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CHEM 120
WEEK 12 LECTURES
(INORGANIC WEEK 3)
Dr. MD BALA
Intramolecular Bonding
The bonding between molecules or atoms in the
solid state
Ionic bonding
e.g. sodium chloride
Covalent bonding
e.g. Graphite or diamond
Metallic bonding
e.g. copper/gold etc.
Van der Waals bonding
e.g. iodine or benzene
Hydrogen bonding
e.g. water and alcohols
IONIC BONDING
 Ions stack together in regular
crystalline structures.
 Typically ionic solids.
 Have high melting and
boiling points
 They are brittle.
 They form electrolyte
solutions if they dissolve
in water.
Ionic Solids
• The attractive force between a pair of oppositely charged ions
increases with increased charge on the ions and with decrease in
ionic sizes
requires less energy to
break up
Na+ = 99 pm
requires more energy to
break up
COVALENT BONDING
 Electron sharing
 Complete their octets by sharing electron pairs
F
F
e.g. Consider F2
The electronic configuration of F is 1s22s22p5
F
F
These are combined to form F2.
 Metallic bonding
 It is a special case:
• The electrons are considered
to be “delocalized”
• This gives rise to their
properties such as
malleability or ductility.
• Good thermal and
electrical conductors
Electrostatic forces and the reason ionic compounds
crack
Electrical conductance and ion mobility
Solid ionic
compound
Molten ionic
compound
Ionic compound
dissolved in water
van der Waals - Due to instantaneous dipoles
non-conducting species
Bond Polarity
• Covalent bonding between unlike atoms results in
unequal sharing of the electrons
– One end has larger electron density than other
• The result is bond polarity
– End with larger e- density gets partial - charge
– End that is e- deficient gets partial + charge
 H
••F 
Dipole Moment
Allotropy and Polymorphism
Allotropy:
e.gs. of elements and their allotropes
Polymorphism:
Bonding in other elements and their chemistries
Sulfur
• Rhombic and monoclinic are
different allotropes of sulfur
(same elements but different structural or molecular units)
Phosphorous
Linear molecule with triple bond
sp hybridized
Compounds of oxygen (oxides)
Acidity increases left to right
(metals form basic
ionic oxides)
(metalloids form
amphoteric oxides)
(non-metals form acidic
covalent oxides)
Acids and Bases
• Arrhenius definition:
- An acid provides H+ ions (ionizable hydrogen)
and a base produces OH- ions in an aqueous
solution
• Bronsted-Lowry:
- An acid is a proton donor and a base is a proton
acceptor
• Lewis acids and bases:
- An acid is a species that is an e- pair acceptor
and a base is an e- pair donor.
(base anhydride)
Anhydride means “without water”. A “base without water”
becomes a basic solutione when it reacts with water:
CaO (s) + H2O
base oxide
Ca2+ (aq) + 2OH- (aq)
calcium hydroxide
The oxide ion is protonated to produce the hydroxide:
O2- + H2O
2OH- (aq) (100%)
A basic oxide reacts with acids to produce water
CaO (s) + 2H+ (aq)
Ca2+ (aq) + H2O (l)
Oxoacids contain H
and O and one other
nonmetal
Sulfurous acid
Sulfuric
acid
base
acid
acid
base
tetra(hydroxo)aluminate(III) ion
Exercise
1. Write a balanced equation for Zn(OH)2 with:
a) an acid
b) a base
2. Does the following species act as an acid, a
base or an amphoteric species?
a) PO43b) CH3NH3+ = CH3NüH2 + H+
Oxoacids
Obtained from the dissolution of acidic oxides in water
e.g. CO2 + H2O = H2CO3(aq)
What are some Oxoacids?
What are polyprotic acids?
• They are acids with more than one ionizable
H atom per molecule
e.g. H3PO4
phosphoric acid (3 ionizable H
atoms
triprotic
H2SO4
sulfuric acid
diprotic
H2SO3
sulfurous acid
’’
H2CO3
carbonic acid
’’
Halogens as oxoacids
hypochlorite
chlorite
chlorate
perchlorate
especially
E0 = +1.61 V

 
H O Cl







- the hydrogen in HOCl is attracted to the lone pair on
oxygen atom in water
- water accepts a proton
base
- HOCl donates a proton
acid
Exercise:
a) What is the oxidation number of Cl in HOCl?
b) What is the oxidation number of Cl in OCl-?
c) What is the oxidation number of Cl in HClO4?
 Cl
Strengths of oxoacids
• How great is the pull of electrons away from
the O-H bond?
Affected by:
1. The electronegativity of the central atom
2. The no. of terminal O atoms in the acid
molecule
H O Cl
H O Br
ENCl = 3.0
ENBr = 2.8
Ka = 2.9 x 10-8
Ka =2.1 x 10-9
Which acid is stronger, H2SO4 or H2SO3?
O
O
H O S O H
H O S O H
O
Ka1a1==101033
-2
1.3xx 10
10-2
Ka1a1==1.3
Exercise
Which acid is stronger?
H O Cl O
O
H O
I O
O
Nitrogen
Nitrogen has oxidation nos. from -3 to +5
The most industrially useful states are:
-3 for ammonia NH3
0 molecular nitrogen N2
+5 for nitric acid HNO3
Physical description: NO is colourless,
paramagnetic (1 unpaired e-) and toxic
Generation of NO: Prepared by the action of Cu(II) salts on nitric
acid (HNO3):
colourless
nitrite(III
)
colourless
colourless

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