here are short notes for the board and small competition.. good to memorize and revise..

1. CHEMICAL BONDING AND SHAPES OF MOLECULES By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
JUSTFORCHEMISTRY
rwtdgreat@gmail.com
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A place where you feel the CHEMISTRY
Octet Rule- During a chemical reaction the atoms tend to adjust their electronic arrangement in such a way that they
achieve 8 e
-
in their outermost shell. This is called octet rule.
Atoms in which d- orbital also participate in bonding can expand their octet for e.g. Phosphorous, Sulphur can
expend their octet, these are called hypervalent species.
For Lewis structure consider any standard textbook of Chemistry.
Chemical Bond- The force which keeps the atoms in any molecule together is called a chemical bond. [Overlapping
and De-overlapping of orbitals]
Ionic Bond- The columbic force of attraction which holds the appositively charged ions together is called an ionic
bond. An ionic bond is formed by the complete transfer of one or more electrons from the atom of a metal to an atom
of non- metal. NaCl, KCl, AgBr, [NH4
+
][Cl
-
] etc.
Lattice Enthalpy- The molar enthalpy change when the complete separation of the constituent particles that
compose of the solids (such as ions for ionic solid, molecules for molecular solids) under standard conditions is
called lattice enthalpy (ΔlHo). The lattice enthalpy is a positive quantity.
Electro valency- The number of electrons lost or gain by an atom of an element is called as electrovalency. The
element which give up electrons to form positive ions are said to have positive valency, while the elements which
accept electrons to form negative ions are said to have negative valency.
Formation of Ionic Bond- It is favored by- (i) the low ionization enthalpy of a metallic element which forms the
cations, (ii) High electron gain enthalpy of non- metallic element which forms the anions,
(iii) Large lattice enthalpy i.e; the smaller size and the higher charge of the atoms.
Covalency- The number of electrons which an atom contributes towards mutual sharing during the formation of a
chemical bond called its covalency in that compound.
Single Covalent Bond- A covalent bond formed by the mutual sharing of one pair of electrons is called a single
covalent bond, or simply a single bond. A single covalent bond is represented by a small line (−) between the two
atoms. Single bond sigma bond.
Double Covalent Bond [One sigma + one Pi] - A covalent bond formed by the mutual sharing of two pair of
electrons is called a double covalent bond, or simply a double bond. A double covalent bond is represented by two
small horizontal lines (=) between the two atoms. E.g. O=O, O=C=O etc.
Triple Covalent Bond [One sigma +two Pi] - A covalent bond formed by the mutual sharing of three pair of
electrons is called a triple covalent bond, or simply a triple bond. A triple covalent bond is represented by three small
horizontal lines (≡) between the two atoms. E.g. N≡N, H-C≡C-H etc.

2. CHEMICAL BONDING AND SHAPES OF MOLECULES By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
JUSTFORCHEMISTRY
rwtdgreat@gmail.com
www.slideshare.net/RawatDAgreatt
Google+/blogger/Facebook/Twitter-@RawatDAgreatt 9808050301
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A place where you feel the CHEMISTRY
Formation of Covalent Bond- It is favored by-
(i) High ionisation enthalpy of the combining elements.
(ii) Nearly equal electron gain enthalpy and equal electro-negativities of combining elements.
(iii) High nuclear charge and small atomic size of the combining elements.
Polar Covalent Bond - The bond between two unlike atoms which differ in their affinities for electrons is said to be
polar covalent bond. E.g. H-Cl
Co-ordinate Bond (Dative Bond) - The bond formed when one sided sharing of electrons take place is called a
coordinate bond. Such a bond is also known as dative bond. It is represented by an arrow (→) pointing towards the
acceptor atom. E.g. H3N→BF3
Formal Charge = No. of electrons in valance shell- no. of electrons in Lone pair- ½ no. of electrons in Bond pair.
Bond Length- Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a
molecule
Bond Angle- It is defined as the angle between the orbitals containing bonding electron pairs around the central
atom in a molecule/complex ion
Bond Enthalpy- It is defined as the amount of energy required to break one mole of bonds of a particular type
between two atoms in a gaseous state.
Bond Order- In the Lewis description of covalent bond, the Bond Order is given by the number of bonds between
the two atoms in a molecule.
In MOT bond order =
Where Nb = no. of electrons in BMO Na = no. of electrons in ABMO
Resonance- Whenever a single Lewis structure cannot describe a molecule accurately, a number of structures with
similar energy are consider to explain the various properties of molecule these structures are called the canonical
structures or resonating structures, of the hybrid which describes the molecule accurately.
Resonance gives stability to the system. Delocalization of electron occurs in Resonance.
Dipole Moment - The product of the magnitude of the charge and the distance between the centres of positive and
negative charge. It is a vector quantity and is represented by an arrow with its tail at the positive centre and head
pointing towards a negative centre.
Dipole moment (μ) = charge (Q) × distance of separation (d)
Dipole moment is charge separation. Its units are Debye (D) 1D= 1.33x10-30
C m
μ=0 for CO2, CCl4, BF3, CH4, BeF2, H2 μ of NH3 is More than that of NF3
Sigma Bond- A covalent bond formed due to axis-wise overlapping of orbitals of the two atoms, is called sigma (σ)
bond. For example, the bond formed due to s-s and s-p, p-p overlapping along the orbital axis are sigma bonds.
No nodal plane, overlapping zone 1.

3. CHEMICAL BONDING AND SHAPES OF MOLECULES By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
JUSTFORCHEMISTRY
rwtdgreat@gmail.com
www.slideshare.net/RawatDAgreatt
Google+/blogger/Facebook/Twitter-@RawatDAgreatt 9808050301
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A place where you feel the CHEMISTRY
Pi- Bond- A covalent bond formed by the side wise overlapping of p- or d- orbitals
of two atoms is called as pi (π) bond. For example, the bond formed due to the sideways overlapping of the two p-
orbitals is a pi- bond. Nodal plane present. Overlapping zone >1.
Hydrogen Bond- The bond between the hydrogen atom of one molecule and a more electro- negative element (like
F,O,N) of same or another molecule is called as hydrogen bond.
Two types of H-bonding are there- Intermolecular (requires two or more molecules) eg-
H2O-----H-O-H, H2N-H----NH3, HF---HF and intramolecular (within the same molecule) o- hydroxyl phenol, o-
nitrophenol etc
Hybridization- The process of energy mixing of the atomic orbitals to form orbitals of new energy is called
hybridization. All hybrid orbitals of a particular kind have equal energy, identical shapes and are symmetrically
oriented in shape.
 The hybrid orbitals are designed according to the type and the atomic orbitals merging together.
 Count bonds and lone pair in hybridization.
 No contribution from surrounding N and O.
To count electron pairs-
Electron pair Hybridization Co-ordination number Prefered Geometry
4 sp3 4 Tetrahedral
4 dsp2 4 square planar
3 sp2 3 Trigonal planar
2 sp 2 Linear
5 dsp3 or sp3d 5 Trigonal Bi Pyramidal [TBP]
6 d2sp3 6 Octahedral
VSEPR- Valence Shell Electron Pair Repulsion Theory which was given by Sidgwick and Powell in 1940 further
developed by Gillespie and Nyholm (1957).
 l.p. requires more space to adjust in 3D.
 l.p.- l.p. > l.p.-b.p. > b.p.-b.p. repulsion occurs b’coz bond contains electron clouds which are negatively
charged.
 In a molecule there should be minimum repulsion, electron pairs tend to occupy such position to minimize
repulsion, therefore adjustment occur in bond angles and actual shape differs from the predicted geometry.
 According to VSEPR if there are lone pairs of electron in any molecule, the actual shape comes differ as their
geometry.

4. CHEMICAL BONDING AND SHAPES OF MOLECULES By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
JUSTFORCHEMISTRY
rwtdgreat@gmail.com
www.slideshare.net/RawatDAgreatt
Google+/blogger/Facebook/Twitter-@RawatDAgreatt 9808050301
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A place where you feel the CHEMISTRY
Molecule Hybridization Predicted geometry and bond angle Actual shape and bond angle
CH4 Sp3 Tetrahedral 1090
28’ Tetrahedral 1090
28’(4 b.p.)
NH3 Sp3 Tetrahedral 1090
28’ Pyramidal 1070
(3 b.p. & 1 l.p.)
H2O Sp3 Tetrahedral 1090
28’ Angular or V-shape 104.50
(2 b.p. & 2 l.p.)
SF4 Sp3d Trigonal bi pyramidal (TBP) Distorted tetrahedral or Seesaw
[4 b.p. & 1 l.p.]
(l.p.at equatorial not at axial)
ClF3 Sp3d Trigonal bi pyramidal (TBP) Distorted T-shape [3 b.p. & 2 l.p.]
(l.p.at equatorial not at axial)
XeF2 Sp3d Trigonal bi pyramidal (TBP) Linear [2 b.p. & 3 l.p.]
(l.p.at equatorial not at axial)
VBT [Valence Bond Theory]- Given by Heitler & London(1927) further extended by Slater & Pauling.
Consider bonding b/w two atoms A and B.
 Attraction is there b/w Electrons of A and its nucleus and Similarly for B.
When A and B come into proximity-
 Nucleus of A attracts electrons of B and vice-versa.
 Electrons of A repel electrons of B and Nucleus of A repel nucleus of B.
 If attractive force overcomes the repulsive force, Bonding occur b/w A and B.
 In general bonding is an exothermic process.
 Lower the energy more will be the stability.
MOT [Molecular Orbital Theory] –
 LCAO (linear combination of atomic orbitals) give rise to the formation of molecular orbitals.
 The no. of MO formed is equal to the no. of AO participate.
 Half of the MOs are lower in energy called BMOs (bonding molecular orbitals) rest half those are higher in
energy, called ABMOs (anti-bonding molecular orbitals).
 The AOs combing should be comparable in energy as well as symmetry should
match to form MOs
 Electron filling follows the same rules as in case of AOs electron filling.
ψMO =ψa ψb
ψa and ψb are Atomic orbitals
A.O. M.O.
s
p
d
f

5. CHEMICAL BONDING AND SHAPES OF MOLECULES By Rawat Sir [M.Sc. Chemistry, 3 times NET (JRF), GATE ]
JUSTFORCHEMISTRY
rwtdgreat@gmail.com
www.slideshare.net/RawatDAgreatt
Google+/blogger/Facebook/Twitter-@RawatDAgreatt 9808050301
5
A place where you feel the CHEMISTRY
Upto 14 electrons remains below in bonding while for > 14 electron atom bonding is above and is below.
A.O’s A.O’s A.O’s A.O’sM.O’s
M.O’s