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?
Slide 4
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.
Slide 5
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 dont need to know any higher orbits we wont be
covering higher elements. O You can depict any element in a Bohr
model!
Slide 6
Some Bohr models Beryllium 4 p+ 5n 4e- Oxygen 8p+ 8n 8e-
Aluminium 13 p+ 13 e- 14 n
Slide 7
So how do we draw a Bohr model of saySodium? 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
Slide 8
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
Slide 9
Draw a Bohr Model for an Argon atom O How many neutrons and
protons does it have? O How many electrons does it have?
Slide 10
Practice Blank Periodic Table
Slide 11
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!!
Slide 12
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-)
Slide 13
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)
Slide 14
The red dots show you the VALENCE ELECTRONS in each elements
atoms
Slide 15
Lewis Dot Structures
Slide 16
See the difference??... Lewis just shows the valence e- P: 11
N:12 Bohr model of Sodium Atom Lewis Structure of Sodium Atom
Na
Slide 17
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
Slide 18
How to draw
Slide 19
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
Slide 20
Things to KnOw O Every element wants to have a full outer orbit
then they are stable so O if an element has its 1 st orbit full and
stable it will have 2 valence e- O if an element has its 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!!
Slide 21
Lewis Dot Structures Draw the Lewis dot diagrams for the
elements in the blank periodic table