chemical bonding and molecular structure

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Akarshik Banerjee
Pratyush Dey
Sayantan Biswas
Class- X l ’B’

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Matter is made up of on or different elements.
But under normal conditions except noble gasses
no other elements occur as single atom.
Evidently there is a force which holds together
various constituent particles in different
chemical species.

This force is called the-

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Octet Rule
As per electronic theory of chemical bonding atoms
combine to attain noble gas configuration.

Covalent Bond
When two or more atoms share electron pairs they are
said to be covalently bonded.

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Lewis dot structures provide a picture
of bonding in molecules and ions in
terms of shared pairs of electrons and
octet rule.
A few examples are-

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Formal charge on each O atom are:On O no.1= 6

- ½ - ½ (6)=1

On O no. 2= 6

– 4 – ½ (2)=0

On O no.3= 6 – 6 – ½ (2)=

-1

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The incomplete octet of central
atom.
Odd electron molecules.
The expanded Octet.

When two or more elements form a bond by complete transfer of
electrons the bond is said to be electrovalent bond.

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ClIt is defined as the energy required to
completely separate one mole of solid
ionic compound to gaseous constituent
Na+
ions.
Covalent radius is measured as the radius
of an atom’s core which is in contact with the
core of adjacent atom in bonded situation.
Van der Waals radius represents the overall
size of the atom which includes its valence shell
in non –bonded situation.
Bond angle is the angle between the
orbitals containing the electron pairs around
the central atom/molecule/ complex ion.
Bond enthalpy is the energy required to
break one mole of like bonds in two atoms in
gaseous state.
Bond order is the no. of bonds between two
elements in a molecule.

rC
rv

dw

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Whenever a single Lewis structure cannot
describe a molecule accurately, a no. of structures
with similar energy, positions of nuclei, bonding &
non bonding pairs of electrons are taken as the
canonical structure of the hybrid which describes
the molecule accurately.

Resonance in CO3-2 represent the three canonical
forms:-

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In heterogeneous covalent compounds due to greater
electronegativity of one atom the shared electron pair
ins displaced more towards it than the other molecule.
As a result of polarization the molecule posses a net
Dipole moment (depicted as a small arrow with the
tail in the positive center and head on the negative
center.)

Dipole moment = charge

x

distance of separation

By knowing the dipole moment the symmetry or the
polarity of a molecule can be known.
The net Dipole moment of NF3 is less than NH3
despite fluorine being more electronegative is due
to the fact that the arrows are in opposite
directions in both cases and the lone pair adds to
the dipole moment in the latter but decreases the

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The shape of a molecule depends upon the no. of valence
electrons.
Pairs of electrons repel each other.
They tend to occupy such positions so as to minimise
repulsion and maximise distance between them.
The valance shell is taken as a sphere .
A multiple bond is treated as a single electron pair and
single electron pairs in multiple bonds are treated as a
single super pair.
The VESPER model is applicable to any such structure
where two or more resonance structures can represent a
molecule.

VSEPR Theory is able to predict the geometry of
large no. of molecules especially the compounds of
p-block elements accurately.

Geometry of molecules in which central atom has no
lone pair

Geometry of molecules in which central atom has 1 Or more lone
pairs

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As two atoms approach each other the following
forces come into action:Attractive forces betweena) Nucleus of an atom & its own electrons.
b) Nucleus of one atom & electrons of the other
atom.
Repulsive forces betweena) Electrons of two atoms.
b) Nuclei of two atoms.
The valance bond theory explains the directional
properties of bond as a consequence of inter
electronic repulsion.

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p-p overlapping (sigma
Bond)
s-p overlapping (sigma
Bond)
p-p overlapping (pi
Bond)
s-s overlapping (sigma Bond)

Strengths – The strengths of bonds depends upon the extent of
overlap. So sigma bond has more strength than pi bond.

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Hybridisation is the process of intermixing of the orbitals of
slightly different energies in order to redistribute their energies
to form new set of orbitals with equivalent energy and shape.

S-p hybridisation
It involves mixing of 1S
orbital and 1p orbital

S-p 2 hybridisation
and 2p orbitals.

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S-p 3 hybridisation
and 3p orbitals.

Hybridisation involving
d orbitals
S-p 3 d hybridisation

S-p 3 d 2 hybridisation

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The electrons in various molecules are present in
molecular orbitals.
The atomic orbitals of comparable energy and symmetry
combine to form molecular orbitals.
The molecular orbitals are polycentric.
The no. of molecular orbitals formed is equal to the no.
of atomic orbitals taking part in combination.
The energy of the bonding molecular orbitals are less
than the energy of the non bonding orbitals thus the
bonding orbitals are more stable.
The electron probability distribution around a group of
nuclei in a molecule is called a molecular orbital.
It obeys aufbau principle , Hund’s rule and Puali’s
exclusion principle.

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In O2 molecule
In H2 molecule
He2 molecule
H2

O2

He 2

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The hydrogen bond can be defined as the attractive force
which binds hydrogen atom of one molecule with the
electronegative atom of another molecule.
When bonded with a strong electronegative atom the
hydrogen atom acquires partial positive charge as the
electron gets displaced more towards the electronegative
atom. This causes formation of polar molecule having
electrostatic force of attraction. They can be either:(1)Intermolecular
Or,
(2)Intramolecular

The name of the slide designer is on top
left corner of every slide:

A

for

Akarshik (rollno. 5)

S

for

Sayantan (rollno. 24)

P

for

Pratyush (rollno. 21)

Hope the project was decent……. Thanks
for watching.

chemical bonding and molecular structure

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