Niels Bohr and
Bohr Diagrams
Who is Niels Bohr?
• Niels Bohr was a Danish scientist born in 1885.
• Bohr received a Nobel Prize in Physics in 1922 for
his contribution to the Atomic Model.
• He proposed that electrons revolve in stable
orbits(shells) around the nucleus of an atom based
on the energy levels of its electrons.
• This model expanded on Ernest Rutherford’s model
of 1911.
Comparing Rutherford and Bohr’s models
of the atom
Atomic Structure Review
• Atoms have a nucleus that contains Protons and
Neutrons
• Electrons are contained in orbits or shells that
surround the nucleus
• An atom is made of mostly empty space
• Protons have a positive (+) charge
• Electrons have a negative (-) charge
• Neutrons are Neutral
Bohr Models are
NOT Boring!
How to Draw Bohr Diagrams
Bohr Diagrams
1) Find the element on the periodic table.
2) Determine the number of electrons – How do we
do this?.
3) This is how many electrons you will draw.
Bohr Diagrams
1
• Find out which period
(row) your element is in.
2
3
4
5
6
7
•Elements in the 1st period
have one energy level.
•Elements in the 2nd period
have two energy levels,
and so on.
Bohr Diagrams
1) Draw a nucleus with
the element symbol
inside.
C
P+ = ?
N0 = ?
2)Write the number of
Protons and Neutrons the
element has inside the
nucleus. Put a + by the P
and a little 0 by the N.
Why do we do this?
Note: Round mass to nearest 1 when figuring neutrons.
The electron shells surrounding the nucleus
each hold a particular number of electrons.
Shells are named with letters:
1 = K shell
2 = L shell
3 = M shell
4 = N shell
5-7 = O, P, Q
= 2 electrons
= 8 electrons
= 8 electrons
= 18 electrons
= up to 32 electrons
Remember: The outer shell of an atom (no
matter what letter) can only hold 8 electrons!
What does this mean for Elements with NOPQ shells?
Bohr Diagrams
C
P+ = 6
N0 = 6
1) Carbon is in the 2nd period,
so it has two energy levels,
or shells.
2) Draw the shells around the
nucleus.
Bohr Diagrams
1)
C
P+ = 6
N0 = 6
2 e-
Add the electrons.
2) Carbon has 6 electrons.
3) The first shell can only
hold 2 electrons.
4) Write the number of
electrons that shell holds
and e- for electrons an
their charge.
5) How many electrons are
in the outer shell?
Bohr Diagrams
1)
C
P+ = 6
N0 = 6
2e-
4e-
Since you have 2 electrons in
the first shell, you need to add
4 more.
2) These go in the 2nd
shell.
3) Again, write e- and the
number of electrons.
Bohr Diagrams
1) Check your work.
C
P+ = 6
N0 = 6
2e-
4e-
2) You should have 6 total
electrons for Carbon.
3) Only two electrons can fit in
the 1st shell.
4) The 2nd shell can hold up to 8
electrons.
5) The 3rd shell can hold 18, but
the elements in the first few
periods only use 8 electrons.
But do electrons clump up
like this model shows?
Why/why not?
Bohr Diagrams
1)
2)
3)
Add the electrons.
Carbon has 6 electrons.
The first shell can only hold 2
electrons.
To correctly draw the dots… Draw an X over the diagram and start at the far right
working counterclockwise.
Bohr Diagrams
1)
2)
3)
Add the electrons.
Carbon has 6 electrons.
The first shell can only hold 2
electrons.
To correctly draw the dots… Draw an X over the diagram and start at the far right
working counterclockwise.
Bohr Diagrams
1)
2)
3)
Add the electrons.
Carbon has 6 electrons.
The first shell can only hold 2
electrons, and the electrons
exist opposite one another.
To correctly draw the dots… Draw an X over the diagram and start at the far right
working counterclockwise.
Bohr Diagrams
1)
2)
3)
Since you have 2 electrons
already drawn, you need to
add 4 more.
These go in the 2nd shell.
Add one at a time -starting on
the right side and going
counter clock-wise.
Bohr Diagrams
1)
2)
3)
Since you have 2 electrons
already drawn, you need to
add 4 more.
These go in the 2nd shell.
Add one at a time -starting on
the right side and going
counter clock-wise.
Bohr Diagrams
1)
2)
3)
4)
5)
Check your work.
You should have 6 total
electrons for Carbon.
Only two electrons can fit in
the 1st shell.
The 2nd shell can hold up to 8
electrons.
The 3rd shell can hold 18, but
the elements in the first few
periods only use 8 electrons.
Your turn!
You will each be given an
element from the first 20
elements of the Periodic table.
You will need to draw the
electron configuration of your
element.