1. Bond Types / Polarity

2. Chemistry Joke
Q: What do you pay a policeman who works security for a chemistry night class?
A: Copper Nitrate!

3. Let’s Look At 3 Types of Bonds
Ionic
Polar Covalent (Molecular)
Nonpolar Covalent (Molecular)

4. Remember Electronegativity?
The tendency for an atom to attract electrons to itself in a bond
The higher the value, the better it is at attracting electrons.
The difference in the electronegativity values determines what type of bond will be formed.

5. Electronegativity
Electronegativity is a scale from 0.7 (Cs) to 4.0 (F).
Electronegativity generally increases across a period and decreases down a group.

6. Electronegativity Values (on back of Periodic Table)
Why don’t the noble gases have a value?
They don’t attract electrons!

7. Ionic Bonds
If the electronegativity difference is great enough, one atom will pull the electron completely away from other atom—the electrons are NOT shared.
For example, electronegativity of Na is 0.9; Cl is 3.0.
This difference is very great, so the electrons are TRANSFERRED, forming ions.
Positive and negative charges attract creating an ionic bond.

8. Ionic Bonds

9. Polar Covalent Bonds Covalent bonds share electrons
The shared pairs are pulled, similar to a tug-of-war, between the nuclei of the atoms sharing the electrons.
If the electronegativity difference is large enough, one side of the bond becomes slightly more negative and the other side becomes slightly more positive.
This is a Polar Covalent Bond.

10. Polar Covalent Bonds Cl H ∂+ ∂-
Slightly

11. Polar Covalent Bonds The electronegativity of O is 3.5; H is 2.1.
These values are different, but not large enough for ions to form, so the bond is polar covalent.
The electrons are shared unequally.

12. Polar Covalent Bonds
For example, in a bond between H and Cl, This can be shown in 2 ways.
The symbol, δ, is a lowercase Greek letter delta, and it means here that there is a slight charge.
The + side of the arrow is the positive side.

14. Nonpolar Covalent Bonds
When the atoms have similar (or identical) electronegativity), the electrons are equally shared, and the bond is Nonpolar Covalent.
Neither side of the bond is even slightly positive or negative.
This is the type of bond that occurs between 2 atoms of the same element. (H2, O2, Cl2, etc.)

15. Nonpolar Covalent Bonds
The electronegativity of H is 2.1.
In an H2 molecule, there is NO difference in electronegativity, so the bond is nonpolar.

16. 3 Different Types of Bonds

17. Nonpolar or Polar Molecules
We now know how to determine if the bond b/w atom and atom in a compound is polar or nonpolar.
But…what about the whole molecule?
Sometimes polar bonds are positioned so that their polarity cancels.

18. Nonpolar or Polar Molecules
How can you tell?
Draw the Lewis Structure.
If the central atom has any unshared pairs, the molecule is polar.

19. Nonpolar or Polar Molecules
If there are no unshared pairs on the central atom, look at the atoms around the central atom.
If they are all the same, the molecule is nonpolar.
If any one of them is different, the molecule is polar.
In a 2-atom molecule, if the bond between the 2 atoms is polar then the whole molecule is polar.

20. Nonpolar or Polar Molecules
Lone pairs of electrons on O
No lone pairs on C; two of the same type of atoms bonded to C
H and Cl are two different atoms bonded together
No lone pairs on C; two different types of atoms bonded to C
Two identical atoms bonded together
One of the atoms bonded to C is different
H2O
CO2
HCN
CH3Cl
Polar
Nonpolar
HCl
Polar
Polar N2
Nonpolar
Polar

21. Q: How do we know that Chuck Norris is not a chemist?
Chemistry Joke
Q: How do we know that Chuck Norris is not a chemist?
A: The only element he knows is the “element” of surprise!
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