1. CHEM 121 Chapter 4

2. Ionic v. Covalent Substances
Ionic substances:
Ionic bonds:
Covalent substances:
Covalent bonds: - +

3. Covalent Bonds Form when atoms share electrons to form molecules
Usually between nonmetal and nonmetal
Atoms with….

4. Covalent Bonding H + H H H F + F F F

5. More Covalent Compounds+ H C + 4 H
Carbon atom:

6. Another Covalent Compound+ H N + 3 H
Nitrogen atom:

7. One more Covalent Compound+ H O + 2 H
Oxygen atom:

8. Lewis Dot Structure Hints
Draw only the ____________ electrons
Carbon group elements want ____________
Nitrogen group elements want ___________
and…
Oxygen group elements want ____________

9. Drawing Lewis Dot Structures
Count the total number of valence electrons
Arrange atoms so that at least one bond connects them
How many electrons are left?
These are lone pairs!

10. 3-minute review
Draw the Lewis Structures for each of the following covalent compounds:
CH3Cl
PH3
H2O2

11. Lewis Dot Structures for Ions
Polyatomic ions are ________________ bonded
When counting valence e-, include _____________
How many valence e- total in each of the following?
NO3-
SO42-

12. 3-minute review
How many valence electrons should be used to draw the Lewis Structure of acetate (C2H3O2-)?

13. Multiple Bonds O + C + O N + N

14. 3-minute review
Draw the Lewis Structures for each of the following covalent molecules: C2F6 C2F4 C2F2

15. Resonance Structures Molecules with more than one Lewis Structure O3
Usually involves swapping double bond e- with lone pair e- or other double bond e-
True structure is a _______________ O3

16. 3-minute review
Draw 2 resonance structures for the nitrate ion: NO3-

17. Exceptions to the Octet Rule
Hydrogen
Group 3A Elements
Third Row (and later) Elements

18. Examples: PCl3 and PCl5

19. Shapes of Molecules VSEPR: Minimize e- repulsion
e- groups pushed as far apart as possible
Electron groups:
Note: double, triple bonds count as ONE group

20. Basic Molecular Shapes
2 electron groups
3 electron groups

21. Basic Molecular Shapes: 4 electron groups
bent

22. Electronegativity
Electronegativity:
(EN)

23. Electronegativity & Bond Type
________________________ tells us whether a bond is more ionic or more covalent
Ionic bond:
Covalent bond:
Some difference in electronegativity:
No difference in electronegativity:
Polar bonds create a

24. Polarity of Molecules O H H-H F-F H-F Polar bond:
difference in electronegativities of bonded atoms
H-H
F-F
H-F O H

25. Polarity of Molecules C H Add polar bonds (head to tail)
Molecules with polar bonds may not be polar overall!

26. Covalent Compounds Combination of two different elements
Rules for Naming
______________________ element first;
______________________ element is second.
Second element: “root”-ide
Add Greek numerical prefixes

27. Naming Covalent Compounds
Example: CS2
Which element is less EN?
Second element is root-ide
Add prefix

28. Naming Covalent Compounds
Example: N2O
Which element is less EN?
Second element is root-ide
Add prefix

29. 3-minute practice Write the name for the following compounds: CF4 P2O5
SCl6

30. Acetaminophen Draw in lone pairs.
How many single bonds are in this molecule?
How many double bonds?
Are some bonds nonpolar?
Are some bonds more polar?
(Assume C and H have similar electronegativities.)