Polarity of bond, Polarity of molecules, Intermolecular forces

1. PRESENTATION ON POLARITY
AND BONDS
• PRESENTED PRESENTED
• BY; TO
• PAVADHAARANI.K Dr.T.PRABHA

2. Physical properties
• The three main properties of a molecular substance
include:
• Low melting point
• Temperature that indicates when a solid substance
changes to a liquid;
• Boiling point, or a temperature that indicates the
point at which a liquid changes to a gas, or vapor;
poor conductivity; and low solubility,

3. Chemical properties
• Chemical bonds are the electrical forces of attraction
that hold atoms or ions together to form molecules.
• Different types of chemical bonds and their varying
intensity are directly responsible for some of the physical
properties of minerals such as hardness, melting and
boiling points, solubility, and conductivity.
• Chemical bonds also influence such other properties as
crystal symmetry and cleavage.
• Strong bonds between atoms make them more difficult
to separate and, in general, stronger chemical bonds
result in greater hardness

4. Polarity of bonds
the state of having two opposite or contradictory
tendencies, opinions, or aspects

5. Polarity refers to the physical properties of compounds
such as boiling point, melting point and their
solubilities.
The polarity of bonds is caused due to interaction of
bonds between molecules and atoms different
electronegativity.
Polarity in chemistry is nothing but the concept of the
separation of electric charges leading a molecule to
have a positive and negative end.

6. • Consider an. Example.. In a H-F bond,the fluorine
atom is more electronegative than that of
hydrogen atom.The electrons eventually spend
more time at the fluorine atom.
• Hence,this Flourine atom slightly becomes
negative whereas the hydrogen atom tends to
become slightly positive

7. Polar molecules
• Polar molecules occur when two atoms do not
share electrons equally a covalent bond.
• A dipole forms, with part of the molecule carrying a
slight positive charge and the other part carrying a
slight negative charge.
• This happens when there is a difference between
the electronegativity of each atom.

8. Non polar molecules
• When molecules share electrons equally in a
covalent bond there is no net electrical charge
across the molecule.
• In a nonpolar covalent bond, the electrons are
evenly distributed.
• You can predict nonpolar molecules will form when
atoms have the same or similar electronegativity.

9. Types of bonds

10. Non polar covalent bonds
• Nonpolar covalent bonds are a type of bond that occurs when two
atoms share a pair of electrons with each other.
• These shared electrons glue two or more atoms together to form a
molecule.
• Like children who share toys, atoms involved in a nonpolar covalent
bond equally share electrons
• . An example of a nonpolar covalent bond is the bond between two
hydrogen atoms because they equally share the electrons.
• Another example of a nonpolar covalent bond is the bond between
two chlorine atoms because they also equally share the electrons.
• Nonpolar covalent bonds are very strong bonds requiring a large
amount of energy to break the bond.

12. Polar covalent bonding
• Polar covalent bonding is a type of chemical bond
where a pair of electrons is unequally shared
between two atoms.
• In a polar covalent bond, the electrons are not
equally shared because one atom spends more
time with the electrons than the other atom.
• In polar covalent bonds, one atom has a stronger
pull than the other atom and attracts electrons.

14. Polar molecule
A polar molecules has a net
dipole moment as a result of the
opposing charges(i.e.partial
positive and partial negative
charges)
Water is an example of polar
molecules since it has a slight
positive charge on one side and a
slight negative charge on other.

15. To calculate electronegativity

16. Properties of polar molecule
• If the difference in electronegativity for atoms in a bond is
greater than 0.4 we consider the bond as polar if the
difference is less than 0.4,the bond is essentially non-polar
• In polar molecule,the ends of the molecule, called
dipoles,carry an unequal charge.
• This is an important concept because many areas of the
body are either water soluble or fat soluble.
• A polar molecule is water soluble

17. Melting point
• The melting point of a substance is the temperature
at which it changes state from solid to liquid.At the
melting point the solid and liquid phase exist in
equilibrium.
• The melting point of a substance depends on
pressure and is usually specified at a standard
pressure such as 1atm
• When considered as the temperature of the reverse
change from liquid to solid ,it is referred to as the
freezing point or crystallization point.

18. • However, substances can be cooled below their
freezing point without the formation of a solid.
Such liquids are known as supercooled liquids
• Because of the ability of some substances to
supercool, the freezing point is not considered as a
characteristic property of a substance.

20. Melting points (in blue) and
boiling points (in pink) of the first
eight carboxylic acids

21. Polarity of molecules
• Polarity in molecules is the separation of electric
charge leading to a molecule or its chemical groups
having an electric dipole moment, with a negatively
charged end and a positively charge end.
• Polarity molecules must contain polar bonds to
differences in electronegativity between the
bonded atoms.

23. Kofler Bench
• A Kofler bench is a metal strip with a temperature
gradient (range from room temperature to 300 °C).
Any substance can be placed on a section of the
strip, revealing its thermal behaviour at the
temperature at that point.

24. Intermolecular forces
• Intermolecular forces are the forces which mediate
interaction between molecules, including forces of
attraction or repulsion which act between molecules and
other types of neighbouring particles
• Intermolecular forces are weak relative to intramolecular
force-the forces which hold a molecule together.
• For example, the covalent bond,involving sharing electron
pairs between atoms,is much stronger than the forces
present between neighbouring molecules.
• Both sets of forces are essential parts of force fields
frequently used in molecular mechanics

25. The investigation of
intermolecular forces starts from
macroscopic observations which
indicate the existence and action
of forces at a molecular level

26. Types of forces
• Attractive intermolecular forces are categorised
into the following types:
• Hydrogen bonding
• Ionic bonding
• Ion-induced dipole forces
• Ion-dipole forces
• Van der Waals force - keesom force,Debye
force,and London dispersion force

27. Hydrogen bonding
A hydrogen bond (often informally abbreviated H-bond) is a
partial intermolecular bonding interaction between a lone
pair on an electron rich donor atom, particularly the
second-row elements nitrogen (N), oxygen (O), or fluorine
(F), and the antibonding molecular orbital of a bond
between hydrogen (H) and a more electronegative atom or
group
Such an interacting system is generally denoted by Dn-
H...Ac the solid line denotes a polar covalent bond
And the dotted or dashed line indicates the hydrogen
bond

28. • Hydrogen bonding is a special type of dipole-
dipole interaction that occurs between the lone
pair of a highly electronegative atom
• This type of bond can occur in inorganic molecules
such as water,DNA and proteins
• Intramolecular hydrogen bonding is partly
responsible for the secondary and tertiary
structures of proteins and nucleic acid. It also plays
an important role in the structure of polymers,
both synthetic and natural.

32. Ionic bonding
• Ionic bonding is a type of chemical bonding that involves
the electrostatic attraction between oppositely charged
ions, and is the primary interaction occurring in ionic
compounds
• It isone of the main types of bondingalong with covalent
bonding and metallic bonding. Ions are atoms (or groups
of atoms) with an electrostatic charge.
• Atoms that gain electrons make negatively charged ions
(called anions). Atoms that lose electrons make positively
charged ions (called cations)

33. • In the simplest case, the cation is a metal atom and
the anion is a nonmetal atom,but these ions can
be of a more complex nature, e.g. molecular ions
like NH4+ and SO42-
• In simpler words, an ionic bond results from the
transfer of electrons from a metal to a non-metal
in order to obtain a full valence shell for both
atoms.

34. • If the metal and non-metal starts to form a bond,
the opposite charges they will cancel each other
• In ionic bonds,total positive charge equals the
total negative charge to form a neutral ionic
compound
• These oppositely charged ions are attracted to each
other to form a lattice in three dimensions

36. • In example of Nacl,the molecules if dissolved in
water, the Na metal is surrounded by water
molecules with oxygen molecules oriented towards
it,and the cl non-metal is surrounded by molecules
of hydrogen.
• This is because if these oppositely charged
molecules when dissolved conduct electricity.
• Not all the ionic molecules are dissolved in water

37. Comparison of electronegativity of
bonds
• Type of bond. Difference in electronegativity
• Non polar covalent <0.4
• Polar covalent. 0.4-1.7
• Ionic. > 1.7

38. Ion induced dipole forces
• An ion-induced dipole attraction is a weak attraction
that results when the approach of an ion induces a
dipole in an atom or in a nonpolar molecule by
disturbing the arrangement of electrons in the
nonpolar species.
• The ion induced dipole force is a permanent effect in
polar molecules because of presence of dipoles
• Ex:H2O the hydrogen carries positive charge and
oxygen carries negative charge so there is a diploe
already present there

40. • In this example,the ion has to be present to induce
a dipole that causes the neutral molecule to occupy
positive charge on one side and negative charge on
other side

41. Ion dipole forces
• An ion-dipole force is an attractive forces results from the
electrostatic attraction between an ion and a neutral
molecule that has a dipole.
• Most commonly found in solutions. Especially important for
solutions of ionic compounds in polar liquids.
• A positive ion (cation) attracts the partially negative end a
neutral polar molecule.
• A negative ion(anion) attracts the partially positive end a
neutral polar molecule.
• Ion-dipole attractions become stronger as either the charge
on ion increases as the magnitude of the dipole of the polar
molecule increases.

43. Van der Waals forces
• Van der Waals forces include attraction and repulsion between
atoms, molecules, and surfaces, as well as other intermolecular
forces.
• They differ from covalent and ionic bonding in that they are
caused by correlations in the fluctuating polarizations of nearby
particles
• Being the weakest of the chemical forces,with a strength
between 0.4 and 4kJ/mol, they may still support an integral
structural load when multitudes of such interactions are present.
• The force results from a transient shift in electron density
• It exists in all molecules but more dominant in non-polar
molecules

44. • The main characteristics of van der Waals forces are
• They areweaker than normal covalent and ionic bonds.
• Van der Waals forces are additive and cannot be saturated.
• They have no directional characteristic.
• They are all short-range forces and hence only interactions
between the nearest particles need to be considered
(instead of all the particles). Van der Waals attraction is
greater if the molecules are closer
• Van der Waals forces are independent of temperature
except dipole – dipole interactions.

46. • In the example shown the non-polar molecule ,the electrons
are equally distributed in electron cloud with positively
charged nucleus at centre
• As the electrons start to move there is distribution of
charges,,so one side of the atom becomes + and other side
becomes - and finally it becomes polarised
• It causes the other atom to become polarised in the same
the way,the + charge of the second atom faces the - charge
of first atom and vice-versa
• If electrons in an atom increases the molecular weight
increases which in turn increases the vanderwaals force.

48. Boiling point
• The boiling point of a substance is the temperature at which
thevapour pressure of a liquid equals the pressure
surrounding the liquid and the liquid changes into a vapor.
• The boiling point of a liquid varies depending upon the
surrounding environmental pressure.
• A liquid in a partial vacuum has a lower boiling point than when
that liquid is at atmospheric pressure.
• A liquid at high pressure has a higher boiling point than when
that liquid is at atmospheric pressure.
• For example, water boils at 100 °C (212 °F) at sea level, but at
93.4 °C (200.1 °F) at 1,905 metres (6,250 ft) altitude

49. • For a given pressure, different liquids will boil at
different temperatures.
• The normal boiling point (also called the
atmospheric boiling point or atmospheric pressure
boiling point) of a liquid is the special case in which
the vapor pressure of the liquid equals the defined
atmospheric pressure at sea level,one atm

51. Solubility
• Solubility is a property referring to the ability of the
given substance the solute, to dissolve in a solvent.
• It is measured in terms of the maximum amount of
solute dissolved in a solvent at equilibrium.
• The resulting solution is called a saturated solution.
• Solubility depends on the temperature and pressure
and it also depends on nature of solute and solvent.,it
has no units
• A solute dissolves in a solvent if intermolecular
interactions are similar in two substance

52. • In saturated solution,if dissolution process is
exothermic (∆H is -ve), solubility decreases with
increase in temperature.
• If dissolution process is endothermic (∆H is +ve)
solubility increases with increasing temperature.
• Since liquids and solids are highly incompressible,
pressure has no effect on dissolution of solids or
liquids in liquid solvent, many gases are soluble in
water.

53. • Solubility of gas in water generally decreases with
increase in temperature and pressure,the no of
gaseous molecules per unit volume over solution
increases
• At constant temperature, the solubility of gas in
liquid is directly proportional to pressure of gas

54. Henry was the first to give
quantitative relationship
between the solubility and
pressure of gas which is known
as. Henry's law
C=K× P
C is the concentration of liquid
K is Henry's constant
P is partial pressure

55. Dalton,concluded that solubility
of gas in liquid is a function of
partial pressure of gas
Pt=Pa+Pb+Pc
Pt is total pressure
Pa is pressure of gas1
Pb is pressure of gas2
Pc is pressure of gas3

56. Ionic and non-ionic compound
• Ionic compounds are two or more ions held together
by attraction. An example of an ionic compound is
table salt.
• It consists of positive sodium ions and negative
chloride ions that is a crystal that can be seen with the
naked eye.
• If it looks like it is a powder it is just because the
crystals are too small to actually be seen.
• They have high melting and boiling point and are hard
or brittle,they can also be dissolved in water
• Ex:Nacl

57. • Ions in ionic compounds are primarily held together by
the electrostatic attraction between the charge
distribution of these bodies,
• In particular the ionic bond resulting from the long long-
ranged Coulomb attraction between the net negative
charge of the anions and net positive charge of the
cations
• In a reaction between metals to lose electrons and non
metals to gain electrons to complete their octet.
• Metals and non-metals generally react to form ionic
compound.

59. Non ionic compound
• The definition for a non ionic compound is simply
means that the chemical bonds are non ionic
• All the compounds having non-ionic bonds such as
theLondon forces, covalent bonds etc are known
as a non-ionic compound.
• These compounds are formed by the sharing of
electrons between the atoms.
• For example:H2,O2 etc

61. Protic solvent
• protic solvent is a solvent that has a hydrogen atom
bound to an oxygen (as in a hydroxyl group), a nitrogen
(as in an amine group), or fluoride (as in hydrogen
fluoride).
• In general terms, any solvent that contains a labile H+
is called a protic solvent.
• The molecules of such solvents readily donates
protons(H+) to solutes, often via hydrogen bonding.
Water is the most common protic solvent.
• Ex:water,ethanol, methanol, ammonia

63. Aprotic solvent
• Conversely, aprotic solvents cannot donate
electron.
• Aprotic solvent is a solvent that doesn't have O-H
and N-H bond.
• The "a" means without and "protic" refers to
proton or hydrogen means that they do not form
hydrogen bonds but they can accept hydrogen
bonds.
• Ex:acetone , acetonitrile

65. Ion pairs
• ion association is a chemical reaction whereby ions of
opposite electrical charge come together in solution to
form a distinct chemical entity.
• Ion associates are classified, according to the no of ions that
associate with each other, as ion pairs,ion triplets
• Ion pairs are also classified according to the nature of
interaction as contact, solvent-shared,or solvent-
separated.
• Ion pairs does not exist in ideal solution because all ions are
separated from one another by solvent molecules

66. The most important factor to
determine the extent of ion
association is the dielectric
constant of molecule. Ion
associates have been
characterized by means of
vibrational spectroscopy. The
concept was introduced by Niels
Bjerrum.

68. • By an IUPAC definition, solvation is an interaction
of a solute with the solvent which leads to
stabilization of the solute species in the solution

70. • When there is about one solvent molecule between
cation and anion and, the ion pair may be termed
solvent shared.

72. • when the ions are in contact with each other, ion
pair is termed a contact ion pair. Even in a contact
ion pair, however, the ions retain most of their
solvation shell.

73. • Ion pairs are formed when a cation and anion are
present in a solution of an ionizable substance, come
together to form a discrete chemical species.
• There are three distinct types of ion pairs, depending
on the extent of solvation of the two ions.
• For example, magnesium sulphate exists as both
contact and solvent-shared ion-pairs in seawater.
• Mg2+(aq) + SO42-(aq) ⇌ Mg(SO4)(aq)

74. • Ions of opposite charge naturally attracted to each
other by the electrostatic force.This is described by
coulomb's law:
• F=q1×q2÷€×r
• where F is the force of attraction,q1and q2 is
magnitude of electric charges,€ is the dielectric
constant of medium and r is the distance between
the ions.

75. • Ion association will increase as:
• the magnitude(s) of the electrical charges q1 and
q2 increases
• the magnitude of the dielectric constant
ε,decreases
• the size of ion decreases so that the distance r
between cation and anion decreases.

76. • https://youtu.be/c3g3maYegBk for videos
• https://g.co/kgs/Hmbd9i for theory
Reference