Download Bohr Model Notes - Northwest ISD Moodle

Unit: Chemistry
Notes: Bohr Models
Let’s look at the element Magnesium or Mg.
12
Atomic Number
Mg
Symbol
Magnesium
Atomic Mass or Mass Number
24.31
A
12
=
=
p
12
=
=
e
12
M
24
-
A
12
=
=
n
12
By using A=p=e M-A=n, we are able to determine that Magnesium has 12 protons, 12 electrons
and 12 neutrons.
When drawing Bohr models,
protons and neutrons are placed
in the nucleus.
Electrons are placed in energy
levels (orbitals) outside the nucleus.
 2 electrons can fit in the first energy level.
 8 electrons can fit in the second energy level.
 18 electrons can fit in the third energy level.
Valence Electrons – electrons found in the
outermost energy levels. Magnesium has 2
valence electrons.
Rule of Eight – Elements that have the maximum number of electrons in their outermost energy
levels (energy levels are full) are mostly non-reactive or inert.
Advantages of a Bohr Model
The model shows the number and the location
of protons, neutrons and electrons in the atom.
Limitations of a Bohr Model
The model does not show the approximate size
of each subatomic particle or any movement.
For more information, you can read pages 36-49 in your Glencoe Science Book.