1. 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 1913.

2.  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 orbits or shells  Each orbit/shell can only hold a certain # of electrons and then it is full.

3. How many e- can each orbit hold?  1 st orbit can hold 2 e-  2 nd orbit can hold 8 e-  3 rd orbit can hold 8 e-  4 th orbit can hold 18 e-  You don’t need to know any higher orbits – we won’t be covering higher elements.  You can depict any element in a Bohr model!

4. Some Bohr models… Lithium 4 p+ 5n 4e- Oxygen 8p+ 8n 8e- Aluminum

5. 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

6.  Next figure out how many e- are in sodium (look at your periodic table). Place them in dots in the orbits P:11 N:12 Remember!! 2 max in 1 st orbit 8 max in 2 nd orbit 8 max in 3 rd orbit 18 max in 4 th orbit Sodium has 11 electrons !! they are the same as the protons

7.  The outermost electrons – the ones in the last shell/orbit are called valence electrons  Valence e- are important because when atoms react, it is the valence e- that do all the moving !! P:11 N:12 * Think valence penguins

8. How many Valence e- in these Bohr models?? 2 ve- 6 ve- 3 ve-

9. Valence e- what do we know…  Which group on the periodic table, do you notice, always has all it’s valence electron shell full?  The Noble Gases. This is very significant… Why??  Because every element wants to have a full outer shell of valence e- – because then it is completely stable and never has to react. Every element wants to be a noble gas

10. What about Bohr models of Molecules?  Eg. What is this compound? 8 p+ 8 n 1p+ 0n 1p+ 0n

11.  Can you draw the Bohr model of H2?  Why would 2 Hydrogens be happy to bond together? 1p+ 0n 1p+ 0n