How to draw a (Bohr)
model of an atom
Step 1: find the element on the
periodic table… Let’s try Sodium (Na)
Step 2: Determine the atomic number
(smaller of the 2 numbers)…
So, for Sodium (Na), the atomic # is 11.
• The atomic # tells us 2 things:
– Number of protons (= 11)
– Number of electrons (= 11)
Step 3: Determine the atomic mass (bigger of the 2
numbers) & round to the nearest whole number…
So, for Sodium (Na), the atomic mass is 22.99, but
rounded to the nearest whole number it’s 23.
• atomic mass = # of protons + # of neutrons
Step 4: Calculate the number of neutrons…
• atomic mass = # of protons + # of neutrons
• So… 23 = 11 + # of neutrons
• Which is the same as… 23 -11 = # of neutrons
• Therefore… 12 = # of neutrons
Now… to draw your Bohr model of the atom...
Sodium (Na)
Atomic number: 11
Atomic mass: 23
# of protons: 11
# of neutrons: 12
# of electrons: 11
First, draw your nucleus with the protons and neutrons….
Na
11 p+
12 n0
Now… to draw your Bohr model of the atom...
Sodium (Na)
Atomic number: 11
Atomic mass: 23
# of protons: 11
# of neutrons: 12
# of electrons: 11
Second, draw your first energy level, which can hold up to
2 electrons maximum….
Na
11 p+
12 n0
2 e-
Now… to draw your Bohr model of the atom...
Sodium (Na)
Atomic number: 11
Atomic mass: 23
# of protons: 11
# of neutrons: 12
# of electrons: 11
You still have 9 electrons left…
Draw a second energy level, which can hold up to 8
electrons maximum….
Na
11 p+
12 n0
2 e8 e-
Now… to draw your Bohr model of the atom...
Sodium (Na)
Atomic number: 11
Atomic mass: 23
# of protons: 11
# of neutrons: 12
# of electrons: 11
You still have 1 electron left…
Draw a third energy level, which can hold up to 8
electrons maximum….
But, you only have
1 electron left, so
this energy level
will not be full…
Na
11 p+
12 n0
2 e8 e1 e-