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)

• atomic mass = # of protons + # of neutrons

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.

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: 11Atomic mass: 23# of protons: 11# of neutrons: 12# of electrons: 11

First, draw your nucleus with the protons and neutrons….

Na11 p+

12 n0

Now… to draw your Bohr model of the atom...Sodium (Na)

Atomic number: 11Atomic 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….

Na11 p+

12 n0

2 e-

Now… to draw your Bohr model of the atom...Sodium (Na)

Atomic number: 11Atomic 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….

Na11 p+

12 n0

2 e-

8 e-

Now… to draw your Bohr model of the atom...Sodium (Na)

Atomic number: 11Atomic 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 have1 electron left, sothis energy levelwill not be full…

Na11 p+

12 n0

2 e-

8 e-

1 e-