Polarity of molecule to its properties

1. POLARITY OF A MOLECULE
TO ITS PROPERTIES

2. Solubility is defined as the ability of a solid
substance to be dissolved in a given amount of
solvent while miscibility is the ability of the two
liquids to combine or mix in all proportions,
creating a homogenous mixture.
The general rule to remember about the
solubility and miscibility of molecular
compounds can be summarized in a phrase,
“like dissolves like” or “like mixes with like”.
Example:
benzene (C6H6) and chloroform (CHCl3) – both
nonpolar
water (H O) and vinegar (CH COOH) – both

3. Intramolecular forces of attraction- the attractive force within the
molecule that keep the molecule together for example, the bonds
between the atoms together. Example: Covalent bond in H20 and
polar Ionic bond in NaCl
Intermolecular forces of attraction (IMFA)- are the attractions between
molecules which many of the physical properties of a substance.
There are several types of IMFA and below they are arranged from
STRONGEST to WEAKEST.
Ion-dipole → H-bonding→ dipole-dipole→dipole-induced dipole→
London forces of attraction
The strength of IMFA greatly affects the physical properties of
substances such as boiling point, melting point, vapor pressure,
surface tension, etc.

5. Both are
polar
molecule

6. Polar molecules Nonpolar molecules
• IMFA type: H-bonding
and dipole-dipole
• IMFA type: London
dispersion
• exist as solids or liquids
at room temperature
• exist as gases at room
temperature
• High boiling point • Low boiling point
• High melting point • Low melting point
• High surface tension • Low surface tension
• Low vapor pressure • High vapor pressure
• Low volatility • High volatility
• Soluble in water • Insoluble in water
Table 2. General Properties of polar and nonpolar molecules

7. TABLE 1. SUMMARY OF TYPES OF INTERMOLECULAR
FORCES OF ATTRACTION (IMFA)
Type of IMFA Interacting Substances Examples
Ion-dipole Ion (cation or anion) and
a polar molecule
NaCl dissolved in H2O;
Ca2+ and PCl3
Hydrogen bonding Polar molecules containing H
chemically bonded to a small
and
highly electronegative
nonmetal atom such as
N,
O, and F
H2O, NH3, CH3OH
Dipole –dipole Polar molecules CH3F and H2S; HCl;
Dipole-induced dipole Polar and nonpolar
molecules
HI and CH4
London forces All substances and solely O2, N2, He gas, Br2

8. PHYSICAL PROPERTIES OF
SUBSTANCES:
Boiling point: temperature at which the vapor pressure and
atmospheric pressure of a liquid substance are equal.
Melting point: temperature at which solid becomes liquid. At
this point, the solid and liquid phases exist in equilibrium.
Surface tension: energy needed to increase the surface area by
a unit amount;
Viscosity: the resistance of the liquid to flow
Vapor pressure: pressure exerted by a substance in its gaseous
state.
Volatility: measures the rate at which a substance vaporizes
(changes from liquid to gas)

9. Polarity is a physical property of
compounds which relates other physical
properties such as melting and boiling
points, solubility, and intermolecular
interactions between molecules.
In a few cases, a molecule may have polar
bonds, but in a symmetrical arrangement
which then gives rise to a non-polar
molecule like carbon dioxide. (3.5-2.5=
1.0)

10. In the simplest sense, boiling point, melting
point, viscosity and surface tension increase as
the strength of intermolecular forces increases.
On the other hand, vapor pressure and volatility
decrease with increasing strength of IMFA.
London dispersion forces increase as the
molecular mass of a substance increases.

11. Polar molecules are
asymmetric, either
containing lone pairs
of electrons on a
central atom or
having atoms with
different electro
negativities bonded.

12. PROPERTIES DUE TO POLARITY
Polarity is a separation of electric charge leading to a molecule
or its chemical groups having an electric dipole moment, with
a negative and positive charged end.
Molecular polarity controls or determines the strength and
types of intermolecular forces of attraction between molecules.
The easiest properties to understand regarding polarity is
melting and boiling points. The more polar a molecule is, the
greater its attraction to other molecules like it. This means
that they will stick or attract together tightly even if given a lot
of energy. Ionic molecules are generally solid at room
temperature. As a matter of fact, it can take a lot of energy to
melt many of them (>1000°F). Example is NaCl.

13. -Polar molecules like water are liquid at room
temperature. They have a strong attraction to each
other, but not as strong as ions. Molecules that are
nonpolar do not have the attraction. The only thing
that keeps them together is their size.
-Larger nonpolar molecules like gasoline can be a
liquid at room temperatures but become a gas very
easily. Most small. nonpolar molecules (CH4) are
gases for a very long period of time. N2 becomes a
liquid at -196°C (-320°F).
-the more polar the molecule and the greater its
solubility in polar solvents like water and the higher

14. Polar molecules interact through
dipole–dipole intermolecular
forces and hydrogen bonds.
Polarity causes a number of
physical properties including
surface tension, solubility, and
melting and boiling points.

15. Gasoline is a non-polar and more soluble in nonpolar
solvents like hexane and it will have relatively low boiling
and melting points.
The polarity of a molecule has a strong effect on its physical
properties. Molecules which are more polar have stronger
intermolecular forces between them and have higher boiling
points as well as other different physical properties.
Polarity refers to the physical properties of compounds such
as boiling point, melting points, surface tension and their
solubility. The polarity of bonds is caused due to the
interaction of the bonds between molecules and atoms with
different electro negativities.
The Non-polar molecules aren't attracted to each other as
much as in polar molecules, these molecules are much less
likely to have high surface tension.

16. WHAT DO WE CALL COMPOUNDS
THAT ARE COVALENT? MOLECULES

18. PROPERTIES OF MOLECULES
Covalent Bonds-

19. All molecules are composed of Non Metals,
with some Organic molecules having slight
traces of metals. Ionic compounds always
have metal elements.

20. PROPERTIES OF MOLECULES
Covalent bonds-

21. PROPERTIES OF MOLECULES/
COVALENT BONDS

22. PROPERTIES OF MOLECULE

23. Q1. How does polarity affect physical properties?
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Q2. Explain why nonpolar molecules usually have much lower surface tension than polar
ones.
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Q3. Briefly explain why water is considered as the universal solvent.
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Q4. How can you determine if the polarity (polar and nonpolar molecule) is symmetric or
asymmetric?
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24. Substance
Boiling point
(0C)
Melting point
(0C)
Helium gas,
He
-269 -272
Methane, CH4 -162 -184
H2O 100 0
Ethanol,
C2H5OH
78 -117
•Using the concept of IMFA, account for the difference in boiling
point and melting point of the following molecular substances:

25. Direction: Label each of the following as polar or nonpolar molecule
and explain why.
Sample Molecules Polarity Explanation
1. Propane, C3H8
2. Water, H2O
3. Methanol, CH3OH
4. Oxygen, O2
5. Hydrogen cyanide,
HCN