1. Section 4.3 Modern Atomic Theory

2. Niels Bohr
Agreed with Rutherford’s model of the atom.
He agreed that there was a nucleus surrounded by a large volume of space.
His model is often known as the planetary model because it resembled the solar system.
His model went one step further than Rutherford’s model because it focused on the electrons.
He stated that the electrons move with constant speed in fixed orbits around the nucleus.

3. He thought that electrons had a specific amount of energy.
This possible energy an electron can have in an atom is called energy levels.
Similar to the rungs on a ladder or steps on a staircase.
As you go up the stairs you go to a higher energy level.
An electron in an atom can move from one energy level to another when the atom gains or loses energy (Picture of model page 115).

4. Evidence of these energy levels is shown when the electrons give off the energy in the form of light (flame test lab and fireworks)
Electrons are usually in their normal energy level called the ground state. When they absorb energy they move to a higher level called the excited state.
When the electrons fall back to their ground state the energy is released in the form of light.
Different elements emit different colors.

5. Drawing a Bohr Model NEUTRONS AND PROTONS:
Neutrons and protons are located in the nucleus. Write the number of protons and neutrons inside the nucleus using the symbols ‘p+’ and ‘n0’.

6. ELECTRONS:
Electrons are located in orbitals surrounding the nucleus.
Number of electrons = Number of protons
How many electrons can fit in each orbital? 
1st orbital = 2 electrons 
2nd orbital = 8 electrons 
3rd orbital = 8 electrons 
4th orbital = 18 electrons

7. The LOWER orbital MUST be full before you start filling the higher orbitals
(ie the 1st orbital MUST have two electrons in it BEFORE you start filling the 2nd orbital)

8. Examples