1. Or how to be a greedy little atom
POLAR COVALENT BONDS
Or how to be a greedy little atom

2. Electronegitivity
Electronegitivity: The ability of an atom in a molecule to attract electrons. (Table on pg. 320)

3. The big reveal… The electronegativity of a
bond controls the type of bond atoms form:
Electronegativity difference
between bonding atoms: Bond Type:
Zero Covalent
Small to intermediate Polar covalent
Large Ionic

4. Polar covalent bonds
Covalent bonds share electrons, but not always equally.

5. Polar covalent bonds
Electrons in a bond will spend more time near the atom with the highest electronegativity.
This causes partial charges

6. Practice
Which atoms in the following bonds are the most electronegative?
HCl
FBr
H2­O
CCl4

7. Practice
Now draw the following molecules in VSEPR model form with partial charges.
HCl
FBr
H2­O
CCl4

8. End Day 1
HW: Molecular Polarity Worksheet

10. Polar Covalent Bonds
These are called Polar Covalent Bonds. Covalent because they are sharing electrons. Polar, because they have ends (positive and negative).
A more polar has a greater difference between the electronegativity values of the two atoms making the bond.
Arrange the following bonds in order of increasing polarity:
F-H, N-H, H-H, O-H, B-H

11. Arrange the following bonds in order of increasing polarity:
F-H, N-H, H-H, O-H, B-H

12. Polar Covalent Bonds Day 2
Dipole moments
Due to different electronegativity values, covalent bonds do not always share electrons equally. This causes certain atoms in a polar covalent molecule to be slightly negative and others to be slightly positive.

13. Dipole Moment Examples
 Write the Lewis dot structure for HF, then the shape, and finally label the charges.
Notice one side of the atom is more positive while another side is more negative.
To show one side is more “+” than the other we are going to draw an arrow from the center of positive charge to the center of negative charge. We call this the Dipole Moment.

14. Dipole Moment Examples
Example 2: H2O
Write the Lewis dot structure.
Now draw the VSEPR Shape. Make sure to write the O and H’s where they are located.
Now label each atom in the VSEPR shape with its charge.
Draw the dipole moment.

15. Practice
Note: If there is not one side more positive or negative than the other, there is no dipole moment. H2
FCl
SF2
CH2Cl2

16. Homework: Part 1: Add the dipole moment to last nights HW
Read
Part 2: Answer Q/P: #5-11, 13

17. Effect on Physical Properties:
The more polar a bond, the bigger difference in charge.
The more difference the charge, the greater attraction to other molecules around it.
 IMFA: Intermolecular Forces of Attraction (or how attracted are the molecules are to each other).

18. Bond Type: Charges: Strength of IMFA
Ionic +, - Strong
Polar Covalent slightly +, slightly – Medium
Covalent none weak/none

19. Effect on Physical Properties
These charges cause the different molecules to be attracted to each other.
In Ionic (strong): this forms the crystal lattice
In covalent (weak/none): London dispersion (tomorrow)
In polar covalent: (draw picture on board)
The opposite side (+/-) of polar covalent molecule cause them to be strongly attracted to each other. The more polar = the stronger the attraction. This causes a higher boiling point.

20. Effect on Physical Properties
Difference in Electronegativity
Examples
Type of Bond
Charge
Strength of IMFA
(attraction)
Boiling Point
None
N2, O2, H2
Covalent
Low
Very Low
Medium/varies
H2O, CO2 , CH4
Polar Covalent
Partial +/-
Medium
High
NaCl, MgF2
Ionic
Full +/-
Solubility:
Polar covalent or Ionic compounds can only dissolve into polar covalent liquids.
Covalent molecules can only dissolve in non-polar liquids (Covalent liquids).

21. Homework
Polarity Worksheet

23. Effect on Physical Properties
Difference in Electronegativity
Examples
Type of Bond
Charge
Strength of IMFA
Type of IMFA
Boiling Point
None
N2, O2, H2
Covalent
Low
London Dispersion
Very Low
Medium/varies
H2O, CO2 , CH4
Polar Covalent
Partial +/-
Medium
Dipole-Dipole,
Hydrogen Bonds
High
NaCl, MgF2
Ionic
Full +/-
Ionic Bonds