Bohr Model & Lewis Dot Diagrams
Both are valuable in a different way!
Recall...
 There are two models of the atoms we will be using in class.
 Bohr Model
 Lewis Dot Structure
Bohr Model
 The Bohr Model shows all of the particles in the atom.
 In the center is circles. Each circle represents a single
neutron or proton. Protons should have a plus or P written
on them. Neutrons should be blank or have an N.
 In a circle around the nucleus are the electrons. Electrons
should have a minus sign or an e.
 You can’t just shove all of the electrons into the first orbit of
an electron.
 Electrons live in something called shells or energy levels.
 Only so many can be in any certain shell.
 The electrons in the outer most shell of any element are
called valance electrons.
Draw a Bohr Model for Lithium
 Drawing a Lithium atom
1. look at the Periodic Table
determine the number of protons & neutrons
(protons = the atomic number)
(neutrons = Atomic mass minus number of protons)
determine the number of electrons
(electrons match the number of protons for neutral atoms)
2. add protons, neutrons and electrons to their proper
positions
Try drawing a Bohr Model for the following elements:
a)
b)
c)
H
He
O
Bohr Diagrams can become crowded!
Lewis Dot Diagrams
 The Lewis Dot Structure is a bit different from the Bohr
model.
 It only shows the element symbol and it’s outer most
electron shell.
 Step 1: Write the Element Symbol
 Step 2: Find the number of electrons in the
outermost energy level of the Bohr Model
(Valence Electrons)
 Step 3: Place the electrons (dots) around the
symbol in clockwise order so that there are no
more than 2 electrons per side.
Lewis Diagrams solve the
“crowding” problem
Summary
 Bohr models are good because they show the energy level of
all electrons in an atom.
 Lewis models are good because they eliminate the “crowded’
picture for elements with many subatomic particles (protons,
neutrons, and electrons)
Presentation Quiz
Try drawing a Bohr Model for the following elements:
a)
b)
c)
H
He
O
Try drawing a Lewis Model for those elements:
a)
b)
c)
H
He
O