Interatomic forces present in atomic bonding can predict many
physical properties of materials ( i.e. melting temperature, elasticity,
thermal expansion, and strength).
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As two ions approach each other, each atom exerts forces on the
Magnitude of Forces is a function of interatomic distance
- Attractive Force, Fa
- Repulsive Force, Fr
Net Potential Energy between two
In assessing the performance of materials, it’s important to
draw attention to the relationship between material
properties and structural elements.
Finding the minimum of a Potential Energy Curve
corresponds to the energy released when two ions form a
bond, Bonding Energy.
Bonding Energy and shape of Potential Energy Curve vs. R
varies from material to material.
Number of material properties depend on E0.
Bonding is association of two atoms with in each
Interatomic bonding can be categorized as:
◦ Primary bonding
Primary bonds are also knows as chemical bonds.
Primary bonding necessarily involves the valence electrons
for its types.
The nature of bonds depends up on the electronic structure
of constituents atoms.
Primary bonding arises from the tendency of atoms to
assume the stable electronic structure like inert gases.
Types Of Primary Bonding
▪Coordinate covalent bond
»Ionic bond is due to electrostatic (columbic) forces of attraction
between oppositely charged ions.
» For two oppositely charged isolated ions, the attractive energy EA
is a function of inter atomic distance.
EA = A/r
A = [1/4 €)] [Z1e x Z2 e]
€ =Permittivity of vacuum
Ionic Bond Cont……
»Ionic bonds are formed where the difference in electro negativities of the constituent’s atoms is considerable.
» That̕ s reason ionic bonds are observed between the elements
situated at the horizontal extremities of the periodic table.
»In ionic bonds, bond energies generally range between 600 and
1500 kj/mole (3 and 8 eV/atom).
»NaCl is example of ionic bond.
» Covalent Bonds are formed by sharing of electrons between
» Two atoms of covalent bonds will contribute at least one electron
each, to the bond and chaired pair of electrons may be considered
to belong to both of them.
»Covalent bonds are favored between similar atoms
i.e. non-metallic elemental molecules (H2,O2,Cl2 etc.)
Covalent Bond Cont….
»Covalent bonds are also observed in molecules containing
dissimilar atoms such as CH4, H2O, HNO3 etc.
»Covalent bonds are found in diamond, silicon germanium and
right hand side of periodic table such as GaAs,SiC etc.
»The numbers of covalent bond that are possible for an atom are
determined by valence electrons.
Covalent Bond Cont…
» Covalent bonds may be very strong as in case of diamond (melting
point >3550 ºC).
» Covalent bond may be very week in case of Bismuth (melting
point ~270 ºC).
»It is found in polymers where basic molecular structure is a long
chain of carbon atoms which are covalently bonded with two of
their available 4 bonds per atom.
»e.g. in CH4.
Co-ordinate Covalent Bond
» A bond formed b/w two atoms when the shared pair of
electrons is donated by one of the bonded atoms is
called Co-ordinate Covalent Bond.
» Atom which donates pair of electron called donor atom
» Atom which accepts pair of electron called accepter
» e.g. bonding b/w BF3 & NH3.
Metallic Bonding is found in metals and their alloys.
Metallic atoms have one ,two or three valence electrons.
These valence electrons are not bound to any particular atoms in
They are more or less free to drift thought the entire metal.
Metallic Bonding Cont…
These electrons belong to the metals as a whole forming a sea of
electrons around different nuclei
These nuclei also called ion cores having a net positive charge which
is equal in magnitude to the total valence electrons charge per atom.
Free electrons act as a binder to hold the ion cores together.
Metallic bond is non directional in nature and bonding energy in
metallic bond may be strong or weak.
For example, bonding energy of mercury is 68 kj/mole and Tungston
has a bonding energy 850 kj/mole.
Secondary bond also known as physical bonds.
These are very weaker as compared to primary bonds.
Bonding energy are of order of 10 kj/mole.
It is more significant in noble gases which have stable electron
Secondary Bonding Cont…
Fluctuating induced dipole bonds
b) Polar molecule induced dipole bond
c) Dipole dipole bond
Fluctuating Induced Dipole Bond
Also known as London Dispersion Forces.
An atom is normally electrically symmetric means over all
distribution of electrons is symmetric.
As we know in constant vibration motion that can cause
instantaneous and short lived disturbance in electrical symmetry
for some atoms or molecules.
Resulting in creation of dipole.
Such dipole produces a displacement of electron distribution of
adjacent atoms or molecules which creates a dipole on second atom
Fluctuating Induced Dipole Bond
Resulting weak attractive forces between the two, these forces are
temporary and short lived.
These are the weakest bonds.
Polar Molecule Induced Dipole
Some molecules, have separation between negatively and
positively charged regions due to asymmetrical arrangement.
These molecules are termed as polar molecule.
These permanent dipoles arise due to the difference in the electro
negativities of the two atoms.
Polar molecules may also induced dipoles in adjacent non-polar
So bond will formed as a result of attractive forces between the
dipoles on two molecules.
Dipole Dipole bond
Vander Waal forces will also exist between polar molecules.
These forces called Dipole Dipole Bonds or Permanent Dipole
The associated bonding energy are significantly greater than for
bonds involving induced dipole.
Hydrogen bonding is a special case of permanent dipole bond.
Bonding energy incase of hydrogen bonding is 51 kj/mole.
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