1. Parts of an Atom,
What a BOHR….
Learning to draw Bohr diagrams.

2. Atomic Number
 Typically
located above the element’s
symbol.
 As the table progresses from left to
right, and top to bottom, the atomic
number of the elements increases by
one for each element.
 This number tells us how many protons
there are in the nucleus of each
element.

3. What is the atomic number for
Carbon?
6
C
12.011

4. How many protons does Carbon
have? (think of it’s atomic #)
6
C
12.011

5. How do we determine the
number of neutrons?
Round:
12.001= 12
1. Round the
atomic mass
2. Subtract the
Atomic number
from the atomic
mass.
6
C
12.011
Subtract:
12-6= 6
ANSWER:
6 protons
and
6 neutrons!

6. What about the number of
electrons??
We know that
an atom is
neutral overall.
Electrons are
negative…
protons are
positive…
6
C
12.011
How many
electrons do
we need to
cancel out the
positivity of the
protons?
You guessed it!
The same as
the number of
protons!

7. Let’s try it with another element:
10
Ne
20.180
Ne (Neon):
Atomic number?
Number of Protons?
Atomic mass?
Number of neutrons?
Number of electrons?

8. Time for Bohr Diagrams!
 Remember
the sequence 2,8,8?!?!
 This is when we need it!
 Hold
onto your hats folks! This is
exciting!

9. Three easy steps to making a
Bohr diagram:
Determine the number of protons,
neutrons and electrons.
2. Write the number of protons and
neutrons in the center.
3. Draw the electrons in the shells
around the nucleus following the
sequence 2,8,8. (they need to be in
pairs, drawn one at a time)
1.

10. Let’s try it all together!

11. Helium: Atomic# 2, Atomic Mass 4 amu
2+
2n
Protons = 2
Neutrons = 2
Electrons = 2

12. Lithium: Atomic# 3 Atomic mass 6.9 amu
3+
4n
Protons = 3
Neutrons = 4
Electrons = 3

13. Magnesium: atomic# 12,
mass 24amu
12+
12n
Protons = 12
Neutrons = 12
Electrons = 12

14. That wasn’t too hard, was it??
Now it’s time for you to practice!