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Chapter 20
The Representative Elements:
Groups 5A Through 8A
20.1 Group 5A Elements
The Nitrogen Family
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ns2np3 valence
electrons
configuration
Nitrogen can
exist in many
oxidation states.
N and P are
nonmetallic.
As and Sb are
metalloid.
Bi is metallic.
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Bi and Sb tend to be metallic
But no ionic compounds containing Bi5+ and Sb5+
are known
BiF5, SbF5 and SbCl5 are molecular rather than ionic
G 5A elements can form molecules or ions that
involve 3, 5 or 6 covalent bonds to the G 5A atom
NH3, PH3, NF3, and AsCl3. They all behave as Lewis
base.
All G 5A elements except N can form molecules
(MX5) with 5 covalent bonds.
The ability of G 5A elements to form  bonds
decreases dramatically after N.
This is why N exists as N2 molecules; while other
elements in the group exist as larger aggregates
containing single bonds: P4, As4, Sb4
The Molecules of
the Types MX3,
MX5, and MX6
Formed by
Group 5A
Elements
The Structures of the
Tetrahedral MX4+ and
Octahedral MX6- Ions
20.2 The Chemistry of Nitrogen
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Since N2 molecule contains a triple bond, most
binary compounds (except NH3) containing N
decompose exothermically to the elements
In the preparation of NH3 from N2 and H2, too much
energy is needed to disrupt the N≡N bond.
Thus, though K (106) is high the reaction is very slow
at room temperature.
Haber process is used to prepare NH3 (high
pressure, high temperature and a catalyst are
needed)
Nitrogen fixation: The process of transforming N2 to
other nitrogen containing compounds
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Nitrogen fixation can be carried out by:
 Haber process (ammonia can be applied to the
soil as a fertilizer)
 High temperature combustion process in
automobile engines. NO produced is converted
into NO2 that with moisture is concerted into NO3that reaches soil.
 Natural. Lightning produces the energy that
disrupt N2 and O2 molecules producing reactive N
and O atoms that attack other molecules to form
nitrogen oxides that convert eventually to NO3 Nitrogen-fixing bacteria that reside on the root of
nodules of plants such as beans and peas. This
converts N2 to ammonia and other nitrogen
containing compounds.
Denitrification: return of N element to the
atmosphere as N2 gas. Bacteria changes NO3- to N2
The Nitrogen Cycle
Some Common Nitrogen Compounds
20.3 The Chemistry of Phosphorus
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Chemical properties of P are significantly different
from N for the following reasons:
 Nitrogen’s stability to form much stronger 
bonds
 Grater electronegativity of N
 Larger size of P atom
 Availability of empty valence d orbitals on P
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White phosphorus exists as P4: very reactive
and bursts into flames on contact with air.
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It is commonly stored under water
Black P and Red P are network solids
(a) The P4 Molecule Found in White Phosphorus
(b) The Crystalline Network Structure of Black Phosphorous
(c) The Chain Structure of Red Phosphorus
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P is essential for plant growth
Soluble phosphate fertilizer is made by treating
phosphate rock with sulfuric acid to make
superphosphate of lime, that is a mixture of :
CaSO4. 2H2O and Ca(H2PO4)2. H2O
A reaction of NH3 and P produces NH4H2PO4
a very efficient fertilizer
20.4 The Group 6A Elements
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The valence electron
configuration is ns2np4
Non of these elements
behaves as a metal
They achive the noble gas
configuration by adding 2
electrons to become 2anion
G 6A elements can form
covalent bonds with other
nonmetals
Due to the presence of
empty d orbitals (except
O), they form molecules in
which central atom is
surrounded by more than
8 electrons: SF4 and SF6
Group 7A
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ns2 np5 valence electron configuration.
All nonmetals
Reactive. Not free in nature. Found as halide (X-) ions.
Astatine radioactive with t1/2 = 8.3 hrs for its longest living
isotope
Very high electronegativities (4, 3, 2.8, 2.5 and 2).
Ionic bonds with metals and covalent bonds with
nonmetals in low oxidation states & polar covalent in
metals in high oxidation states.
Hydrogen Halides
HCl is the most important acid.
HF is used for etching glass.
SiO2(s) + 4HF(aq)  SiF4(g) + 2H2O(l)
X
H–X
Bond energy
(kJ/mol
F
Cl
Br
I
565
427
363
295
2O
X  ( g ) H

 X  ( aq)
Ho
Ho
(kJ/mol)
(J/mol.K)
-510
-159
-366
-96
-334
-81
-291
-64
Go
(kJ/mol)
+ 102.4
90
53
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Group 8A
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n2p6 configuration; Un-reactive.
He. Component of the sun.
Present in natural gas (from decay of radioactive
elements).
 Used as Coolant and a rocket pressurizing gas.
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Ne. Used in Luminescent lighting.
Ar. Used as a non-corrosive atmosphere in
light bulbs.
Xe & Kr form compounds with O and F.