1. Lewis Diagrams and Covalent Bonds
Target 3-4a and Target 3-3

2. Target 3-4a / Target 3-3
3-4a. I can model covalent compounds by drawing Lewis diagrams.
3-3. I can write names and formulas of covalent compounds by interpreting and applying prefixes.

3. Bonding
Atoms join together to form molecules
‘join together’ = bond

4. Why do Atoms Bond?
All atoms can have up to 8 valence e- in their outer shells
(except H and He, which can have only two)
Atoms want outer shells to be full - it’s more stable

5. RECAP: What are valence electrons??
Valence electrons are the electrons in the OUTERMOST ENERGY LEVEL of an atom
We can find the number of ve’s by looking at the periodic table (find the group!)
Example: Cl = Group 17 = 7 ve

6. Cl Electron Dot Diagrams To draw ve’s in an electron dot diagram:
Write the element symbol
Imagine a box around it
Fill in the ve’s on the imaginary box lines (one per side, then double if necessary) Cl

7. How do Atoms Bond?
Some atoms form IONS - gain or lose electrons to make a full shell - positive and negative charges stick together
Some atoms SHARE their electrons with other atoms so they BOTH get full shells!

8. H Cl Sharing Electrons Here’s an example!
H has 1 v.e-, so it needs 1 more to get to 2
Cl has 7 v.e-, so it needs 1 more to get to 8 H
Unpaired e- Cl
Paired e-
Unpaired e-

9. H Cl Sharing Electrons H will share its e- with Cl
Cl will share its e- with H H Cl

10. H Cl Sharing Electrons H has a full shell with 2 e-
Cl has a full shell with 8 e- H Cl

11. H Cl Sharing Electrons H has a full shell with 2 e-
Cl has a full shell with 8 e-
*The line represents a single bond (1 pair of e’s) H Cl

12. How to draw Lewis Diagrams:
Draw out all atoms in formula – use electron dot diagrams
Arrange them around a central atom – the atom with the MOST unpaired electrons
Pair up the unpaired electrons to make bonds
Does every atom have a full valence level? If not, you may need to add double bonds!

13. How to draw example - H2O
1. Draw out atoms in formula: H O H

14. H O H How to draw example - H2O
2. Arrange them around a central atom (the one with the most unpaired electrons – O!) H O H

15. H O H How to draw example - H2O
3. Pair up the unpaired electrons to make bonds: H O H

16. H O H How to draw example - H2O
3. Pair up the unpaired electrons to make bonds: H O H

17. H O H How to draw example - H2O
4. Does every atom have a full valence level?
2e 8e (full) (full)
2e (full)
**Bonds count as 2 electrons for BOTH atoms!!** H O H

18. How to draw example - O2
1. Draw out atoms in formula, count e-:

19. How to draw example - O2
1. Draw out atoms in formula O O

20. O O How to draw example - O2
2. Arrange them around a central atom (the one with the most unpaired electrons): O O

21. O O How to draw example - O2
3. Pair up the unpaired electrons to make bonds O O

22. O O How to draw example - O2
4. Does every atom have a full valence shell? O O

23. O O How to draw example - O2
4. Does every atom have a full valence shell?
Each O only has 7 e-
5 (drawn) + 2 (bond) = 7 e- total O O
These e- are unpaired!!! NOOOOOOOOOO

24. How to draw example - O2
FIX IT BY MAKING A DOUBLE BOND O O

25. How to draw example - O2
FIX IT BY MAKING A DOUBLE BOND O O

26. How to draw example - O2
FIX IT BY MAKING A DOUBLE BOND O O

27. O O How to draw example - O2
4. Does every atom have a full valence shell?
YES!
Each O has 8 e-
4 (drawn) + 4 (bond) = 8 e- total O O

28. Naming Covalent Compounds
It is easy to find a formula based on a Lewis diagram and vice versa
We also want NAMES for our compounds
Write the name of each element (write them from left  right on the periodic table)
Change the name of the last element to end in “ide”
Add prefixes to tell the number of atoms for each element **do not use a prefix for the first element if there is just 1 atom

29. Naming Covalent Compounds - Prefixes
Number of Atoms
Prefix 1
Mono **use on 2nd element only 2
Di- 3
Tri- 4
Tetra- 5
Penta- 6
Hexa- 7
Hepta- 8
Octa- 9
Nona- 10
Deca-

30. Naming Covalent Compounds – Examples
C3H6 = 3 carbon, 6 hydrogen Tricarbon hexahydride
N2O5 = 2 nitrogen, 5 oxygen Dinitrogen pentoxide
CS2 = 1 carbon, 2 sulfur Carbon disulfide (remember – no prefix if the first element is 1)
Diphosphorous hexachloride phosphorous, 6 chlorine = P2Cl6
Carbon tetrafluoride carbon, 4 fluorine = CF4