1. Electrons in Atoms Unit
Bohr Model, Lewis Dot for Elements, Valence Electrons

2. Like our solar system … Nucleus is like our sun
Electrons are like our planets
Electrons on energy levels!
Ask what is our nucleus made up of? Then click for nucleus picture
Go to electrons are like planets
Then say where do our electrons live at in our atom? The energy levels (click for the rest of the Bohr Model)

3. How do we draw a Bohr Model?
Model Only Really works for Hydrogen
How do we draw a Bohr Model?
1.) Draw a nucleus
2.) Determine how many electrons you need
3.) Draw energy levels around nucleus
Each energy level can only hold so many electrons
1st = 2 e-
2nd = 8 e-
3rd = 8 e-
4th and up = 2 e-
4.) Place electrons on each energy level until you reach the amount of electrons you need (refer to step #2)
How many e- on
1st = ____
2nd = ____
3rd = ____
4th = ____
Total = ____ Ca 20
40.078

4. Draw the Bohr Model for: Sodium Oxygen
1.) Draw a nucleus
2.) Determine how many electrons you need
3.) Draw energy levels around nucleus
Each energy level can only hold so many electrons
1st = 2 e-
2nd = 8 e-
3rd = 8 e-
4th and up = 2 e-
4.) Place electrons on each energy level until you reach the amount of electrons you need (#2)
Draw the Bohr Model for:
Sodium Oxygen

5. Identify the element from its Bohr Model
How many e- on
1st = ____
2nd = ____
3rd = ____
4th = ____
Total = ____
Proton
Neutron
Electron

6. Identify the element from its Bohr Model
How many e- on
1st = ____
2nd = ____
3rd = ____
4th = ____
Total = ____
Proton
Neutron
Electron

7. Valence Electrons
The outermost electrons on the highest occupied energy level of an element

8. How do we find the number of valence electrons?
Bohr diagram
Periodic table
BEST CHEAT SHEET EVER! + -
How many valence electrons are present in the last energy level of Calcium?

9. 1 2 3 4 5 6 7 8

10. How many valence electrons are in . . .
Cl __________
Ba __________
Ne __________
He __________

11. X • • • • • • • • Lewis Dot Structures
System of arranging dots to represent the valence electrons
G. N. Lewis developed this system
Dots represent the valence electrons
Max of 8 around the symbol
First two together
Rest go “counter-clockwise” • • X • • • • • •

12. Example: How many valence electrons does phosphorous have?
Write the Lewis dot structure for phosphorous

13. Practice Mg S Cl Rb Si Ar

14. IONS – charged atom
Elements will gain or lose electrons to achieve an OCTET.
This means they want to have 8 valence electrons
Known as the OCTET RULE

15. Cation – K becomes K+ B becomes B3+ Positive ion
Loses electrons to become more positive
Why?
Easier to lose 1, 2 or 3 e- than it is to gain 5, 6 or 7 e-
K becomes K+
B becomes B3+

16. Anion Cl becomes Cl- O becomes O2- Negative ion
Gains electrons to become more negative
Why?
Easier to gain 1, 2 or 3 electrons than to lose 5, 6, or 7 e-
Cl becomes Cl-
O becomes O2-

18. Draw the Lewis Dot Structure for these ions:
Na+
O2-
Mg2+

19. Draw the Lewis Dot Structure for these ions:
Cl-
Al3+ F-