The Bohr – Rutherford Model of the Atom

Chemistry - Lesson 8

Experiments

There are two experiments that lead to the Bohr Model

1. Gold Foil Experiment

2. Hydrogen Absorption Spectrum

• ..\Links\Rutherford_s_Experiment_Nuclear_Atom.flv

• ..\Links\viewing_hydrogen_spectrum.flv

The Conclusions

• Protons and Neutrons make up a dense nuclear core• Electrons circle the nucleus in discrete shells or orbitals• Nuclear core is positively charged• Proton and Electron have opposite charges that are

equal in size• The shells can only hold specific numbers of electons• 2, 8, 8, 8….. (This is actually a simplification

Making Bohr – Rutherford Diagrams

Using these conclusions, we can draw a model of what the atom looks like.

1. Using a periodic table, find the number of protons and neutrons.

• Protons = Atomic Number • Neutrons = Atomic Mass –

Atomic Number

2. Put the protons and the neutrons in the nucleus of the atom.

Example – Oxygen

P = Atomic Number

= 8

N = Atomic Mass – Atomic Number

= 16 – 8

= 8

P=8

N=8

Now the electrons

3. Using the charge, find the number of electrons

• For now we will assume the atom is neutral (electrons = protons)

4. Put the electrons in the shells. When one shell is full start another shell

• Remember the maximum number of electrons for the shells is 2, 8, 8, 8…..

e = p = 8

P=8

N=8

Practice

What will the Bohr Rutherford diagram for Aluminum look like?

p = Atomic Number = 13

n = Atomic Mass – Atomic Number= 27 - 13= 14

Since the aluminum is neutral,e = pe = 13

P=13

N=14

Practice

What will the Bohr Rutherford diagram for Argon look like?

p = Atomic Number

= 18

n = Atomic Mass – Atomic Number

= 40 - 18

=22

Since the argon is neutral,

e = p

e = 18

P=18

N=22

P=18

N=22