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.
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.
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!
Some Bohr models… Lithium 4 p+ 5n 4e- Oxygen 8p+ 8n 8e- Aluminum
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
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
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
How many Valence e- in these Bohr models?? 2 ve- 6 ve- 3 ve-
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
What about Bohr models of Molecules? Eg. What is this compound? 8 p+ 8 n 1p+ 0n 1p+ 0n
Can you draw the Bohr model of H2? Why would 2 Hydrogens be happy to bond together? 1p+ 0n 1p+ 0n