cst
+
.
8 hydration enthalpy : > Nat K




lithium salts mostly . (Licl 210)
so
hydrated
·
are .




9 .




Physical properties of alkali metal :




· all are
silvery metal ,
soft and
light
·
low density due to large size


density Li-
·
: > Cs


·
K is lighter than wa

·
weak mettalic bond due to one valence bond

·
Li-Crimson red

Na-yellow

K- Violet

Rb -
Red violet

Cs -

Blue

·
This excitation of Cs and K is used in electrode

of Photoelectic cell




10 .

Chemical properties of alkali metal :


metal
·
The alkali tarnish in air due to oxide formation ,
A

in with moisture from
for they react to
hydroxide
Liz also Theyreachgrously in
presence of oxygen to form oxide
·
·




formed in Li-> monoxide 41 + 02-2Li0
>
air directly Na > Peroxide 2Na-oz Na O
-
-



,




hY
combining with
superoxidea
M + 02
>
MO
Nitrogen
-

-




·
Because of higher reactivity they kept
are
normally
under Kerosene oil .