1. Chapter 9 Notes – Part II
Mr Nelson 2009

2. Warm Up – ionic, molecular or acid
HBr Chlorous Acid
FeS Copper(I) fluoride
PBr5 dinitrogen dioxide
K2SO4 nitrogen monoxide
CCl4 hydroiodic acid
HNO3 potassium nitrate
LiCl phosphoric acid

3. Resonance
Draw the Lewis dot structure for ozone, O3.

4. Resonance
But this is at odds with the true, observed structure of ozone, in which…
…both O-O bonds are the same length.
…both O-O bonds have the same strength

5. One Lewis structure cannot accurately depict a molecule like ozone.
We use multiple structures, resonance structures, to describe the molecule.

6. Resonance Example
HCO2-

7. Electrons that form the second C-O bond in the double bonds below do not always sit between that C and that O
They move among the two oxygens and the carbon.

8. Exceptions to the Octet Rule
Three situations with exceptions to the octet rule:
When Ions or molecules have:
an odd number of electrons
less than an octet (B & Al)
more than eight valence electrons (an expanded octet)

9. Exceptions!
Boron and Aluminum are okay with only 6 e- around them
BF3

10. More Than an Octet
PCl5 can only exist is if phosphorus has 10 electrons around it.
Presumably d orbitals in these atoms participate in bonding.

11. Different Bond Types Ionic (extremely polar) Covalent
Electrons are transferred
Covalent
Polar – uneven sharing of electrons
Nonpolar – even sharing of electrons

12. Nonpolar Covalent Bonds

13. Polar Covalent Bonds

14. Ionic Bonds

15. Electronegativity
Electronegativity is the ability of atoms in a molecule to attract electrons to themselves.
On the PT, EN increases:
…from left to right across a row.
EN decreases
…from the top to bottom of a group (column).

16. Bond Properties and Electronegativity

17. Bond properties and electronegativity
Any bond can be classified by subtracting the EN of the 2 elements involved
High differences in electronegativity (1.7 – 4) make the bond IONIC
Low differences (0-1.7) make the bond COVALENT:
Polar covalent – 0.4 – 1.7
Nonpolar Covalent – 0 – 0.4

18. Polar Covalent Bonds
Electrons are not always shared equally in compounds.
Oxygen pulls harder on the electrons it shares with hydrogen than hydrogen does.
Oxygen’s end of the molecule has more electron density than the hydrogen end.

19. Nonpolar, polar, and ionic bonds
(a) – a nonpolar covalent bond
(b) – a polar covalent bond
(c) – an ionic bond

20. Polar Covalent Bonds
When two atoms share electrons unequally, a bond dipole results.

21. Polar Covalent Bonds
The greater the difference in electronegativity, the more polar is the bond.