Bohr
Bohr worked with Rutherford to create the model that we now use to explain how atoms and molecules react. His post-doctoral work with Rutherford is based on quantum physics.
This sounds complicated, but simply means that he said each electron must have a specific amount of energy (quantum) and exists in a specific space around the nucleus.
The problem with Rutherford's model, was that it showed electrons moving in a curved path. ANY charged particle moving in a curved path should emit energy in the form of light BUT we know that every atom on earth is NOT constantly emitting light.
Bohr noticed that when hydrogen gas was given energy, it created a few bands of light (equivalent to specific wave lengths). This could not be explained by Rutherford's Planetary Model.
The model above shows that each orbit (energy level) can only hold electrons with a given amount of energy. In order for an electron to move to a different energy level, it must either give away some energy to the environment (a photon of light) OR absorb some energy from the environment ... we will discuss this further when we look at absorption and emission spectrums in the space unit of study!
IF you're interested in understanding the movement of celestial objects, read more here...
What does a Grade 9 Student need to know about this model?
- Bohr's model shows that electrons are stable (don't fly away)
- There are spaces around the atom that require that the electrons have a specific amount of energy (we are drawing these as circles and calling them orbits, although this is not the reality of the space they travel in)
- Each "orbit" has electrons with a specific amount of energy
- First energy level can only hold TWO electrons
- Every other energy level that we will learn about can hold EIGHT electrons