Include boron, aluminum, gallium, indium and thallium.
Boron is the only nonmetal in the group many of their compounds of the elements are electron deficient and act as Lewis acids. Aluminum is a metalloid
And gallium, indium and thallium are metals.
He
Li Be
C N O F Ne
Mg
Si
Ca
Ge
Sr
Sn
Ba
Pb
Ra

Covalent radius/pm
Metallic radius/pm
Ionic radius(M +3 )/pm
Melting point/ °C
Boiling point/ °C
1 st I.E.I
1
/kj.mol
-1
80
27
2300
3930
799
2 nd I.E.I
2
/kj.mol
-1
3 rd I.E.I
3
/kj.mol
-1
2427
3660
Electron affinity,
E a
/kj.mol
-1
26.7
Pauling electronegativity 2.0
E ө
(M 3+ ;M)/V -0.89
125
143
125
141
150
166
155
171
53
660
2470
577
1817
2745
62
30
2400
579
1979
2963
94
157
98
304
2000 1460
558 590
1821 1971
2704 2878
42.5
28.9
28.9
1.5
-1.68
1.6
-0.53
1.7
1.8
-0.34
+1.26
Page 288 Sh&At

Electronic configuration – ns 2 np 1 Generally exhibit +3 oxidation state and changes to +1 as the group is descended.
Covalent, metallic and ionic radii increases from B to Tl.
Electronegativity: Ga is more electronegative than Al due to the alternation effect . (consequence of increased nuclear charges of the 4p elements due to the presence of their poorly shielding 3d electrons.
Distinct chemical properties from those of other elements in a group:
- Boron forms acidic oxides, B
2
O
3
, and aluminium forms amphoteric oxide, Al
2
O
3
- Boron forms polymeric oxide structure.
- Boron form flammable, gaseous hydrides, aluminium hydride is a solid
- Boron is electron deficient and making all its neutral compounds Lewis acids.

Element
Boron
Symbol I
E
(kJ.mol
-1 )

Electronic
Configuration
B 801 2.0
[He] 2s 2 2p 1
Aluminium Al
Gallium
Indium
Thallium
Ga
In
Tl
577
579
558
590
1.5
[Ne] 3s 2 3p 1
1.6
[Ar] 3d 10 4s 2 4p 1
1.7
[Kr] 4d 10 5s 2 5p 1
1.8
[Xe] 4f 14 5d 10 6s 2
6p 1
Oxidation state
III*
(1)
I
I
I*
III*
III*
III*
III

Boron
-1
334
757
536 423 220
Aluminium 284 664 511 444 370
Gallium
Indium
274
243
577
506
481 444
439 414
339
331
Thallium 188 445 372 334 272
Al – most abundant and Tl and In are least abundant.
B:- Borax; Na
2
Borax - Na
2
B
4
B
O
4
O
5
(OH)
4
.8H
2
O and kernite; Na
5
(OH)
4
.8H
→reduced with Mg, hydrofluoric acid, HF
2
B
4
O
2
O → boric acid, B(OH)
3
5
(OH)
4
.2H
2
O;
→ boron oxide, B
2
O
3
Pure boron is produced by reduction of BBr
2 BBr
3
(g) + 3 H
2
3 vapour with H
(g) → 2 B(g) + 6 HBr(g)
2
:
Al:- clays and aluminosilicate minerals and commercially as bauxite.
Gallium oxide occurs naturally as an impurity in bauxite and indium is obtained in the Pb and Zn ores. Thallium compounds are found in the flue dust.

Al is the widely used nonferrous metal, it’s light, has high electrical and thermal
Conductivity and high reflectance. Small percentages (less than 2 %) of other metal gives desirable weight to strength ratio.
Al/Mn – most widely used and contains Fe and Si in traces to give added strength and hardness
Al/Mg – have good ductility and corrosion resistant but less strong.
Al/Si – have good fluidity and used in welding wires.
Al/Li – have very low density and high elasticity.
Al/Cu/Mg – used in making aircrafts.
Al/Cu – used in satellites and space vehicles.
Other uses of Al alloys include building and construction – walls, gutters, window frames, roofs and doors, aerosol cans, drink cans, sheets and foils and cooking utensils – toys, tools, refrigerators, cosmetic tubes and airconditioning units and in cars – body panels, engine blocks, wheels, bumpers and radiators.

First step: Purification of the ore – Bayer’s process.
Bauxite is crushed and digested with caustic soda under pressure.
Al
2
O
3 dissolves to form sodium aluminate.
Extraction
Al
2
O
3
.
3H
2
O + 2NaOH 2NaAlO
2
+ 4H
2
O decomposition or
Al
2
O
3
.
3H
2
O + 2NaOH 2Na[Al(OH)
4

The solution is diluted thereby impurities like TiO
2
, sodium aluminium silicate and iron(III) oxide precipitate out. They are filtered out.

CO
2 is bubbled through the liquor to reduce the pH to enable Al(OH)
3 precipitate and then filtered and washed.

Al(OH)
3 is calcined at ~1300 ° C to give pure Al
2
O
3
+ 3H
2
O.
2Al(OH)
3
Al
2
O
3
+ 3H
2
O

This is done by electrolysis using the HallHéroult process.
Al
2
O
3 is dissolved in molten cryolite, Na
3
[AlF
6
] and electrolysed in a graphitelined steel tank which serves as the cathode and carbon as anode.
Calcium fluoride (fluospar) is added to lower the m.p.
Molten aluminium (m.p. 600) is drained from the bottom of the cell at intervals.
Cryolite is made synthetically to augment the mined cryolite.
2Al(OH)
3
+ 3NaOH + 6HF

Na
3
[AlF
6
] + 6H
2
O
(Cryolite improves the electrical conductivity of the cell as Al
2
O
3 is a poor conductor. It also serves as an added impurity and lowers the m.p. of the mixture to about 900 ° C).

Typical electrolyte composition ranges are Na
3
[AlF
6
] (80-85%), CaF
2
AlF
3
(5-7%), Al
2
O
3
(2-8% - intermittently recharged).

The following dissociations occur;
(5-7%),

2AlF
3
Al
2
O
3
Al
3+
+ AlF
6
3-
AlO
2
-
+ AlO
+
; AlO
+
Al
3+
+ O
2-

Al is preferentially discharged at the cathode and oxygen at the anode.
Al
3+
+ 3e
2AlO
2
-
Al
Al
2
O
3
+ ½O
2
+ 3e
Carbon anode burns to CO
2
, so the anode is replaced periodically.
Some aluminium fog dispersed in the electrolyte, reduces CO2 to CO. Exit gases contain about 30% CO. The overall anode reaction seems to be
Al
2
O
2
F
4
2+ 2AlF
6
3+ C

4AlF
4
+ CO
2
+ 4e and at the cathode
AlF
6
3+ 3e

Al + 6F -
Overall cell reaction:
3Al
2
O
2
F
4
2+ 10AlF
6
3+ C

12AlF
4
+ 3CO
2
+ 4Al + 24F -

Cryolite and Fluospar
Series of carbon anodes
Steel casing cathode
Aluminium tapped and transferred to reverbaratory furnace before being cut into inguts.

Figure 12.12 page 304
Boron hydride compounds – Borane, the simplest form is diborane – B
2
H
6 its structure is described as 2c,2e and 3c,2e bonds; can be prepared by metathesis of boron halides with either LiAlH
4 or LiBH
4 in ether.
3 LiBH
4
(et) + 4 BF
3
(et) = 2 B
2
H
6
(g) + 3 LiBF
4
(et)
All the boranes are electron deficient, colourless and diamagnetic.
Higher boranes are classified according to their electron count:
Type
Closo
Nido
Arachno
Hypho
Formula
B n
H n
2-
B n
H n+4
B n
H n + 6
B n
H n + 8 skeletal electron pairs Examples n + 1 n + 2 n + 3 n + 4
B
5
H
5
2to B
12
H
12
2-
B
2
H
6
, B
5
H
9
, B
6
H
10
B
4
H
10
, B
5
H
11 none

Wade’s Rules: established by Kenneth Wade in the 1970s based on correlation between the number of electrons, the formula and the shape of the molecules.
This apply to a class of polyhedra called deltahedra because they are made up of triangular faces resembling Δ. For molecular and anionic boranes - predict shapes of molecule or anion from its formula.
H
H
H
B B
B-H bonds – 2c-2e
B-H-B bonds – 3c-2e
H H H
Diborane, like all boranes, is electron-deficient. There are 12 electrons (6 from
H and 3 each from B). The four B-H bonds use 8 electrons, leaving 2 electrons each for the B-H-B bonds. The B-H-B bonds are therefore electron –deficient
(short of 4 electrons)

•
2
3
•
•
•
H
H
H
B
H
B
-
H
B
4
H
10
B
-
H
H
H
B
-
H
H
+
2 :NH
3
H
H
H
B
-
H
N
+
H H
H
N
+
H
+
H
H
H
B
-
B
-
H
H
H
B
-
H
H

BORON TRIHALIDES
Are useful Lewis acids as a result of incomplete octet, with BCl
3 stronger than
BF
3
. They consist of trigonal planar BX
3 molecules. BCl
3
, BF
3 are gases; BBr
3 is a volatile liquid and BI
3 is a solid.
B(OH)
3
B(NH
2
)
3
B(OR)
3
H
2
O
Protolysis
RNH
2
ROH
BX
3
PR
3
NR
3 Complex formation
SR
2
X
3
BPR
3
X
3
BNR
3
X
3
BSR
2
REACTIONS OF BX
3
COMPOUNDS

BORON OXYGEN COMPOUNDS
Important oxides – B
2
O
3
, polyborates and borosilicate glasses.
2 B(OH)
3
(s) Δ→ B
2
O
3
(s) + 3 H
2
O(l)
An example of cyclic polyborate anion, [B
3
O
6
] 3- three coordinate B atom and [B(OH)
4
] four coordinate B atom. Polyborates form by sharing O atom with the neighboring B atom. The rapid cooling of molten B
2
O
3 lead to the formation of borate glasses.
Sodium perborate, commonly written as NaBO
3
.4H
2
O contains peroxide ion –
O
2
2, and hence the accurate formula is Na
2
[B
2
(O
2
)
2
(OH)
4
].6H
2
O. It is used as a bleach in laundry powders, automatic dishwashing powders and whitening toothpaste.
O
-
O
B
O
H O
O
OH
B
-
O
O
-
B
O
B
O
-

LEWIS ACIDITY
Diborane and other hydrides act as Lewis acids and cleaved by reaction with
Lewis bases;
2
2
6
6
3
3
3
3
4
-
2
3
3
3
2
+
HYDROBORATION, METAL BORIDES – SUPERCONDUCTING ABILITY OF MgB
2
METALLABORANES, CARBORANES

LiAlH
4 and LiGaH
4 sources for H are good precursors for metal hydride complexes, MH ion for the metalloid hydrides – SiH
4
3
L
2
. Aluminium hydride, AlH
3 and is a solid similar to the s-block metal hydrides although not readily available. Pure
Ga
2
H
6 has been prepared recently and the hydrides of Tl and In are very unstable.
Some of the reactions involving the hydrides:
- 4 LiH + ECl
- LiAlH
- LiEH
- (CH
3
4
4
)
3
3
+ SiCl
4
N-EH
3
→ (Δ, ether) LiEH
4
→ (THF) LiAlCl
+ [(CH
3
)
3
+ N(CH
3
)
3
4
NH]Cl → (CH
3
)
3
→ ((CH
3
)
3
+ LiCl (E = Al, Ga)
+ SiH
N-EH
N)
2
3
4
+ LiCl + H
EH
3
2
(E = Al, Ga)
+ LiCl + H
2
(E = Al, Ga)

All elements form trihalides in their +3 oxidation state, however +1 becomes
Common with Tl forming a stable monohalide. Trihalides of Al, Ga and In are
Lewis acids. Generally prepared by reaction of the electropositive metal with hydrogen halides such as HCl, HBr gases.
2 Al (s) + 6 HCl (g) → (100 °C) AlCl
3
(s) + 3 H
2
(g)
Trifluorides are mechanically harder than others and they have high melting points and sublimation enthalpies and have low solubility. Their reactivity towards most donors is low (not Lewis acids) and despite that AlF
3 and GaF
3 form slats such as Na
3
AlF
6
(Cryolite)
– used as a solvent for bauxite in the production of aluminium) and Na
3
GaF
6
.

Thallium trihalides are less stable than those of light congeners. The triiodide,
TlI3 is a compound of +1 and +3 as it contains the I3- not the I- ion. Confirmed by the standard electrode potentials which indicates that Tl(III) is rapidly
I reduced to Tl(I) by iodide:
Tl 3+ (aq) + 2 e → Tl + (aq) E
Ө
= +1.26 V
3(aq) + 2 e → 3 I (aq) E
Ө
= +0.55 V
However, in excess iodide Tl(III) is stabilized by the formation of the complex;
TlI
3
(s) + I → TlI
4
(aq)
Generally the +1 oxidation state becomes more stable progressively from Al to
Tl.
(Read more in page 310)

Al and Ga form α and β forms of oxide in which the elements are in their +3 oxidation state; Tl forms an oxide in which it’s in +1 oxidation state and a peroxide. α-alumina, Al
2
O
3 is the most stable form and is very hard and a refractory material. In mineral form called corundum and as a gemstone is called sapphire, ruby, emerald or amethyst depending o the amount of metal ion impurities. Dehydration of Al(OH)
3 at temperatures below 900 °C result in the formation of γ-alumina, which is metastable polycrystalline form with a defect spinel structure. The α and γ forms of Ga
2 analoques. The metastable form is β-Ga
2
O
3
O
3 have the same structureas their Al
, which has a ccp structure with
Ga(III) in distorted octahedral and tetrahedral sites. In forms In
2
O
3 and Tl forms
Tl(I) oxide and peroxide, Ti
2
O and Tl
2
O called alums – MAl(SO
4
)
2
.12H
2
2
. The elements all form a series of salts
O where M is univalent cation such as Na + ; K + ;
Rb + ; Cs + ; Tl + or NH
4
+ . Alums are thought of double salts containing the hydrated trivalent cation [Al(H
2
O)
6
] 3+ . The remaining water molecules form hydrogen bonds with the sulfate and the cations.

+3 Ox. State B
2
O
3
Al
2
O
3
Ga
2
O
3
In
2
O acidic amphoteric amphoteric basic
3
+1 Ox. State
Tl
2
O
3 basic
Tl
2
O basic
Al
2
O
3 and Al(OH)
3 are amphoteric
Al (OH)
3

3H

(aq)

Al
3

(aq)

3H
2
O (Al(OH )
3 a base)
3


(aq)

4
-
(aq)
3
3

( aq )

2
6
3


Ga
2

In
2
O
O
3
3 and Ga(OH) and Tl
2
O
3
3 are amphoteric and dissolve in alkali to form gallates.
are completely basic and the metals form neither hydrates nor hydroxides.

TlOH is a strong base and is soluble in water, like Group 1A hydroxide.

Tl + compounds are extremely poisonous and in large doses, can cause death.

The only sulfide of Al, Al
2
S
3
, which is prepared by direct reaction of the elements at elevated temperatures: 2 Al(s) + 3 S(s) → (Δ) Al
2
S
3
(s). It is rapidly hydrolyzed in aqueous solution; Al
2
Al
2
S
3
S
3
(s) + 6H
2
O(l) → 2Al(OH)
3
(s) + 3H
2
S(g)
, exists in three different forms – α, β and γ forms. The structure of α and
β forms are based on wurtzite structure in α–Al
2
S
3 the S 2ions are hexagonal close packed and the Al 3+ ions occupy two-thirds of the tetrahedral sites randomly. The γ-form adopts the same structure as γ-Al
2
O
3
. The sulfides of Ga,
Tl and In are numerous and varied than those of Al and adopt many different structural types.
Al, In and Ga react with P, As and Sb to form materials that are semiconductors

GaS
α-Ga
2
S
3
γ-Ga
InS
β-In
TlS
Tl
4
S
2
S
3
3
2
S
3
Layer structure with Ga-Ga bonds
Defect wurtzite structure
(hexagonal)
Defect sphalerite structure
(cubic)
Layer structure In-In bonds
Defect spinel ( γ-Al
2
O
3
)
Chains of edge-shared Tl III S
4 tetrahedra
Chains of Tl III S
4 tetrahedra and Tl I Tl III S
3
g
GaAs 1.35
GaSb
InAs
InSb
Si
0.67
0.36
0.163
1.107