1. Atomic Theory Part 2

2. Where we left off… What we know (as of Rutherford/Chadwick):
Electrons are negative and have almost no mass and are distributed around the nucleus
Protons are positive & neutrons have no charge. Both are much heavier and are found in the nucleus

3. Where we left off…
After discovering the nucleus, Rutherford used existing ideas about the atom and proposed an atomic model in which the electrons move around the nucleus like the planets move around the sun.
Rutherford’s atomic model explained only a few simple properties of atoms. It could not explain the chemical properties of elements.
Neils Bohr, a student of Rutherford, developed a model that could better explain the behavior of the atom.

4. Neils Bohr
In 1913 Bohr changed Rutherford’s model to incorporate new knowledge about the atom and it’s ability to absorb or emit light.
Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.
Electrons orbit at certain fixed levels of energy, called energy levels
When electrons gain or release energy they can move up and down the energy levels
The amount of energy needed to move up or down an energy level is known as a quantum.

5. Neils Bohr You can think of energy levels like a ladder…
A person can climb up and down the ladder using the rungs, just like an electron can move up and down energy levels.
A person can’t stand between rungs, and an electron can’t be between energy levels.

6. Neils Bohr
Unlike a regular ladder, energy levels are NOT equally spaced!
The lower energy levels at the bottom and the higher energy levels are at the top
It takes a lot more energy to move between the low energy levels than it does to move between the higher energy levels

7. Neils Bohr’s Model
Neils Bohr’s model made a lot of improvement on the atom but we’re still not quite there... Later on, calculations showed that the electron didn’t move in a nice orbit like Bohr thought.

8. Erwin Schrodinger
In 1926 Schrodinger took those calculations and came up and solved a mathematical equation to describe the movement of electrons
This mathematical equation led to the creation of the quantum mechanical model
The quantum mechanical model still restricts the energy of electrons to certain levels.
The quantum mechanical model does not specify an exact path the electron takes around the nucleus.

9. Quantum mechanical model
The quantum mechanical model determines:
The possible energy levels an electron can have
How likely it is to find the electron in various locations around the nucleus of an atom.
It is similar to a ceiling fan –
you have a general idea
of where the blade is but
you don’t know where it will
be at any exact moment

10. Quantum mechanical model
Protons and neutrons are still in the dense nucleus
Electrons are still confined to energy levels
Electrons do not have an exact position or an orbit within the atom
Electrons are in the electron
cloud, which is the location they
are likely to be found in 90% of
the time. The darker the area
the more likely the electrons will
be there.