Bohr Models
and
Lewis Dot Structures
Recall that electrons orbit the
nucleus in energy levels
• Electrons orbit the
nucleus in rings.
• Layers of Rings
– Closest to nucleus
• Lower energy level
– Farthest from nucleus
• Higher energy level
• Each ring can hold only a
certain number of
electrons.
Rings hold certain numbers of
Electrons
• All of the rings together are
called the electron cloud.
• But separately, each ring
has its own “name.”
• First Energy Level
– Can hold 2 electrons
• Second Energy Level
– Can hold 8 electrons
• Third Energy Level
– Can hold 8 electrons
• Fourth Energy Level
– Can hold 2 electrons
Let’s Draw a Picture of an Argon Atom.
18P
14N
• You know how many
protons, electrons, &
neutrons are in an atom of
any element. Now, draw it.
How many e- are in the …
• First Energy Level?
• Second?
• Third?
• Fourth?
• This is called a Bohr
Model!!
Bohr Models
• We call this model the Bohr Model, after
Neils Bohr who developed it in 1915.
BOHR MODEL
•It has a circle in the center,
which represents the nucleus.
We write the number of protons
and neutrons in this circle.
•The rings surrounding the circle
are the energy levels. We draw
electrons on the energy levels.
Making a Model of an Atom
• Draw the nucleus, the
energy levels, and fill
in the electrons in each
energy level.
• ALWAYS FILL
ENERGY LEVELS
BEGINNING WITH
THE FIRST ENERGY
LEVEL!!
Let’s Try a Bohr Model of a
Lithium Atom.
Did you get it right?
If not, here’s a Review:
• Figure out how many Protons, Neutrons, &
Electrons are in the atom.
• Write the number of Protons & Neutrons in the
nucleus. Why there?
• Fill the energy levels in order beginning with FIRST
energy level! (2, 8, 8, 2)
• It’s OK to have empty energy levels on the outside.
One More Practice Problem…
Draw a Bohr model of Oxygen.
Did you get it right?
Term to Know
• Valence Electron –
number of electrons in
the outer energy level.
• What is the Valence Electron
number for Lithium?
• 1
• Oxygen?
• 6
Here’s a short-cut!
Lewis Dot Structures
• Only use the element’s
symbol and the
valence electrons.
• Write the symbol and
surround it with the
correct number of
valence electrons.
Lithium
Lewis Dot
Bohr Model
Oxygen
Lewis Dot
Bohr Model