Answer Happy

I need to do a presentation on this essay it is about a
secondary bonding in material science at lest four slides for the
presentations : main points and definitions and
examples.
The process of combination (or) the attractive force between the
atoms within a molecule is called chemical bond. (or) A force that
acts between two (or) more atoms to hold them together as a stable
molecule is called chemical bond.
The three types of secondary bonding are van der Waals forces,
permanent dipole-dipole forces and hydrogen bonding.Secondary
bonding occurs due to forces produced by atomic or molecular
dipoles.
The dipoles are produced by random fluctuation of the electrons
around electrically symmetric atoms.
Another case of secondary bonding is caused when there exists a
permanent dipole in a molecule due to an asymmetrical arrangement
of positive and negative regions.
Molecules with a permanent dipole can either induce a dipole in
adjacent electrically symmetrical molecules (and thus form a weak
bond), or can form bonds with other permanent dipole molecules.
Hydrogen bonding is the stronger form of secondary bonding and
is formed from polar molecular bonding. These form, for example, in
water and hydrogen fluorides.
VANDER WAALS OR INTERMOLECULAR FORCES
Vander Waals forces are short-lived intermolecular attractive
forces, which exist between all kinds of atoms.. Vander Waals
forces are much weaker than both ionic and covalent bond. These
forces are electrical in nature and result from the attraction of
charges of opposite sign.
Factors affecting vander Waals forces
1. Molecular weight
As the number of electrons increases in a molecule, the
magnitude of the vender Waals forces increases. Since the molecular
weight varies directly with the number of electrons, vander Waals
forces increases with the increase in molecular weight and hence
boiling point increases.
2.Size of the molecule
When the size of the molecule increases, polarization increases
and hence vander Waals forces increases.
3. Temperature
Vander Waals forces decreases with increase int Temperature
i.e., at lower temperature the strength and magnitude of vander
Waals forces increases.
4.Pressure
Since temperature is inversely related to pressure, higher the
pressure, stronger will be the vander Waals forces.
TYPES OF VANDER WAALS FORCES
vander Waals forces arise from the following three main types of
interactions
1. Dipole Dipole interaction
2. Dipole Induced dipole interaction
3. Induced dipole Induced dipole interaction.
Dipole - Dipole Interaction
Exist: Between polar molecules i.e., HCl & HCl. The polar
molecules, though they are neutral, have a partial positive charge
at one end and a partial negative charge at the other end. So they
have permanent dipoles. The (+)ve end of the dipole attracts the
(-)ve end of the other dipole. These attractive forces (vander
Waals force) are referred to as dipole-dipole attractions
Examples:
H-CI. H-F, SO2, and NH3
Factors influencing Dipole-Dipole interaction
The magnitude of this type of interaction depends on
i. The dipole moment of the molecules.
ii. The greater the dipole moment, the greater is the
dipole-dipole interaction.
Dipole-Induced dipole interaction
Exist: Between polar molecules & non-polar molecule i.e.,HCI
& N₂
A polar molecule, (having permanent dipole) may polarise a
non-polar molecule, which is present in its vicinity and thereby
induce dipolarity in that molecule. The induced dipole then
interacts with the dipole of the first molecule and thereby the two
molecules are attracted together.example
i. Polar molecule : HCl, H-F, SO, etc.,
ii. Non-polar molecule : N₂, H₂, Br, etc
Factors influencing Dipole interaction Induced dipole
The magnitude of this type of interaction depends on
i. Magnitude of the dipole moment of the polar molecule, and
ii. Polarizability of the non-polar molecule.
Induced dipole-Induced dipole Interaction (or) Dispersive forces
(or) London forces
Exist: Between non-polar molecules, i.e., O, & Ng
In 1930, F. London first provided a simple explanation for the
existence of weak attractive forces between nonpolar molecules (or)
atoms. According to this view, electrons in a molecule are
constantly moving with respect to the nuclei of the atoms.Most of
the time electrons in molecules are distributed symmetrically. But
according to the principle of probability, at a given instant, the
electrons may concentrate on one side of the molecule than the
other molecule. This cause. the non-polar molecule (A) to become
momentarily self polarised called instantaneous dipole.
The negative side of the instantaneous dipole repels the
electrons of an adjacent molecule (B). As a result the second
molecule B also becomes a dipole by induced polarity. This is
called an induced dipole.
Factors influencing London forces
The strength of London force depends on how easily the electron
cloud in a particular molecule is deformed.
HYDROGEN BOND
In compounds of hydrogen with strongly electronegative elements
like fluorine, oxygen and nitrogen, the shared electron pair
between the atoms lies far away from the hydrogen atom (i.e.,
nearer to electronegative atom).
Example: Hydrogen fluoride molecule (HF)
In hydrogen fluoride molecule (HF), the shared. electron pair
between hydrogen and fluorine lies much more nearer to fluorine
atom. As a result, the fluorine atom acquires a fractional negative
charge; while the hydrogen atom acquires a fractional positive
charge. Such a molecule is said to be polar and behaves as a
dipole. Thus when two HF molecules approach closely, an
electrostatic force of attraction between such molecules will be
very strong. This attractive force between H atom of one molecule
and F atom of the other molecule leads to the formation of a weak
bond, called hydrogen bond or hydrogen bridge. The association of
two (or more molecules to form large clusters of molecules.
Definition
The attractive force which binds hydrogen atom of one molecule
with electronegative atom (like F, N, O) of another molecule of the
same substance is known as hydrogen bond or hydrogen bridge. It is
denoted by a dotted line.
10.6 TYPES OF HYDROGEN-BONDING
Hydrogen bondings are of two types
i. Intermolecular hydrogen bonding
ii. Intramolecular hydrogen bonding.
Intermolecular Hydrogen bonding
The electrostatic forces of attraction between hydrogen atom and
an electronegative atom of two different molecules is known as
intermolecular hydrogen bonding.
Intramolecular Hydrogen bonding
The electrostatic forces of attraction between hydrogen atom and
an electronegative atom present in the same molecule is known as
intermolecular hydrogen bonding.
Characteristics of the Hydrogen Bond
i. Hydrogen bond is longer and much weaker than normal covalent
bond.
Energy of hydrogen bond 10 k.cal/mole.
Energy of hydrogen bond 120 k.cal/mole
ii.Onlythe element having high electronegativity and small
atomic size (like O, N, F) are capable of forming hydrogen
bonds.
iii. Like a covalent bond, H-bond has a preferred bonding
direction.
iv. Since H-bond is electrostatic in nature, compounds
containing H-bond are partially polar
V. The molecules, joined to one another by H-bonds, have
unusually high boiling and melting points.
vi. The solubilities of the covalent compounds having H-bond are
high.
Conditions for the Formation of Hydrogen Bonding
The necessary conditions for the formation of hydrogen
bonding are
i. The electronegativity of the atom, bonded to hydrogen, should
be high.
ii. The size of the electronegative atom should be small.