1. ELECTRON DOT FORMULAS—HOW DO THEY WORK?
(also known as Lewis dot structures)

2. THE “DOT” 1) Represents an electron
2) Specifically valence electrons (electrons in the outermost shell)

3. #1.
Cs C I

4. #2.
S Ca B
Guess: #3
Sr Cl Xe

5. Guess: #4.
O Ba N
Guess: #5
Kr Mg P

6. X What are the rules? 1) Number of dots = last digit of group #
2) Order of dots:
3) Why this order?
 first 2 are “s” electrons; next 6 are “p” electrons: 1 2 X 8 3 5 6 7 4

7. Guess: #6.
F Al Si
Guess: #7
Ar Be Na

8. OK, so you think you have it? Try these: Guess#8
Cl- Br- S2- - - 2-
Cl Br S

9. Just one more: Guess #9
O2- N3- Si4+ 2- 3- 4+
O N Si

10. What are the rules for ions?
1) Add or subtract the appropriate number of electrons
2) Place brackets around the Lewis dot structure
3) Write ion’s charge to the upper right hand corner

11. Octet Rule Notice there’s a trend for forming ions
The octet rule states that atoms will form ions by gaining or losing electrons so they will have a “full” valence shell of 8 (an “octet” of) electrons just like a noble gas
Exception: The duet rule is for hydrogen and helium—they obtain a full shell of 2 (a duet of) electrons