CBSE, NCERT, CLASS 11, CHEMISTRY, P BLOCK, GROUP 13, BORON FAMILY

1. Group 13 elements :
The Boron Family
-Puneeta Malhotra

2. Group 13
• Group 13 or the Boron family has Boron (B) ,
Aluminium (Al) , Gallium (Ga) , Indium (In) ,
Thallium (Tl) .
• Al is the most abundant metal on Earth .
• Al is third most abundant element in the Earth’s
crust .

3. Electronic Configuration
• General electronic configuration ns2np1
• Stable Oxidation state +3 decreases as we
move down the group due to inert pair effect.

4. What is Inert Pair Effect ?
• Reluctance of ns2
electrons to take
part in bonding due
to the poor shielding
effect of intervening
d and f orbitals on
moving down the
group is known as
Inert Pair Effect .

5. ATOMIC SIZE

6. Atomic Radii
• Atomic Radii (pm)
• B 85
• Al 143
• Ga 135
• In 167
• Tl 170
• On moving down the group atomic radius
is expected to increase.
• However, Atomic radius of Ga is less than that of Al.
due to the poor screening effect of intervening
d orbitals

7. Ionization Enthalpy
• The ionization enthalpy values do not decrease
smoothly down the group.
• Variation can be explained on the basis of poor
screening effect of d and f electrons.
• IE1<IE2<IE3
• Sum of IE1+IE2+IE3 is very high

8. Electronegativity
• B 2.0
• Al 1.5
• Ga 1.6
• In 1.7
• Tl 1.8
• Down the group, electro negativity first
decreases from B to Al and then
increases marginally because of the differences
in atomic size of the elements.

9. Physical Properties
• Boron is hard black coloured high melting
(Due to very strong crystalline lattice) non
metallic solid .
• Others are soft metals with low melting
point and high electrical conductivity.
• Density of the elements increases down
the group from boron to thallium.
• Ga it a useful material for measuring high
temperatures as it has low mp and very high bp.

10. Oxidation State And Trends In
Chemical Reactivity
• Except B all other are metals
• Boron due to small size and high IE1+IE2+IE3
does not form B3+ , forms covalent compounds.
• Aluminum (Al) forms +3 cations.
• Gallium (Ga), indium (In), and thallium (Tl) all
form +3cations, but also +1 cations .
• The relative stability of +1 oxidation state
progressively increases as we move down in the
group due to inert pair effect
Al<Ga<In<Tl

11. • BF3 AlCl3 etc behave as LEWIS ACIDS
(electron deficient molecules have
tendency to accept a pair of electrons to
achieve stable electronic configuration)
• The tendency to behave as Lewis acid decreases
with the increase in the size down the group.
• AlCl3 achieves stability by forming a dimer

12. Reactivity Towards Air
• Boron is unreactive in crystalline form.
• Aluminium forms a very thin oxide layer on the
surface which protects the metal from further
attack.
• Amorphous boron and aluminium metal on
heating in airform B2O3 and Al2O3 respectively.

13. • Basic nature of these oxides increases down the
group.
• Boron trioxide is acidic ,Aluminium and gallium
oxides are amphoteric and those of indium and
thallium are basic in their properties.

14. Reactivity Towards Nitrogen
• Only B and Al forms nitrides at high
temperature

15. Reactivity Towards Acids and Alkalies
• B does not react with acids and alkalies even at
moderate temperature.
• Al shows amphoteric character.
• Aluminium dissolves in dilute acids and
alkalies and liberates hydrogen.
• In concentrated HNO3 Al becomes passive by
forming a protective oxide layer on the surface.

16. • Aluminium dissolves in dilute acids and
alkalies and liberates hydrogen.
• In concentrated HNO3 Al becomes passive by
forming a protective oxide layer on the surface.

17. Reactivity Towards Hydrogen
• These elements react with
halogens to form tri halides(except TlI3).
• 2E(s)+ 3 X2(g)→ 2EX3(s)
(X = F, Cl, Br, I)

18. Reactivity towards halogens
• These elements react with halogens to form
trihalides (except Tl I3).
• 2E(s) + 3 X2 (g) → 2EX3 (s) (X = F, Cl, Br, I)

19. ANOMALOUS PROPERTIES OF BORON
• Due to small size and high electronegativity,
form covalent compounds
• due to the absence of d orbitals that the
maximum covalence of B is 4.

21. Borax Na2B4O7⋅10H2O
• tetranuclear units [B4O5 (OH)4]2-.
Correct formula; therefore, is
Na2[B4O5 (OH)4].8H2O.
• Borax dissolves in water to give an alkaline
• solution.
• Na2B4O7 + 7H2O → 2NaOH + 4H3BO3
(Orthoboric acid)

22. borax bead test
• Na2B4O7.10H2O ( heat)→Na2B4O7 Sodium
metaborate
• Na2B4O7 (heat) →2NaBO2 + B2O3
Boric anhydride
• The metaborates of many transition metals
have characteristic colours and, therefore,
borax bead test can be used to identify them
in the laboratory.

23. Orthoboric acid H3BO3
• Boric acid is a weak monobasic acid.
• It is not a protonic acid but acts as a Lewis acid
by accepting electrons from a hydroxyl ion:
• B(OH)3 + 2HOH → [
• On heating, orthoboric acid above 370K forms
metaboric acid, HBO2 which on further heating
yields boric oxide, B2O3.

25. Diborane, B2H6

26. • Each B atom uses sp3 hybrids for bonding. Out
of the four sp3 hybrids on each B atom, one is
without an electron shown in broken lines. The
terminal B-H bonds are normal 2-centre-2-
electron bonds but the two bridge bonds are 3-
centre-2-electron bonds. The 3-centre-2-
electron bridge bonds are also referred to as
banana bonds.

27. Thank You