1. March 20, 2018
Polarity
Bonding
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

2. Do Now (4 min) When you boil water, which is occurring?
March 20, 2018
Learning target: I can determine the polarity of compounds using lewis dot structures and electronegativity
Do Now: (Answer on your Do Now Sheet)
When you boil water, which is occurring?
The water molecules are breaking apart into H and O
The water molecules are separating into separate H2O molecules
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

3. What is a bond?
A bond can be thought of as a force that holds groups of two or more atoms together and makes them function as a unit
Example : water O
Bonds require energy to break
and release energy when made H H
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

4. Types of bonds
Ionic bonds - typically formed between metals and nonmetals
Covalent bonds - typically formed between nonmetals
Metallic bonds - formed between metals
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

5. Covalent Bonds Covalent Bonds exist between nonmetals bonded together
form when atoms of nonmetals share electrons
electrons can be shared equally or unequally
The unequal sharing results in polar molecules
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

6. Types of Bonds
Intramolecular bonds: Bonds that hold a molecule together (like holding the H to the O in H2O)
Intermolecular bonds: Bonds that hold two or more molecules together (like holding one water molecule to another)
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

7. Focus on Intermolecular Bonds
Intermolecular Bonds – also called intermolecular forces, or IMFs
We need to use Electronegativity
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

8. Electronegativity
Electronegativity values for each element are obtained by using the Periodic Table
What is the trend for EN on the periodic table?
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

9. How can we tell really tell which type of bond we have?
Electronegativity – how strongly an atom attracts electrons to itself
This tells us what type of bond we have:
Nonpolar Covalent, Polar Covalent or Ionic
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

10. Electronegativity
We take the difference between the electronegativity values to determine exactly what type of bond exists, in essence the polarity of the bond
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

11. Determining Bond Polarity
Look at the EN difference:
< 0.5: nonpolar covalent bond (equal sharing)
0.6 – 1.6: polar covalent bond (unequal sharing)
>1.7: ionic bond (transferring electrons)
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

12. Bond Polarity
Use your Reference Tables to determine the difference in electronegativity values and the type of bond for each of the following:
H-H
H-Cl
H-O
H-S
H-F
NaCl O2
KBr
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

13. Lewis Structures Tell ALL
When we draw CORRECT Lewis dot structures, we can decide whether molecules are symmetric or not…
Symmetric: all surrounding atoms are the same
Asymmetric: not all surrounding atoms are the same, there are lone pairs on the central atom
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

14. Lewis Structures Tell ALL
Let’s practice drawing Lewis dot structures:
NH3 NH4+ CO2 H2O
Which of the above are symmetric?
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

15. Molecular Polarity You solved bond polarity with EN values
You solved for the symmetry using Lewis dot structures
Now, let’s find the molecule polarity
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

16. Molecular Polarity Depends on 2 factors.
Type of bonds in the molecule (polar or nonpolar)
Arrangement of bonds or shape of molecule
(symmetric or asymmetric)
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

17. Diatomic Molecules Simplest case:
Bond Polarity and Molecular Polarity are identical
ex: H2 CO N2 HCl
Larger Molecules – Have to look at how the bonds are arranged.
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

18. For larger molecules, look at the kind & arrangement of bonds to determine overall polarity of molecule.
CH3Cl has 4 bonds.
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

19. Polarity of Molecules To be POLAR: Polar bonds Asymmetric shape
To be NONPOLAR:
Nonpolar bonds OR
- Polar bonds AND symmetric shape
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

20. Symmetric Molecules Contain at least one mirror plane. March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

21. Symmetric vs. Asymmetric
CO2 is nonpolar.
Can’t tell the ends apart.
H2O is bent.
Electron cloud is lopsided.
H2O is polar.
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

22. Polarity of CO2?
Draw an arrow along each bond pointing to the more electronegative atom.
If the arrows cancel out, the molecule is NONPOLAR.
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

23. Polarity of H2O?
The green arrows do not cancel out, so water is polar!
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

24. Symmetry of Larger Molecules
CF4 is fairly symmetric. Overall, it is nonpolar.
The arrows cancel out.
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

25. Molecular Polarity
If you know the shape, you can use the arrow technique to determine the polarity.
So how do you get the shape?
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

26. Practice! Use the structural formula to predict Molecular Polarity!
H  C  H  
March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

27. Practice CH4 C2H4 NO2+ H2S CH3Br March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

28. Homework Complete the Everyday chemistry for Homework March 20, 2018
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity

29. Exit ticket (3 min)
March 20, 2018
EXIT TICKET: Complete on a separate sheet of paper
Determine whether CS2 is polar based upon lewis dot structure and EN
Learning Target: I can determine the polarity of compounds using lewis dot structures and electronegativity