Elias lectures 2014 CYL 503 IITD
Name
Symbol
Elec. Config.
At. No At. Wt..
The p - block elements
Electronic configuration, Atomic number and atomic weights
2
Helium
He
1s 2
4.00
Boron
B
[He]2s 2 2p 1
10.81
5
Aluminum
13
Al
[Ne]3s 2 3p 1
26.98
Gallium
31
Ga
[Ar]4s 2 4p 1
69.72
Indium
49
In
[Kr]5s 2 5p 1
114.82
Thallium
Tl
[Xe]6s 2 6p 1
81 204.38
Carbon
C
[He]2s 2 2p 2
6 12.01
14
Silicon
Si
[Ne]3s 2 3p 2
28.09
32
Germanium
Ge
[Ar]4s 2 4p 2
72.64
Tin
50
Sn
[Kr]5s 2 5p 2
118.71
82
Lead
Pb
[Xe]6s 2 6p 2
207.20
Nitrogen
N
[He]2s 2 2p 3
7 14.01
15
Phosphorus
P
[Ne]3s 2 3p 3
30.97
33
Arsenic
As
[Ar]4s 2 4p 3
74.92
Antimony
51
Sb
[Kr]5s 2 5p 3
121.76
83
Bismuth
Bi
[Xe]6s 2 6p 3
208.98
Oxygen
O
[He]2s 2 2p 4
8 16.00
16
Sulfur
S
[Ne]3s 2 3p 4
32.06
34
Selenium
Se
[Ar]4s 2 4p 4
78.96
Tellurium
Te
[Kr]5s 2 5p 4
52 127.60
Polonium
84
Po
[Xe]6s 2 6p 4
209
Fluorine
F
[He]2s 2 2p 5
9 19.00
17
Chlorine
Cl
[Ne]3s 2 3p 5
35.45
35
Bromine
Br
[Ar]4s 2 4p 5
79.90
Iodine
53
I
[Kr]5s 2 5p 5
126.90
85
Astatine
At
[Xe]6s 2 6p 5
210
Neon
Ne
[He]2s 2 2p 6
10 20.18
18
Argon
Ar
[Ne]3s 2 3p 6
39.95
36
Krypton
Kr
[Ar]4s 2 4p 6
83.80
Xenon
Xe
[Kr]5s 2 5p 6
54 131.29
86
Radon
Rn
[Xe]6s 2 6p 6
222

in 2010
Among industrially important inorganic chemicals and chemical compositions, those based on the p block elements constitute a major component if one keeps the organic carbon based compounds aside.
Among the top fifteen bulk inorganic chemicals/elements produced by chemical industries across the world, ten belong to the p block.
1million metric ton (mmt) =1 000 000 000 kilograms (10 crore kg!)

S. No
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Bulk Inorganic
Chemical/Element/
Composition
Cement
Iron (steel)
Calcium carbonate/
Lime stone
Sulfuric acid
Ammonia
Sulfur
Sodium carbonate
Nitric acid
Sodium hydroxide
Glass
Chlorine
Hydrogen
Phosphoric acid
Aluminum
Hydrochloric acid
Year of reference
2013
2013
2008
2010
2013
2010
2012
2013
2004
2010
2010
2013
2009
2012
2005
Quantity
(world production in million metric tons)
3600
958(1528)
285
198
140
Major uses and applications
Construction
Construction, ships, containers etc
Metallurgy, building products, pulp and paper
Production of phosphate fertilizers from Fluorapatite
Fertilizers (80%), nitric acid synthesis
Sulfuric acid manufacture 77
62
60
60
56
Glass, detergents and cleaners, as source of sodium ion
Ammonium nitrate for use in fertilizers and explosives
Paper, detergents, Bayer process for aluminum
Construction, buildings, automobile
56
50
46
45
20
Ethylene dichloride, propylene oxide, isocyanates
Ammonia and methanol synthesis, petroleum refinery
Phosphate fertilizers
Construction, airplanes etc
PVC manufacture
1million metric ton (mmt) =1 000 000 000 kilograms ( 10 crore kg!)

The multibillion dollar chemical equation!
Ca
5
(PO
4
)
3
X + 5 H
2
SO
4
+ 10 H
2
O → 3 H
3
X=F (fluorapatite) OH hydroxyapatite)
PO
4
+ 5 CaSO
4
·2 H
2
O + HX

Examples of pesticides based on phosphorus and chlorine

Name
Material c-Si
Monocrystalline silicon p-Si
Polycrystalline silicon a-Si
Amorphous silicon
Bandgap
(300K) eV
Conv. efficiency
(%)
Type Advantages
1.1
19-22.5
1.1
1.7-1.8
13.0-16.0
11.1
Wafers (cut from cylindrical ingots)
Made by casting molten silicon
High conversion efficiency, long life.
Performs in low light
Process simple and less costly than c-Si. Lower heat tolerance than c-Si.
Thin films Mass production easy, flexible, cheap
Disadvantages
Very expensive, loss of material during cutting of ingots
Less efficient due to lower purity , lower space efficiency
Mostly small scale applications (e.g. calculators)
CdTe
Cadmium telluride
1.4
16.5-17.0
Thin films Cost efficient . large scale installation possible
Cadmium is highly toxic degrades
CIGS 1.
to
1.7
19.5-20.8
Thin films Flexible substrate, more efficient than CdTe
Less toxic than
CdTe, Degrades
Copper indium gallium selenide
Multi Junction (MJ)
Indium gallium phosphide;
Indium gallium arsenide;
1.9
1.4
40.7
Thin films Highest conversion efficiency. Application preferred in space
Most expensive.
Degrades fast
Germanium
0.7
The complete spectrum of sunlight, from infrared to ultraviolet, covers a bandgap range from approximately 0.5 eV to about 2.9 eV (red light 1.7 eV and blue light 2.7 eV).

Nuclear materials based on the p block
Lead can effectively attenuate certain kinds of radiation because of its relatively high density (11.3) and high atomic number. It is quite effective at stopping gamma rays, and X-rays. Lead’s high density is caused by the combination of its high atomic mass and the relatively small size of its bond lengths and atomic radius. Lead is ineffective in stopping beta particles because they can produce secondary radiation when passing through elements with a high atomic number and density (Bremsstrahlung). Instead, plastic can be used to form an efficient barrier for dealing with high-energy beta radiation before the radiation reaches the lead barrier. isotope
Indium -115
Boron-10
Cadmium- 113
Xenon- 135
Cross section for thermal neutron capture (barn)
100
200
30,000
2,600,000
Half life Natural abundance
4.41
× 10 14 years 95.71%
Non radioactive 19.9%
7.7 x 10 15 years 12.22%
9.14 hours 0 (Xe-135 is a decay product of I-135)

1935 H J Taylor
Aerial view of Chernobyl reactor

Transparent conducting oxides (TCOs)
Transparent conducting oxides (TCOs) are electrical conductive materials with comparably low absorption of electromagnetic radiation within the visible region of the spectrum. Indium tin oxide is one of the most widely used transparent conducting oxide because of its unique properties such as good electrical conductivity (~10 4 S/cm ), very high optical transparency
(75-90%), as well as the ease with which it can be deposited as a thin film. Indium tin oxide is a mixture of In
2
O
3
(90%) and SnO
2
(10%). The conductive and highly transparent surface created by ITO when applied as a coating to glass or other transparent surfaces, reflect infrared rays while allowing visible and UV light to pass.
ITO which has a stability upto 150  C is omnipresent in modern touch screen technology starting from automatic teller machines, touch screen mobile phones and tablet PCs. It is also used in flat panel LCD, OLED plasma and electro-chromatic displays, solar panels and even on the energy efficient windows of modern aircrafts for easy deicing.

Among the three, the one which has the highest market in terms of quantity are the silicones. The global market for silicones in terms of revenues was estimated to be worth $13,000 million in 2011 and is expected to reach $19,000 million by 2017.
The silicone market is dominated by elastomers and fluids, together accounting for over 80% of the overall market. Silicones possess superior properties and characteristics which are extremely useful in the automotive, construction, medical and personal care and, electrical and electronics end-user industries

Hydrophobicity
Wide temp range
Antifrothing
Oxygen permeability
Low glass transition temp
Non toxicity
First human foot print on moon
Moon temperature
(-153 to +107 °C)

Light Emitting Diodes
The main P-type dopant used in the manufacture of Light Emitting Diodes is Gallium and that the main N-type dopant used is Arsenic giving the resulting compound of Gallium Arsenide (GaAs) .The problem with using Gallium Arsenide on its own as the semiconductor compound is that it radiates large amounts of low brightness infra-red radiation (850nm-
940nm) from its junction when a forward current is flowing through it. But by adding Phosphorus, as a third dopant the overall wavelength of the emitted radiation is reduced to below 680nm giving visible red light to the human eye.
Semiconductor Wavelength Colour
GaAs
GaAsP
GaAsP
GaAsP:N
AlGaP
SiC
GaInN
850-
940nm
630-
660nm
605-
620nm
585-
595nm
550-
570nm
430-
505nm
450nm
Green
Blue
White
V
F
@ 20mA
Infra-Red 1.2v
Red 1.8v
Amber
Yellow
2.0v
2.2v
3.5v
3.6v
4.0v

Energy Efficiency
& Energy Costs
Life Span (average)
Watts of electricity used
(equivalent to 60 watt bulb).
Kilo-watts of Electricity used
(30 Incandescent Bulbs per year equivalent)
Annual Operating Cost
(30 Incandescent Bulbs per year equivalent)
Environmental
Impact
Contains the TOXIC Mercury
Carbon Dioxide Emissions
(30 bulbs per year)
Light Emitting
Diodes (LEDs)
50,000 hours
6 - 8 watts
Incandescent
Light Bulbs
Compact
Fluorescents
(CFLs)
1,200 hours 8,000 hours
60 watts 13-15 watts
329 KWh/yr.
3285 KWh/yr.
767 KWh/yr.
$32.85/year $328.59/year $76.65/year
No
451 pounds/year
No
4500 pounds/year
Yes
1051 pounds/year

As reagents and catalysts
Lewis acid catalysts based on main group metals such as aluminum, boron, silicon, tin and antimony (BF
3
, SnCl
4
, SiF
4
, SbF
5 and AlCl
3
) are used extensively in reactions such as Friedel-Crafts and the aldol reaction, and various pericyclic processes that proceed slowly at room temperature, such as the Diels-Alder reaction, Claisen rearrangement and acetal formation.
The unusual catalytic activity shown by aluminosilicates such as zeolites and clays
(e.g. montmorillonite) are unique to the p block elements. The open framework stable structures such as zeolites and ALPO can acts as dehydration and shape selective catalysts.
Also of importance are methylating agents such as AlMe
3 and its partially hydrolyzed product methyl alumoxane ( MAO ) which find application as cocatalysts in olefin polymerization reactions

Linde A
ZSM 5
Faujasite
Si 50% - Al 50%
Cations Na, Ca
Polar
3-D straight channels
Si 93 % non-polar
Hydrophobic
1-D channels
Si x% - Al y%
Cations Na, Ca
Polar
3-D entangled channels
Ring 8
Ring 10
Ring 12

7

Li= -3.0
F
2
=2.87
Inert pair efffect

Atomic radii of the elements

First Ionization energies highest

The rules are based on the Points on a sphere model as it envisages the arrangement of electron pairs as points on a spherical core. The rules have been quite successful in predicting the shape of compounds whose central atom is a p block element and not very useful in the case of compounds of transition metals .
Ronald Gillespie
Mc Master Univ., Canada
The " AXE method" of electron counting
A represents the central atom and always has an implied subscript one.
X represents the number of ligands (atoms bonded to A).
E represents the number of lone pairs surrounding the central atom.
The electrons are arranged in pairs that are either bonding (shared) pairs [X] or non bonding (unshared) pairs [E]. In the usual

-
 treatment this usually means ignoring the
 bonds temporarily since they will follow the
 bonds and therefore the two bonding pairs of a double bond or three bonding pairs of a triple bond are all primarily considered as a single point on the sphere. e.g. H
2
O AX
O=PCl
3
2
E
2
AX
4
2 bonding pairs and 2 lone pairs on Oxygen as central atom
4 bonding pairs
 bond ignored with phosphorus as central atom

The pairs of electrons in the valence shell adopt that arrangement which maximizes their distances apart.
This in other words means that the bonding and non bonding electron pairs are arranged as far apart from each other as possible on the surface of a sphere with the atom A at the centre of the sphere.
Rules which take care of the deviations observed from the ideal geometry
Rule 1: A non bonding lone pair [E] occupies more space on the surface of the central atom than a bonding pair [X]. In other words, lone pair- lone pair repulsion is greater than lone pair- bond pair repulsion which is greater than bond pair-bond pair repulsion. Lone pairs choose the largest site, e.g., equatorial in trigonal bipyramid and axial in pentagonal bipyramid. If all sites are equal, lone pairs will be better placed trans to each other.

Rule 2 : The strengths of the repulsions between bonds of different multiplicity decreases in the order: triple –double > double– double > double–single > single –single.
Rule 3 : Bonding pairs to electronegative substituents occupy less space than those to more electropositive substituents. Therefore angles between the single bonds, decrease with increasing electronegativity of the substituent.
This decrease in domain size with increasing electronegativity of the substituent happens as more of the bonding electron density is shifted to the electronegative substituent. In other words, the repulsion between single bonds decreases with increasing electronegativity of the substituent and/or decreasing electronegativity of the central atom.

Arrangement Bonding pairs
X
Linear 2
Lone pairs
E
0
Triangular
Tetrahedral
Trigonal bipyramid
3
2
4
3
2
5
4
3
2
0
1
0
1
2
0
1
2
3
Occupancy/
Steric number
Shape of the molecule
Examples
2 Linear AX
2
CO
2
, CS
2
, HCN, BeCl
2
, N
2
O, NO
2
+ ,
NCF, NCBr
3
3
4
4
4
5
5
5
5
Triangular planar
AX
3
Bent
(V shape) AX
2
E
Tetrahedral AX
4
Triangular
Pyramidal AX
3
E
SO
3
, BF
3
, COCl
2
, NO
BO
3
3-
3

, CO
3
2

,
SO
2
, O
3
, NOCl, SnCl
2
, PbF
2
, NOF
CH
4
NSF
NH
3
, SiCl
3
, ClO
, PCl
4
, SO
4

.
PO
2
Cl
2
4
3-
, POCl
3
, XeO
4
,
3
, SOCl
2
, IO
3

Bent AX
2
E
2
H
2
O, SCl
2,
[I(C
6
H
5
)
2
NSF,
] + , Kr
2
F
3
+
ICl
2
+ , SeCl
2
,
PF
5
, SF
4
O Trigonal
Bipyramidal AX
5
See saw
AX
4
E
Bent T shape
AX
3
E
2
Linear
AX
2
E
3
SF
4
, XeO
ClF
3
,
2
F
2,
IF
BrF
4
+
3,
, IOF
I(Ph)[(CF
3
C(O)O)]
2
3,
IO
2
F
2

XeOF
XeF
2
, I
3

, ICl
2

, BrF
2

. (C
6
F
5
)
2
Xe
2
,

Arrangement Bondi ng pairs
Octahedral
X
6
Pentagonal bipyramid
Square antiprism
5
4
7
6
5
8
Lone pairs
E
0
1
2
0
1
2
0
Occupancy
/
Steric number
6
Shape of the molecule
Examples
SF
6,
PF
6

,
SiF
6
2

,
AlF
6
3

, IF
6
+
6
6
7
7
7
0
Octahedral
AX
6
Square pyramidal
AX
5
E
Square planar
AX
4
E
2
Pentagonal bipyramid
AX
7
Pentagonal
Pyramid
AX
6
E
Pentagonal planar
AX
5
E
2
Square antiprism
AX
8
BrF
5,
[C
6
H
4
XeF
IF
7,
IF
8
-,
4,
XeF
XeF
8,
5
+
C(O)O] I(OAc)
3
IF
4

, XeOF
3

IO
2
F
5
2

, IOF
4

, TeF
5

IOF
6
, TeF
7
, CH
3
OTeF
6
,
(CH
3
O)
XeOF
5

2
XeF
XeF
6
5

XeF
8
2(AX
, SbF
8
E)
5
2

TeF
5
BiF
, IOF
5
2

7
2, SbF
[IF
5
7
2-
(C
6
H
5
)]

( monocapped octahedron)
, IF
5
2


Shapes of compounds having odd number of electrons
The odd electron also has an influence on the molecular geometry similar to a normal lone pair but of relatively lesser strength. As a result, the geometry will be midway between the molecule with a full electron pair and the molecule with one less electron pair on the central atom.
Nitrogen dioxide (NO
2
) (AX
2
E
0.5
) bent shape with an ONO angle 134

.
NO
2
 which is AX
2
E is also bent but has an ONO angle approximately of 120
 while NO
2
+ (AX
2
) is linear .
Similarly ClO
2 while ClO
2

(AX
2
E
1.5
) with a lone pair and an unpaired electron has OClO angle of with two lone pairs (AX
2
E
2
) has a OClO angle of 111

.
117.6

Exceptions to the VSEPR rules
1.
Metal complexes and organometallic compounds based on transition elements
2. Many triatomic alkaline earth metal dihalides , although expected to be linear have been found to be bent (approximate X-M-X angles: CaF
2
, 145°; SrF
2
, 120°; BaF
2
,
108°; SrCl
2
, 130°; BaCl
2
, 115°; BaBr
2
, 115° and BaI
2
, 105°). Gillespie has proposed that the reason for the same is due to loss of spherical symmetry of the inner shell of the metal
atom due to polarising effect of the relatively electronegative halide substituent’s.
Li
2
O also is linear although it is expected to be bent and this has been ascribed to the bonding being more ionic resulting in repulsion between the lithium atoms.

3. The silyl ether O(SiH
3
)
2 has a relatively larger Si-O-Si angle (144.1°), while similar bond angles of Cl
2
O (110.9°) and (CH
3
) expected range.
2
O (111.7°) are in the
Gillespie's rationalization for this observation is that the localization of the lone pairs, and therefore their ability to repel other electron pairs, is greatest when the ligand has an electronegativity similar to or greater than, that of the central atom.
When the central atom is more electronegative, as in O(SiH
3
)
2
, the lone pairs are less well-localised and have therefore a weaker repulsive effect.
4. Some molecules in which the central atom is from periods 3 and 4 and in which the ligands are less electronegative, do not have sufficient space in their valence shell to accommodate six bonding domains and a large lone pair domain. In such molecules the lone pair is squeezed into a spherical domain surrounding the core and inside the bonding domains ( stereochemically inactive s orbital ) which therefore have an octahedral arrangement. Thus some AX
6
SeCl
6
2and TeBr
6
2-
E molecule such as have a regular octahedral shape but with longer than normal bonds.

Some new developments
The electron pair domain model proposed by Gillespie and Harigittai in 1991 followed by Gillespie and Robinson in 1996.
This model was based not on pairs of electrons but on a region in space where there is more probability of finding an electron pair (bonding or lone pair ).
An electron pair domain is a region in space where there is an enhanced probability of finding an electron pair.
An electron pair domain extends around the most probable position of finding an electron pair as determined by the Pauli principle and the probability decreases on increasing the distance from the most probable position.
A lone pair domain can in general be thought of as more spread out and larger than a bonding pair domain as the electrons of a lone pair are subject to the attraction of only one atomic nucleus while those of a bonding air are subject to the attraction of two nuclei taking part in the bond formation .
A bonding pair domain therefore taken up less space around a nucleus compared to a lone pair domain because the former is stretched out more towards the ligand/ substituent of the central atom. Why a lone pair occupies more space than a bonding pair is well explained by the domain concept.

Ligand close packing model
The basis of this model is that the bond angles are determined by the packing of the ligands or substituents around a central atom . Irrespective of having lone pairs or not, the distance maintained between the substituents on a central atom will be almost same while the bond lengths and bond angles will be different as shown in the following examples.

423 BC 347 BC
Platonic Solids
Archimedian Solids