Bohr Models and
Lewis Dot Diagrams
Science 10
Niels Bohr
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 1st
O
O
O
O
O
orbit can hold 2 e2nd orbit can hold 8 e3rd orbit can hold 8 e4th orbit can hold 18 eYou 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…
Oxygen
8p+ 8n 8e-
Beryllium
4 p+
5n 4e-
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)
P:11
N:12
O Next place some orbits around it
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
Remember!!
2 max in 1st orbit
8 max in 2nd orbit
8 max in 3rd orbit
18 max in 4th orbit
Sodium has
11 electrons !!
they are the
same as the
protons
P:11
N:12
Draw a Bohr Model for an
Argon atom
O How many neutrons and protons does it
have?
O How many electrons does it have?
Practice
Blank Periodic Table
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 2nd, then skip over
to the 13th, 14th all the way to the 18th.
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
Lewis Dot Structures
See the difference??...
Lewis just shows the valence
eP: 11
N:12
Bohr model
of Sodium
Atom
Na
Lewis
Structure of
Sodium Atom
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
How to draw …
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) Magnesium
Mg
3) Flourine
F
2) Nitrogen
Bonding
pair
N
4) Argon
Ar
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 1st orbit full and
stable – it will have 2 valence eO 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)
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 