1. Link to Ionic Bonds
Link to NaCl

2. Link to MgCl2

3. Link to Li2O

4. Link to AlBr3

5. Looking for Patterns in Covalent Lewis Dot Structures

6. Covalent Lewis Dot Structure Notation
= nonbonding e- ; represents 1 e-; belong to only one atom Use to represent bonding pair of e- = e- e- = single bond (1 shared e- pair). Each dash represents 1 pair or 2 electrons. = e- e- = double bond (2 shared e-pairs) or 4 e- e- e- = e – e- e- = triple bond (3 shared e- pairs) or 6 e- e- e- e-
Link to Notes

7. Why do atoms form chemical bonds?
Lowest Energy Arrangement = Completely Filled Valence Electron Level
Atoms gain, lose or SHARE valence electrons in order to obtain a completely filled valence electron level.
First energy level: Filled = 1s2
All other energy levels = ns2np6 ↑↓
DUET RULE
OCTET RULE ↑↓ ↑↓ ↑↓ ↑↓

8. For each group of elements:
How many valence electrons do atoms in this group have? (Recall group # = # of valence e-)
How many bonds ( ) is each atom making?
How many nonbonding electrons (dots) does each atom have around it?
How many total valence electrons does the atom have in the final bonded structure?

9. H H H F H Cl H Br H H C H H N H H O H H H H2 HF HCl HBr H2O NH3 CH4
What patterns do you notice about #’s of bonds ( ) and nonbonding electrons (dots) and total valence e- on H?
H HF HCl HBr
H2O NH CH4 H H H F H Cl H Br H H C H H N H H O H H H

11. Duet Rule
Hydrogen always makes 1 covalent bond with no nonbonding electrons (dots) in order to fill the first energy level. H H H H H H H F H F

12. Group 7, Family 17 Halogen
ns2np5 F Cl Br I

13. O O O F2 Cl2 Br2 I2 HF HCl HBr HI H H H H OF2 OCl2 OBr2
What patterns do you notice about the # of bonds ( - ) and number of dots ( ∙ ) for F, Cl, Br and I?
F Cl Br I2
HF HCl HBr HI
H H H H
OF OCl OBr2 O O O

14. Octet Rule
Each F, Cl, Br or I atom starts with 7 valence electron and forms 1 bond (2e-) with 3 nonbonding pairs (6e-) to end up with 8 valence electrons:
F F F F x

15. Group 6 or Family 16 Elements

16. Group 6 Elements: O, S, Se H O H H S H H Se H H C O H H H O H C H S Se

17. Octet Rule
Each O, S, or Se atom starts with 6 valence electron and forms typically forms 2 bonds and 2 nonbonding pairs to end up with 8 valence electrons:
O O O O

18. Group 5, Family 15: N, P, As,

19. Group 5: N, P, As H N H H H As P H H H H H N N H N N H

20. Octet Rule
Each N, P, or Sb atom starts with 5 valence electrons and typically forms 3 bonds with 1 nonbonding pair to end up with 8 valence electrons: N N N N

21. Group 4, Family 14: C, Si,

22. Group 4, Family 14: C, Si

23. Octet Rule
Each C, or Si atom starts with 4 valence electrons and typically forms 4 bonds with 0 nonbonding pairs to end up with 8 valence electrons: O O C O C O

24. For each pattern, identify the element that could represent X
Choices: A) H B) F C) C D) N E) O
E) O
1) X
A) H
2) X
D) N
3) X
4) X
C) C
B) F
5) X

25. In hydroxide -1 ion, why does O make 1 bond instead of the usual 2?
Ans: -1 charge means O has gained 1 valence e- and acts like an atom with 7 valence e- instead of an atom with 6 valence e-.

26. In ammonium + ion, why does N make 4 bonds here instead of the usual 3?
Ans: + charge means N has lost 1 valence e- and acts like an atom with 4 valence e- instead of an atom with 5 valence e-.

27. Link to Notes

28. Draw the Lewis Dot Structure for CH2Cl2
Step #1: Determine Central Atom
Formula Method: Single atom in formula =
# of Bonds Method:
Step #2: Connect all atoms with single bonds coming off central atom: C
C =4 bonds, H =1, Cl =1 H Cl C Cl H

29. Draw the Lewis Dot Structure for CH2Cl2
3) Arrange dots so that each atom has filled outer energy level (Duet Rule for H, Octet Rule for Cl) H Cl C Cl H