1
BORON FAMILY(GROUP 13)
PART V.

GROUP 13 ELEMENTS-THE BORON FAMILY
ELEMENT SYMBOL ELECTR. CONF.
Boron B [He]2s22p1
Aluminium Al [Ne]3s23p1
Gallium Ga Ar]3d104s2 4p1
Indium In [Kr]4d105s2 5p1
Thallium
2
Tl [Xe]4f145d106s2 6p1

3
INTRODUCTION
➢Boron is the only group 13 element that is a
non-metal.
▪ The remaining members of this group are
fairly reactive metals, and are called p-block
elements.
▪ Aluminium, Al, is the third most abundant
element in the Earth's crust
▪ All elements show a stable oxidation state of
+3, except for thallium. 3

4
▪ The small sizes of the ions, their high charge and
large values for their sum of the 1st ionization energy
suggest that the elements are largely covalent.
▪ Boron is always covalent and many simple
compounds like AlCl3 and GaCl3 are covalent when
anhydrous.
▪ However, in solution, the large amount of hydration
energy evolved offsets the high I.E and
hence all ions exists in hydrated states.

5
▪ Unlike the s-block elements, some of the elements of
this group display lower valency.
▪ There is an increase in tendency to form univalent
compounds as you go down the group, and univalent
thallium compounds are the most stable.
▪ This monovalency is occurs because s-electrons in the
outer shell remaining paired, and therefore not
participating in bond formation……because
the energy to unpair them is too great.

6
▪ This tendency occurs among heavy
elements in the p-block and is called the
INERT PAIR EFFECT.
▪ Inert Pair Effect is the resistance or
reluctance of s-electrons to get unpaired, or
take part in covalent bonding.
▪ It is only p orbital electrons, which are
involved in bond formation.
6

7
▪ Group 13 metals have silver luster.
▪ Erratic variation in M.P is observed down the group.
B(2300 ºC), Al(660.4 ºC), Ga(29.78 ºC), In(152.6 ºC) and Tl(303 ºC)
•
• Low M.P of Ga is reflected in the unusual structure of
the metal, which contains Ga2.
The general trend down Group from non-metallic to
metallic character.
– Boron has a covalent network structure.
– Other elements are more ionic and metallic in
character.

8
– Aluminium is on the borderline between ionic and
covalent character in its compounds.
– The remainder of Group 13 elements are
generally considered to be metals, although some
compounds exhibit covalent characteristics.
❑Electropositive character /nature of the element in
this group increases from Boron to Aluminium and
then decreases from Aluminium to Thallium (why?)
8

9
value.
▪ REASON
▪ This increase of electropositivitity from Boron to Aluminium
is associated with increasing size.
▪ However, B and Al follows immediately after s block
elements, while Ga, In and Tl follows after d block elements.
▪ So the extra d-electrons in Ga, In and Tl do not shield the
nuclear very effectively, as a result their orbital electrons are
more tightly held and the metal are less electropositive.
▪ Evidenced by the increase of IE between Al and Ga even
though the large atom would be expected to have a9lower

10
OCCURRENCE AND EXTRACTION
➢ Group 13 elements are not found free in nature, but are all present
in various minerals and ores.
▪ Aluminiun is the most abundant metal in the Earth's crust
making up 8% existing in igneous rocks.
– Feldspars -(KAlSi3
O8
, NaAlSi3
O8and CaAl2
Si2
O8).
– Micas -given by general formula X2Y4-6Z8O20(OH, F)4 where X =
K, Na or Ca; Y = Al, Mg, Fe and Z = Si)
– Clays – occurs naturally, show plasticity through a variable range
of water content
e.g. Kaolinite, Al2Si2O5(OH) and Pyrophyllite, Al2Si4O10(OH)2 .
– Cryolite (Na3AlF6 – sodium aluminium fluoride)

11
– Spinel (MgAl2O4)
– Bauxite (Al2O3..H2O)
– Gemstone, which are impure form of the oxide of Al2O3
containing small amount of transition metals that give
them colours. E.g.
✓ Ruby: Al2O3 + traces of Cr3+
✓ Blue Sapphire: Al2O3 + traces of Fe2+, Fe3+ and Ti+4
✓White Sapphire: The germ from
aluminium itself
11

12
EXTRACTION OF ALUMINIUM
12

13
EXTRACTION OF ALUMINIUM
❑ Chief ore : Bauxite (Al2O3..nH2O)
❑ Impurities: Silica, Iron(III) Oxide,calcium Oxide And Titanium
Hydroxide, and other few oxides
❑ Additive: cryolite (Na3AlF6).
-Bauxite is dissolved in molten cryolite, Na3
AlF6 (Sodium
hexafluoroalumiminate) so as to lower its M.P
❑ Method: Electrolytic reduction
-Since Aluminium is reactive it is not extracted by chemical reduction e.g. C
……..as bauxite forms carbide.
-Usually produced by the electrolysis of bauxite.
❑ Electrolytic process: achieved by the Bayer – Hall Herout processes (…
major industrial process for production of Al)

14 14

15
Step 1:Digestion
▪ Ground metallurgical-grade bauxite is digested in caustic soda solution at
140 – 280°C in pressure tanks.
▪ Red mud is filtered off:
Al2O3 . 3H2O + 2NaOH →Na2O.Al2O3 + 4H2O + red mud
bauxite caustic soda Sodium Aluminate filtered
▪ NOTE: Except Alumina And Silica all other impurities (calcium oxide,
iron oxide, titanium oxide) DO NOT dissolve in the caustic soda liquor.
▪ The aluminate solution is filtered leaving behind the
impurities.
▪ Silica dissolved in the liquor is then precipitated from it by
slow heating. 15

16
Step 2: Precipitation
▪ Caustic soda is added to precipitate pure Al(OH)3
from Sodium Aluminate solution by seeding.
Na2O.Al2O3 + 3NaOH→2Al(OH)3.nH2O(s) +liquor
▪ Seeding of aluminum hydroxide reverses the
reaction
16

17
Step 3: Calcination
▪ "Hydrate", is calcined to form alumina .
▪ In the calcination process water is driven off to
form alumina, this takes place at 1050oC:
2Al(OH)3.3H2O(s) →Al2O3 + nH2O
▪ The calcination process must be carefully
controlled since it dictates the properties of the final
product.
▪ A large amount of the alumina so produced is
17
then subsequently smelted

18
Step 4 : Smelting (Electrolytic Reduction)
➢ Pure Al2O3 is dissolved in a molten Cryolite, Na3AlF6, in an
electrochemical cell.
▪
▪ Molten Cryolite lowers the M.P from above 2000°C to 950–
1000°C). to save energy operational cost.
At the cathode,
▪
- Al2O3 is reduced to molten Al.
At the anode
-Oxygen from the alumina reacts with the C electrode to form
CO2(g).
NB:The overall cell reaction is written as: 18
2Al2O3 (l) + 3C  4Al (l) + 3CO2 (g)

19
9
1
BAYER – HALL HEROUT PROCESSES

20
http://ibchem.com/IB/ibfiles/options/opt_E/ope_img/cell.jpg

21
Uses Of Aluminum
Use
Transport
Construction
Examples
Superstructures of trains, ships and airplanes. Alloy
engines for cars.
Window frames, doors roofing
Overhead electricity cables, capacitor foil
Kettles, saucepans
Power
transmission
Kitchen
utensils
Packaging Drink cans, foil wrapping
Chemical
industry
Al(OH)3 – flame retarder, paper making
2 4 3
Al (SO ) – flocculant in sweage treatment and to
precipitate PO43-
Al2O3 – catalyst and catalytic support material, abrasive

ENVIRONMENTAL IMPACT
▪ Smelting processes of aluminum requires enormous
amount of electricity.
▪ Also, the main process which is the electrolysis emits
carbon dioxide which is greenhouse gas.
▪ Recycling aluminum is an important method of
saving energy and minimizing the environmental
damage.
▪ Recycling aluminum requires only 5% of the energy
22

23
EXTRACTION OF BORON
23

24
➢Boron is found in ores widely distributed in
Earth's crust.
▪ Chief ore: BORAX……..the hydrated borates,
Na2B4O7.10H2O and similarly for tri, tetra and
pentaborates of calcium and sodium.
▪ Additive: Na or Mg to as reducing agents
…..reduces the oxides (B2O3)
OR using H2 in the presence of BCl3 and Tungsten
(W) filament 24

25
❖Extraction/Preparation of some boron
compound from Borax
25

26
❑GALLIUM, INDIUM AND THALLIUM
and
miner
➢The elements Gallium, Indium
Thallium are only found as
components of various minerals.
▪ These elements are produced or extracted
by electrolytic reduction in aqueous
solution
▪ They are relatively soft and
which readily dissolve in acids.
reactive,
26

27
PHYSICAL PROPERTIES
27

Property
Atomic number (Z)
B
5
Al
13
Ga
31
In
49
Tl
81
Outer electron configuration 2s22p1 3s23p1 4s23d104p1 5s24d105p1 6s24f145d106p1
Atomic rradii (pm) 80-90 143 122 167 170
Ionic radii (pm) 20 54 62 80 89
Electronegativity 2.37 1.50 1.60 1.70 1.80
Melting point (°C) 2300 660 29.7 156 304
Boiling point (°C) 3650 2467 2403 2080 1357
Density (g/cm3) 2.37 2.696 1.607 7.310 1.80
Ionization energies - 1st
Ionization energies - 2nd
Ionization energies - 3rd
M(s)  M3+(aq) + 3e-
Standard Reduction
Potentials (V, at 25°C)
M2+(aq) + 2 e-  M(s)
28
800.6 577.6 578.8 558 589.3
2427 1816 1979 1820 1970
3659 2744 2962 2704 2877
-0.87 -1.66 -0.53 -0.34 -0.72
Hardness - 2.75 1.5 1.2 1.25
Electroconductivity 59.7 9.1 19.0 82.882

29
▪ The M.P of all the elements are high,
- but the melting point of boron is much
higher than that of beryllium in Group 2
- M.P of aluminium is similar to that of
magnesium in Group 2 (diagonal
relationship).
▪ The densities of all the Group 13
elements are higher than those of Group
2 elements.
29

30
CHEMICAL PROPERTIES

31
➢The chemical properties of Group 13 elements
reflect the increasingly metallic character down the
group.
-Here only boron and aluminium will be considered.
▪Boron is chemically unreactive except at high
temperatures.
▪Finely divided boron burns in air to form oxide and
nitride:
4B(s) + 3O2(air) ® 2B2O3 (Oxide)
2B(s) + N2(air) ® 2BN (Nitride).
▪ Accordingly in halogen Boron form trihalides
2B(s) + 2X3(g) ® 2BX3. 31

32
❑GROUP 13 COMPOUNDS
▪ Because of their electron-deficient nature,
M3+compounds have a formally vacant npz
orbital and usually act as Lewis acids (electron
acceptors).
32

33
OXIDES (M2O3) -SESQUIOXIDE
▪ SESQUIOXIDE is an oxide containing three
atoms of oxygen with two atoms (or radicals)
of another element.
▪ The M2
O3of all the elements can be made by
heating the elements in oxygen:
4M (s) + 3O2(g) → 2M2O3 (s)
▪ But B2O3 is more usually made 33
by

34
34
B(OH)3
+H2O
100 oC
-H2O
+H2O
Red hot
-H2O
HBO2
Metaboric acid,
which exists in
three crystalline
forms of which
contains the cyclic
unit
B2O3
Boron oxide
Orthoboric acid
O
O B
O B
OH
OH
H
OH B
H

35
▪ H3BO3 is a weak acid……due to its electron deficient
tendency.
▪ The B(OH)3 accepts an OH- ion from the self ionization of
water forming a complex ion.
▪ by the
B(OH)3 + 2H2O → [B(OH)4]- + H3O+
The hydroxide boric acid B(OH)3 is formed
hydrolysis of many boron compounds.
▪ It has a layer structure made up of planar molecules linked
by hydrogen bonding (ref slide overleaf).
▪ It is a Lewis acid that acts as a Brønsted acid . 35

36
36
Oxidesofoxidationstate+3oftheGroup13Elements
O
x
i
d
e P
r
o
p
e
r
t
y
B
2
O
3
● Weakacid
● manymetaloxidesgivesglasses
withB2O3 asintheboraxbeadtest
Al2O3 andGa2O3 ● A
m
p
h
o
t
e
r
i
c
In2OandTl2O3
● Weakbasic
● Tl2O3givesO2 andTl2Oonheating
to100°C

37
HALIDES OF GROUP 13 ELEMENTS
BCl3 + H2O ¾→H3BO3 + 3HCl
▪ All elements form trihalides.
▪ They are nonpolar with trigonal planar shape.
▪The halides of boron are BX3 are all volatile, highly
reactive, covalently bonded molecular compounds and
are gases
▪The Boron fluoride (BF3) form fluoroborates, WHILE
other Boron halides giving boric acids
BF3 + H2O → [BF3OH] H
37

38
▪ BX3 are Lewis acids and the order of
their Lewis acidity strength is:
BF3 < BCl3 < BBr3
to the order of
of the attached
▪ In contrary
Electronegativity
halogens:
F > Cl > Br
38

39
▪ BX3 are trigonal planar and monomeric (not
dimerized in the way the BH3 does.)
E.g. the structure of BBr3.
39

40
electrons in its outer shell and can readily accept a
➢BF3 is a useful organic catalyst for Friedel Craft
reaction such as:
✓ Alkylations
✓ Acylation
✓ Estirification
✓ Polymerization of olefines
▪ REASON:
-Boron (an electron deficient atom) in BX3 has 6
40

41
▪ The fluorides of: Al, Ga, In, and Tl are
ionic having high melting points.
▪ The other halides of these metals are
covalent when anhydrous.
▪ AlCl3 , AlBr3 and GaCl3 exist as dimers
thus attaining an octet of electrons 41

42
▪ Exist as dimeric molecules with
the formula M2X6 using two
atoms to bridge the
halide
metals.
▪ This
retained
dimeric formula is
when the halides
dissolves in non-polar solvent
(e.g.; Benzene).
▪But because of high heat of
hydration when halides
dissolves in water, the covalent
dimer is broken into [M.6H2O42]
Figure. 1

43
▪ Aluminium chloride, AlCl3, is a volatile
solid which sublimes at 458K.
▪ The vapour formed on sublimation
consists of an equilibrium mixture of
monomers (AlCl3) and dimers (Al2Cl6).
▪ It is used to prepare the powerful and
versatile reducing agent lithium43

44
AlCl3 +
Lewis Acid
C2H5 – O – C2H5
dimethyl ether ( Lewis base )
44
▪ AlX3 (Aluminium halides) are very reactive lewis acids
– they accepts a pair of electrons forming an acid base
compound called adducts

45
▪ AlX3 is used as a catalyst in a number of
organic reactions.
E.G. When benzene is treated with acyl halide in
the presence of anhydrous Alcl3 as catalyst ¾®
aromatic ketone
45

46
▪ The B-X bond distances are shorter than might
be expected, and the B-X bond energies are
correspondingly higher.
E.g. B-F bond energy (646 KJmol-1) is the highest
known for a single bond.
▪
EXPLANATION:
This suggest that some π-bonding may be
existing between the unhybridized 2p orbital of
the boron and the filled np orbitals of the
halides.
46

47
HYDROXIDES
▪ Al(OH)3 is amphoteric and reacts with
acids in a manner as metal hydroxides do.
Al(OH)3 (s) + 3H3
O+ → [ Al( H2
O )6
]3
+(aq)
▪ Al(OH)3 also reacts with a base in the
reaction represented as the formation of a
hydro-complex
Al(OH)3 (s) + OH-  [ Al( OH )4
]-(aq4
)7

48
▪ When Al(OH)3 dissolves in a base, hydroxyl ion
and water bonds to Al ion forming a complex ion
[ Al( H2
O )2 (OH)4]-.
▪ The reaction is as follows
Al(OH)3
(s) + OH-(aq) + 2H2
O(l) → [Al(H2
O )2
(OH)4]-
▪ Al(OH)3 is used in the purification of water
because it carries down any suspended materi4a8l
in the water including most of the bacteria.

49
HYDRIDES
▪ Special compounds that start of predominantly
covalent and become more ionic as we go down the
group.
▪ Most of the group 13 elements react directly with
hydrogen, and large number of interesting hydrides
are known.
▪ Boron forms an extensive and interesting series of
hydrides, called BORANES.
▪ The simplest of these is not BH3as expected, but its
49
dimer B H .

50
▪ The 8 well characterized boranes which fall into two
series BnHn+4 and less stable series BnHn+6 are:
Diborane
Tetraborane
Pentaborane (stable)
Pentaborane (unstable)
Hexaborane
i. B2H6
ii. B4H10
iii.B5H9
iv.B5
H1
1
v. B6H110
vi.B9H15 Nonaborane (enneaborane)
vii.B10H14 decaborane 50

Cont…….
▪ The borane molecule (BH3) may exists as a reaction
intermediate.
▪ But no BH3as it does not exist as separate molecules. Boranes
are highly unstable due to their extreme electron deficiency.
▪ Their highly exothermic reaction with oxygen lead to their
consideration as rocket fuels by the space program
▪51
The simplest boron hydride that have been isolated is
▪ The B-atom in BH3 lacks the complete octet (i.e. it has only 6
electrons in the valence shell).
51

52
THE STRUCTURE OF B2H6 (DIBORANE) – MULTICENTRE
BONDS
▪The question of interest is what
holds the diborane together?
EXPLANATION OF THE STRUCTURE OF
B2H6.
▪There are 12 valence electrons at for
chemical bonding (B has 3, and H has
1, so 2  B + 6  H = 12)
•Each terminal B-H bond has two
electron bond, and there are fou5
r 2
of
then, thus accounting for a total of 8

53
▪ This leaves a total of four electrons to be
shared between the two bridging H
atoms and the two B-atoms.
▪ For this reason, two
bridging bonds are
B  H  B
formed, each
consisting two electrons forming the so
called three centre – two electron bond
(3C, 2e).
▪ Meaning that 3 atoms share 2 electrons
(This sometimes called banana bonds
because they non-linear but curved.
(Fig. below )
53

54
Figure 4. The Structure of B2H6 (diborane) – multicentre bonds.
54
Contains a 3-centre-2-electron bond (called a banana bond)

55
INDUSTRIAL INFORMATION / APPLICATION
➢Boron is used in:
✓ flares to provide a highly visible green colour.
✓Boron filaments are now used extensively in the
aerospace industry as a lightweight yet strong
material.
✓Boric acic acid is used as a mild antiseptic.
✓Borax as a water softener in washing powders.
✓Borosilicate glass contains boron compounds. 55

56