Bohr Models… O 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. Here is a typical Bohr model, what can you figure out from it?
O Bohr models show the nucleus in the center with the # of Protons (p) and Neutrons (n) in it O Around the nucleus, it shows the electrons in orbits or shells O Each orbit/shell can only hold a certain # of electrons and then it is full.
How many e- can each orbit hold? O 1 st orbit can hold 2 e- O 2 nd orbit can hold 8 e- O 3 rd orbit can hold 8 e- O 4 th orbit can hold 18 e- O You don’t need to know any higher orbits – we won’t be covering higher elements. O You can depict any element in a Bohr model!
Some Bohr models… Beryllium 4 p+ 5n 4e- Oxygen 8p+ 8n 8e- Aluminium 13 p+ 13 e- 14 n
So how do we draw a Bohr model of… say…Sodium? O Start with a nucleus, and put in how many protons and neutrons are in sodium (look at your periodic table) O Next place some orbits around it P:11 N:12 P:11 N:12
O 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
Draw a Bohr Model for an Argon atom O How many neutrons and protons does it have? O How many electrons does it have?
Valence Electrons 1. Valence electrons and stability O Which group on the periodic table, do you notice, always has all its valence electron shell full? _______________________ O Every element wants to have a full outer shell – because then it is ______________________ and never has to react. O Every element wants to be a __________________________ because they have full valence e-, and are stable!!
Secret way to tell how many Valence e- in each element… O Look at your periodic table O Locate the 1 vertical row, the 2 nd, then skip over to the 13 th, 14 th all the way to the 18 th. O The last digit of each vertical row number is the amount of valence electrons O Row 1 – all elements in that row have 1 valence e- ( 1 e- in the last shell), Row 2 – all elements in that row have 2 valence e-. O Row 13 - all elements in that row have 3 valence e-, so row 18 has 8 valence e-(a full outer orbit) except Helium which has a full outer orbit of 2e-)
Lewis Dot Diagrams… O Gilbert Lewis used a different model than Bohr, and he only showed the valence e- in it. O 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)
The red dots show you the VALENCE ELECTRONS in each element’s atoms
See the difference??... Lewis just shows the valence e- P: 11 N:12 Bohr model of Sodium Atom Lewis Structure of Sodium Atom Na
Lewis Dot Structures O Lewis dot structures are really simple – they are just the valence e- represented as dots around an element. O 2 electrons together is called a lone pair. The # of valence e- is … 8 8 e- is stable. when atoms have a full 8 valence orbit – we call it a stable octet
Try some … O 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. O 1) Magnesium2) Nitrogen 3) Flourine 4) Argon Mg N F Ar Bonding pair Lone pair
Things to KnOw… O Every element wants to have a full outer orbit – then they are stable – so… O if an element has it’s 1 st orbit full and stable – it will have 2 valence e- O if an element has it’s 2 nd, or 3 rd orbit full and stable – it will have 8 valence e- (we call that a Stable octet) O Everything wants to bind together to get a maximum of 8 valence e- shared between them – then they are stable!!
Lewis Dot Structures Draw the Lewis dot diagrams for the elements in the blank periodic table