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GROUP 13 ELEMENTS
Ionisation Energy Concept Ladder
The first ionisation energies (IE1) of group
13 elements (Boron family) are lower than the
Stability of +3 oxidation
corresponding elements of group 2 (AEM). This
state : B > Al > Ga > In > Tl
is due to the electronic configuration of group 13
Stability of +1 oxidation
elements ns2 np1 and the electron thus has to be
state : Ga < In < Tl
removed from the p-orbital which is much easier
Ionisation energy : B > Al <
than removing an s-electron of AEM elements,
Ga > In < Tl
which is more strongly atracted by the nucleus.
Boron has higher ionisation energy than its group
members because its is considerable smaller.
The ionization energy is so high that boron is
always covalent.
Oxidation State
Due to ns2, np1 configuration of the valence
Rack your Brain
shell, group 13 elements are expected to be
trivalent but there is increase in ability to form
Why boron has high melting and
univalent compounds on moving down the group.
boiling point?
The oxidation state of B and Al is +3 while Ga, In,
Tl show oxidation state of both +3 and +1. It is
due to Inert Pair Effect.
Metallic Character/Reducing Power
The order is : B < Al > Ga > In > Tl
The increase in metallic character from
Boron to Aluminium due to increase in atomic
size but Ga, In, Tl do not follow the trend. They
follow immediately after a row of ten transition
elements and thus have 10 d-electrons which Previous Year’s Questions
are less efficient for shielding the nuclear charge
than s,p electrons. Thus outer most electrons The correct order of atomic radii
p-Block Elements (Part-1)
being more firmly held by the nucleus are more in group 13 elements is
difficult to remove than expected. This leads to [NEET 2018]
decrease in size as well as decreases in metallic (1) B < Al < In < Ga < Tl
character than would be expected. This (2) B < Al < Ga < In < Tl
phenonmenon is know as d-block Contraction. (3) B < Ga < Al < Tl < In
(4) B < Ga < Al < In < Tl
1.
, Similarly for Tl which is followed immediately
after 14-f-block elements, there is much change Concept Ladder
in the size and metallic character of it. It is due
to the Lanthanide Contraction which is due to
The electropositive or
the f-block elements. Note that in general the
metallic character of group
size increases down the group but is less than
13 elements increases
as expected.
from B to Tl. B being a non
metal and thus forms an
Acidic Character
acidic hydroxide. Al forms
From B to Tl acidic character decreases and basic
amphoteric hydroxide and
character increases because ionization energy
Tl, the most metallic from
increases. Thus we find that B(OH)3 , and B2O3 are
basic hydroxides.
acidic ; Al(OH)3 and Al2O3 are amphoteric; Ga(OH)3
and Ga2O3 are amphoteric; and In(OH)3 , TI(OH)3
are basic.
Rack your Brain
Boron & Its Compound Which elements of group 13 will
Physical Properties and Occurrence form most ionic and covalent
Boron occurs in two allotropic form : compounds respectively?
(a) Crystalline – It is chemically inert, very hard
and black in color.
(b) Amorphous – It is chemically active, a
non–conductor, difficiult to fuse and brown in
color.
All allotropic forms contain icosahedral
unit with atoms at all 12 corners. The important
minerals of boron are :
p-Block Elements (Part-1)
, Extraction of Boron : It includes 2 steps :
1. Preparation of Boric anhydride (B2O3) : Rack your Brain
[Method–I] If Borax can be formulated
as Na2[B4O5(OH)4].8H2O then
Na 2B4O7
2 HCl
2 NaCl
H2B4O7 how would you formulate
powdered Borax
conc.
Colemanite?
H2B4O7
5 H2O
4 H3BO3
sparingly soluble orthoboric acid
2 H3BO3
B2O3
H2O
[Method–II]
Ca 2B6O11 2 Na 2CO3
2 CaCO3 Na 2B4O7 2 NaBO2
powdered
fuses
colemanite
The fused mass is extracted with. CaCO3
remains filtrate and insoluble containing sodium
metaborate. By obtained borax crystals, borax is Concept Ladder
put to crystallisation. The remaining solution is
treated with CO2.
On a large scale, boron
4 NaBO2 CO2
Na 2B4O7 Na 2CO3 is extracted from its
Borax
minerals, borax Na2B4O7
and colemanite Ca2B6O11.
Then Method I is followed. The latter is first converted
to borax by boiling with
a solution of sodium
[Method III] carbonate in the requisite
Suspension of colemanite mineral in H2O is proportion and then the
formed and SO2 gas is passed to obtain crystal of same method is followed.
boric acid on cooling.
p-Block Elements (Part-1)
Then, 2 H BO
B2O3
3 H2O
3 3
crystals
4.
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