1. Bohr Models and Lewis Dot Diagrams

2. Niels Bohr

3. Bohr Models…
Niels Bohr explained the structure of the atom in his “Bohr models”. His model of the atom resembles a solar system. He came up with this model in Here is a typical Bohr model, what can you figure out from it?

4. Around the nucleus, it shows the electrons in shells or clouds
Bohr models show the nucleus in the center with the # of Protons (p) and Neutrons (n) in it
Around the nucleus, it shows
the electrons in shells or clouds
Each shell or cloud can only hold a
certain # of electrons and then
it is full.
Draw this in your notebook. Identify the number of protons, neutrons and electrons.
Protons: ___
Neutrons: ___
Electrons: ___

5. How many e- can each CLOUD hold?
1st cloud can hold 2 e-
2nd cloud can hold 8 e-
3rd cloud can hold 18 e-
4th cloud can hold 32 e-
5th cloud can hold 32 e-
6th cloud can hold 18 e-
7th cloud can hold 8 e-

6. How many do I need to know for the test?
1st cloud can hold 2 e-
2nd cloud can hold 8 e-
3rd cloud can hold 8 e-
You don’t need to know any higher orbits – you won’t be tested on higher elements.
You can depict any element in a Bohr model!

7. Which elements are these?

8. How do you know which atom?
The number of protons determines the identify of the atom!!! Four protons is an atomic number of 4 which is Beryllium!
4 p+ 5n 4e-

9. So how do we draw a Bohr model of… say…Sodium?
Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table)
Next place some orbits around it
P:11
N:12
P:11
N:12

10. Next figure out how many e- are in sodium (look at your periodic table). Place them in dots in the orbits
Remember!!
2 max in 1st orbit
8 max in 2nd orbit
18 max in 3rd orbit
Sodium has 11 electrons !!
they are the same as the protons
P:11
N:12

11. Draw a Bohr Model for an Argon atom
How many neutrons and protons does it have?
How many electrons does it have?

12. With a partner draw a Bohr model of:
Silicon Neon Magnesium

13. Valence Electrons Valence electrons and stability
Which atoms did you draw which had its valence electron shell full? _______________________
Every element wants to have a full outer shell – because then it is ______________________ and never has to react.
Every element wants to be like the __________________________ because they have full valences and are stable!!

14. Secret way to tell how many Valence e- in each element…
Look at your periodic table
Locate the 1 vertical row, the 2nd, then skip over to the 13th, 14th all the way to the 18th.
The last digit of each vertical row number is the amount of valence electrons
Column 1 – all elements in that row have 1 valence e- ( 1 e- in the last shell), Column 2 – all elements in that row have 2 valence e-.
Column 13 - all elements in that row have 3 valence e- , so row 18 has a full valence e- (except Helium which has a full outer orbit of 2e-)

15. Lewis Dot Diagrams…
Gilbert Lewis used a different model than Bohr, and he only showed the valence e- in it.
His model is called the Lewis dot structure .He put dots around the symbols so that we can see just the valence electrons for the elements (so we can easily see which e- are going to react)

16. The red dots show you the valence electrons in each element’s atoms

17. See the difference??... Lewis just shows the valence e-
P: 11
N:12 Na
Bohr model of Sodium Atom
Lewis Structure of Sodium Atom

18. when atoms have a full 8 valence orbit – we call it a stable octet
Lewis Dot Structures
when two electrons are together we call them a lone pair, they won’t react and make an atomic bond
The # of valence e- is … 8
8 e- is stable.
when atoms have a full 8 valence orbit – we call it a stable octet

19. How to draw …

20. Try some …
Remember, up to 4 e-, you put separately on each side of the symbol, once you get to 5, you have to start pairing up.
1) Magnesium 2) Nitrogen
3) Flourine ) Argon
Bonding pair N
Lone pair Mg F Ar

21. Things to KnOw…
Every element wants to have a full outer cloud– then they are stable – so…
if an element has it’s 1st orbit full and stable – it will have 2 valence e-
if an element has it’s 2nd , or 3rd orbit full and stable – it will have 8 valence e- (we call that a Stable octet)
Everything wants to bind together to get a maximum of 8 valence e- shared between them – then they are stable!!

22. Lewis Dot Structures
Draw the Lewis dot diagrams for the elements in the blank periodic table 