1. Bond Types

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 (write on Periodic Table)
Why don’t the noble gases have a value?
They don’t attract electrons!

7. Ionic Bonds
If the electronegativity difference is greater than 2.0, one atom will pull the electron completely away from other atom.
The electrons are NOT shared.
An Ionic Bond is formed as + and – attract.
Electronegativity of Na is 0.9; Cl is 3.0.
3.0 – 0.9 = 2.1; difference > 2.0, so…Ionic!

8. 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 between 0.4 – 2.0, one side of the bond becomes slightly more negative and the other side becomes slightly more positive.
This is a Polar Covalent Bond.

9. Polar Covalent Bonds ∂- ∂+Cl H ∂+ ∂-
Slightly
The electronegativity of H is 2.1; Cl is 3.0.
3.0 – 2.1 = 0.9; difference is b/w 0.4 – 2.0, so…Polar Covalent!

10. Polar Covalent Bonds The electronegativity of O is 3.5; H is 2.1.
3.5 – 2.1 = 1.4
Difference is b/w 0.4 – 2.0, so… Polar Covalent!

11. Nonpolar Covalent Bonds
When the atoms have equal pull, causing the electrons to be equally shared, the bond is Nonpolar Covalent.
Neither side of the bond is even slightly positive or negative.
The electronegativity difference is b/w 0.0 – 0.4.
This is the type of bond that occurs between 2 atoms of the same element. (H2, O2, Cl2, etc.)

12. Nonpolar Covalent Bonds
The electronegativity of H is 2.1.
2.1 – 2.1 = 0
The difference is b/w 0.0 – 0.4, so…Nonpolar!

13. 3 Different Types of Bonds

14. Attractions Between Molecules Van der Waals Forces
Weaker than either the ionic or covalent bonds that form between atoms in a compound.
Responsible for determining whether a compound is a liquid, gas, or solid
3 basic types from weakest to strongest
(London) Dispersion forces
Dipole interaction
Hydrogen bonding

15. London Dispersion Forces
Weakest of all molecular attractions
Caused by the motion of electrons producing a temporary polarity.
Strength of dispersion forces generally increases as # of electrons in the molecule increases.
All molecules have these weak attractions.

16. London Dispersion Forces

17. Dipole Interaction
Occurs when polar molecules are attracted to one another

18. Hydrogen Bonds
Occurs b/w molecules in which H is covalently bonded to either O, N, or F, which are very electronegative
Causes very polar molecules that are strongly attracted to each other
Still only has about 5% of the strength of a covalent bond

19. Hydrogen Bonds + Very Important!! Reason ice is less dense than water
Reason for the relatively high b.p. of water
Responsible for the double helix of the DNA molecule O H +
2 lone pairs

20. 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?

21. Nonpolar or Polar Molecules
Draw the Lewis Structure.
If the central atom has any unshared pairs, the molecule is polar.

22. 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.

23. Nonpolar or Polar Molecules
H2O
CO2
HCN
CH3Cl
Polar
Nonpolar
HCl
Polar
Polar N2
Nonpolar
Polar

24. 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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