1. How to draw a (Bohr) model of an atom

2. Step 1: find the element on the periodic table… Let’s try Sodium (Na)

3. 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)

4. 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

5. Step 4: Calculate the number of neutrons…
atomic mass = # of protons + # of neutrons
So… 23 = 11 + # of neutrons
Which is the same as… = # of neutrons
Therefore… 12 = # of neutrons

6. 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

7. 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-

8. 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 e-
8 e-

9. 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 e-
8 e-
1 e-