Chemical Bond
•
•
•
A force of attraction that holds two atoms together
Has a significant effect on chemical and physical properties of
compounds
involves the valence electrons
Valence Electrons – the electrons in the outermost
energy level of an atom
-
This Lithium
Atom has one
valence electron
+
-
+ +
-
1
Counting Valence Electrons
-
-
-
+
+
+
-
-
+
-
+
-
++ +
+ + +
+
+
-
+
-
-
+
-
+ +
-
+
-
-
-
-
Carbon
Oxygen
Beryllium
4 valence
electrons
6 valence
electrons
2 valence
electrons
2
The Octet Rule
•
Atoms will combine to form compounds in order to reach eight
electrons in their outer energy level.
– Atoms with less than 4 electrons tend to lose electrons.
– Atoms with more than 4 electrons tend to gain electrons.
•
Be aware that there are some exceptions!
CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS!
3
The Octet Rule In Action
6
-
7
-
-
-
5
Notice how this chlorine atom has
seven valence electrons, one away
from eight. It will try to gain one
more according to the Octet Rule.
-
-
-
+++
+
++ + +
+ ++ ++
+ +
++
-
4
-
-
1
-
3
-
-
-
-
-
-
1
-
-
++
+++ ++
+
++ +
2
Notice how the sodium atom has
one valence electron. It is this
electron that it will try to get rid of
according to the Octet Rule.
-
-
-
-
-
Where do you think Chlorine finds that one electron that it needs?
4
Bonds
Ø Ionic bond
Ø Covalent bond
Ø Metallic bond
Ø Hydrogen bonding
Ø Non-covalent Interactions / Electrostatic Interactions
Ø Stacking
Ø Lone pair – 𝛑
Ø Cation – 𝛑
Ø Anion – 𝛑
5
IONIC BONDS
•
•
•
•
The force of attraction between oppositely charged ions.
Occurs after a transfer or loss/gain of electrons
Usually form between atoms of metals and atoms of nonmetals
Resulting compounds have a name that usually ends in –ide
Cl
Na 1+
1-
-
-
-
-
-
-
-
-
++ +
+ + +
+
+
-
-
-
-
-
+
-
++ +
+ +
+
+
-
-
-
-
-
-
Example - Sodium Chloride (NaCl)
-
6
COVALENT BOND
•
•
•
A force that bonds two atoms together by a sharing of
electrons
Each pair of shared electrons creates a bond
Usually occurs between atoms of non-metals
H O H
-
+
++ +
+ + +
+ +
-
-
-
+
-
-
Example – Water (H2O)
7
Types of Covalent Bonds
• Different covalent bond types share a different
number of electrons
Water (H2O)
-
Carbon Dioxide (CO2)
Nitrogen (N2)
-
-
-
-
+
++ +
+ +
+
+
+
+
++ +
+ +
+
+
-
-
-
-
- - -
++
+ +
+
+
-
-
-
-
-
-
-
-
-
- - -
++ +
+ + +
+
+
-
-
+
+
+ +
+
-
-
-
++
- - - -
++
+ + +
+
+
-
-
+
Single Bonds
Share 2
Electrons
Double Bonds
Share 4
Electrons
Triple Bonds
Share 6
Electrons
8
Unequal Sharing
(Polar Covalent Bond)
•
The unequal sharing of electrons between two atoms that
gives rise to negative and positive regions of electric charge
+
+
Bonded hydrogen
atoms showing
equal sharing of
electrons
Electron
Cloud
++ +
+ + +
+ +
+
Hydrogen and
fluorine bond with
an unequal sharing
of electrons
Why do you think the two Hydrogen atoms share
equally, but the Hydrogen and fluorine do not?
9
Electronegativity
10
Polar Covalent Bonds
The greater the
difference in
electronegativity,
the more polar is
the bond.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
13.
14.
15.
16.
17.
Bags and Phones must be left near the entrance
After leaving the bag and phone, you will pick up a sheet.
The sheet will be numbered and sealed.
You should just go to particular seat and wait for me to tell you to open it.
You should not open till I say.
You need to sit for the whole duration.
The number is big and the window is just an hour.
I need your full cooperation.
Think before circling the answer(s).
Can’t change after circling.
Please do not make a stampede.
If you do not make me happy, then I cannot keep you happy.
Your neighbor will have a different set of questions.
So no need to look at them at all.
DAP students should come to me directly and I will give you seats.
All the best.
1
Basic Inorganic Chemistry – I: Bonding
The metallic radius of a metallic element is defined
as half the experimentally determined distance
between the centres of nearest-neighbour atoms in
the solid
The covalent radius of a nonmetallic element is similarly
defined as half the internuclear distance between
neighbouring atoms of the same element in a molecule
We shall refer to metallic and covalent radii jointly as
atomic radii
The ionic radius of an element is related to the distance
between the centres of neighbouring cations and anions
in an ionic compound.
The radius of the oxide ion is taken to be 140 pm.
For example, the ionic radius of Mg2+ is obtained by
subtracting 140 pm from the internuclear distance
between adjacent Mg2+ and oxide ions in solid MgO.
Basic Inorganic Chemistry – I: Bonding
The valence bond theory (VB theory) of bonding was the first
quantum mechanical theory of bonding to be developed.
Valence bond theory considers the interaction of atomic orbitals
on separate atoms as they are brought together to form a
molecule.
Although the computational techniques involved have been largely
superseded by molecular orbital theory, much of the language and
some of the concepts of VB theory still remain and are used
throughout chemistry.
Basic Inorganic Chemistry – I: Bonding
Electrons in atomic orbitals of the same symmetry but on neighbouring atoms
are paired to form 𝛔 and 𝛑 bonds.
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Molecular orbital theory
Ø VB theory provides a reasonable description of bonding in simple molecules
Ø VB theory does not handle polyatomic molecules very elegantly
Molecular orbital theory (MO theory) is a more sophisticated model of
bonding that can be applied equally successfully to simple and complex
molecules.
In MO theory, we generalize the atomic orbital description of atoms in a very
natural way to a molecular orbital description of molecules in which electrons
spread over all the atoms in a molecule and bind them all together
Ø Molecular orbitals are constructed as linear combinations of atomic
orbitals
There is a high probability of finding electrons in atomic orbitals that have large
coefficients in the linear combination
Ø Each molecular orbital can be occupied by up to two electrons
Basic Inorganic Chemistry – I: Bonding
• Orbital Interactions: In MO theory there are two ways for
orbitals to interact with each other and form two types of
orbitals
• Bonding molecular orbital: an additive combination where
orbitals combine to form a shape resembling the
combination of both orbitals. It is lower in energy than the
original orbitals. Denoted as σ or π depending on the bond
type.
• Anti-bonding molecular orbital: a subtractive combination
where orbitals do not combine to form one shape, but from
a node between each other. It is higher in energy than the
bonding orbital and original orbitals. Denoted
as σ* or π* depending on the bond type.
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Molecular Orbital Diagram of Helium
Basic Inorganic Chemistry – I: Bonding
Molecular Orbital Diagram of Lithium
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Molecular Orbital Diagram of Fluorine
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Acknowledgement
Shriver & Atkins’ Inorganic Chemistry
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Molecular Orbital Diagram of Helium
Basic Inorganic Chemistry – I: Bonding
Molecular Orbital Diagram of Fluorine
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
The procedure can be summarized as follows:
1. From a basis set of four atomic orbitals on
each atom, eight molecular orbitals are
constructed.
2. Four of these eight molecular orbitals are 𝞂
orbitals and four are 𝝿 orbitals.
3. The four 𝞂 orbitals span a range of energies,
one being strongly bonding and another
strongly antibonding; the remaining two lie
between these extremes.
4. The four 𝝿 orbitals form one doubly
degenerate pair of bonding orbitals and one
doubly degenerate pair of antibonding orbitals.
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
5
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Bonding
Basic Inorganic Chemistry – I: Anion-Pi
Basic Inorganic Chemistry – I: Cation-Pi
Basic Inorganic Chemistry – I: Cation-Pi
Basic Inorganic Chemistry – I: Cation-Pi
Basic Inorganic Chemistry – I: Bonding
Sequestration using Lone Pair···π Interactions
R4
R3
R5
O
S
S
R2
O
S
N
R2
O
S
R1
R1
R3
S
R4
O
S
O
O
N
δ+
S
O
O O
S
R5
N
R1
R5
S
O
R4
R2
R3
O
0.5 −
O
S
0.5 −
O
O
Gaseous Guests
dCg-Cg = 8.816 Å
BP: -10 °C;
TL: 110 °C;
ΔT: 120 °C
12