1. Dr. Fred Omega Garces Chemistry 100 Miramar College
6.04 Polarity of Molecules
Predicting Molecular Polarity
Dr. Fred Omega Garces
Chemistry 100
Miramar College

2. VSEPR Table: Revisited
Chemicals with Lone-pairs will always be polar.

3. Magnetic & Molecules Molecules and Magnets
Molecules possess magnet-like properties. Magnets have poles (+)-end (-) end. Molecules too can behave similarity to that of magnets with poles (dipole).
Magnets:
Magnet behavior - polar (with poles)
Non magnet behavior - nonpolar (without poles)
Molecules

4. Symmetry and Leverage: Tug of War and Polarity
The Charge distribution may cancel out (nonpolar) or there may be a net distortion (polar)
Analogy:
1. No one wins: nonpolar
2. One team wins: polar
3. a) no one wins: nonpolar
b) one team wins: polar
c) two team wins polar

5. Not all Covalent bonds are based on Mutual Sharing
Not all covalent bonds are made by bonding electrons being mutually shared between atoms
3. Because oxygen has more protons than hydrogen, it has a greater attraction for the bonded electron (it has a stronger electronegativity) this gives oxygen a  - charge and hydrogen a  + charge
4. This separation of partial charge results in the polar properties of water.
1. The oxygen atom is proceeding to form a bond with the Hydrogen atom
2. The oxygen atom and the hydrogen atom form bonds by sharing electrons

6. Electronegativity
Compounds: When atoms combine to form compounds, electrons can either transfer from one atom to another, partially transfer from one atom to another or the electrons can be mutually shared between atoms.
Transfer, partially transferred or equally shared: The behavior of the electrons is determined by the strength by which atoms attracts the bonding electrons.
Electronegativity. The degree of which an atom attracts an electron. The greediness of an atom for bonding electrons. Small atoms with the highest ionization energy have the highest Electronegativity.
Most Stingy Atoms near the north east corner of the periodic table are the most electronegative.
Degree of polarity is based on difference of EN, or D c

7. Unequal sharing of bonding electrons lead to polar bonds.
Electronegativity
When there is an unequal sharing of electrons between two atoms; the more stingy atom draws electrons bonded to itself.
Electronegativity - Ability of an atom to draw bonded e- on to itself.
If an atom is “stingy” for bonded electrons, then that atom is more electronegative that the atom it is bonded to.
Trend ?
Unequal sharing of bonding electrons lead to polar bonds.

8. Determining Molecular Polarity Flowchart (Details later)CO NO N2
ICl HI H2
How many central atoms?
None Dc
1 only
2 or more
Are there lone pairs
on central atom?
Are there lone pairs
on any central atom?
Yes No
Yes No
Polar*
Are all terminal atoms
the same element?
Polar*
Are all central atoms
the same element? No
Yes
Yes No
Polar*
Non-polar
Are all terminal atoms
the same element?
Polar No
Yes
Polarity depends
on symmetry
Non-polar
*This is true for everything that has up to 4 regions of electron density (i.e., what we’re studying in this class). It may not be true for other structures, such as an octahedron.

9. Dipoles and its mechanism
Recall the criteria for Covalent - Polar Covalent - Ionic Compounds Dc
Bond Dipoles: Cl-C-C-Cl
H-O-H
H-Cl
H-F
Molecules possessing net dipole moment are polar

10. Polar Bonds and Polar Molecules
Electron cloud distortion due to electronegative atom drawing electrons on to itself.
Polar Molecules
If the electron cloud is distorted over the entire molecule (i.e., winner in the tug-of-war) then molecule is polar.
Nonpolar molecule
If bonds are not polar or if polar bonds cancel each other (no winner in the tug-of-war), then molecule is non-polar.
(Polar bonds does not necessitate polar molecules)

11. Polar Molecules in the presence of a magnetic field
Molecules will align along a magnetic field based on their polar properties.
The H2 molecules shown on the left are not influenced by a magnetic field since H2 is a nonpolar chemical. On the other hand the HF molecule orientated themselves such that the the partially negative fluoride are orientated towards the positive charge in the magnetic field. This also applies to molecules with more than two element. In H2O, the molecule is polar and it orientates itself in the presence of a magnetic field. Note however that dichloroethyne is nonpolar and is not influenced by a magnetic field.

12. Water, a special polar molecule: More later
Water is a special molecule that is unique compared to other light weight molecule. Ordinarily, light weight molecule exist as a gas at temperatures above 0°C. Example are CH4, N2, O2, SO2, NH3. The special properties of water is due to its polar properties and its ability to stick among itself. The molecular mechanism by which water sticks to themselves is due to its polar nature and something called H-bonding. H-bonding will be covered more later in this chapter.
As a result of this mechanism, water is a liquid at room temp, has a lower density in its solid state, has a low vapor pressure among others.
Properties:
Density - low density
Surface tension - bugs walking on water
Capillary action - method of which trees drink
Specific Heat
Viscosity - high viscosity
Boiling point / melting point Higher than expected: Heat of fusion/Vaporization
Vapor pressure - low vapor pressure
Elaborate later in next section

13. Determining Molecular Polarity Flowchart (Details later)
How many central atoms?
None Dc
1 only
2 or more
HF(2.1, 4.0)
Binary Molecules
HBr(2.1, 2.8)
Are there lone pairs
on central atom?
Are there lone pairs
on any central atom?
FF(4.0, 4.0)
MgO(1.2, 3.5)
Yes No
Yes
FeS No
NaCl(0.9, 3.0)
Polar*
Are all terminal atoms
the same element?
CuS(1.9, 2.5)
Polar*
Are all central atoms
the same element? No
Yes
Yes No
Polar*
Non-polar
Are all terminal atoms
the same element?
Polar No
Yes
Polarity depends
on symmetry
Non-polar
*This is true for everything that has up to 4 regions of electron density (i.e., what we’re studying in this class). It may not be true for other structures, such as an octahedron.
CO(2.5, 3.5)
HH(2.1, 2.1)
NO(3.0,3.5)

14. Determining Molecular Polarity Flowchart (Details later)
How many central atoms?
None Dc
Binary Molecules
NaCl
CuS
FeS
MgO HF NO HH FF
HBr CO

15. Determining Molecular Polarity FlowchartCO
H2O2
F2CCH2
H3CCH3
H3NBH3 O2
CO2 CH2F2 O3
NCCH3
NCCl
How many central atoms?
None Dc
CO or O2
1 only
2 or more
Are there lone pairs
on central atom?
Are there lone pairs
on any central atom?
Yes No
Yes No
Polar*
Are all terminal atoms
the same element?
Polar*
Are all central atoms
the same element? O3
H2O2 No
Yes
Yes No
Polar*
Non-polar
Are all terminal atoms
the same element?
Polar
CO2
H3NBH3
CH2F2
:NΞC-Cl No
Yes
Polarity depends
on symmetry
Non-polar
H3CCH3
*This is true for everything that has up to 4 regions of electron density (i.e., what we’re studying in this class). It may not be true for other structures, such as an octahedron.
F2CCH2
:NΞC-CH3

16. Determining Molecular PolarityNP
How many central atoms?
Are there lone pairs
on central atom?
on any central atom?
1 only
2 or more
Polar*
Are all terminal atoms
the same element?
Yes No
Non-polar
Are all central atoms
Polar
Polarity depends
on symmetry
NºC-CH3
C O

17. Determining Molecular PolarityNP
How many central atoms?
Are there lone pairs
on central atom?
on any central atom?
1 only
2 or more
Polar*
Are all terminal atoms
the same element?
Yes No
Non-polar
Are all central atoms
Polar
Polarity depends
on symmetry
Nº C-CH3
C O

18. Molecular Polarity: Examples
Linear BeH2 (electron deficient molecule)
Trigonal BH3 (electron deficient molecule)
Tetrahedral CH4
Pyramidal NH3
Bent H2O Tetra-Bent SO2 Trig-Bent
O3 NO3- CS2 H2O2
C3H4 CH3Cl SiO2 COCl2
SO3 OF2 C2H2 H2CO
PF3 CI4 HCN NF3
Assignment on VSEPR and Polarity Determination

19. Summary Key to determine Polarity of molecule. • Lewis Structure
Atoms with different EN - Polar.
• VSEPR Structure
Symmetry (or distortion) of e- cloud; (tug-of-war).
Central atom (A) has lone pair of electrons.
• Polarity
Net distortion of the electron Cloud.