Up to this point, we have only discussed the nucleus. In advanced atomic theory, we discuss the electrons and their behavior.

Bohr’s experimentAtoms make pretty colors when their

electrons are excited.If you measure the wavelengths of those

colors, you can calculate the energy.

Why are there different energies of light which come from atoms?An electron can be excited from one energy

level to the next.An electron cannot be excited half way

between two energy levels.

We do not see light when an electron is excited. When do we see light?

We see light when the elctron moves from a higher energy state toA lower energy state. We observe the energy loss as light.

If I climb onto a desk, it is pretty silent. When I fall off the desk, soundis emitted. If I were an electron, I would emit wavelengths of light insteadof wavelengths of sound.

What is Bohr’s model of the atom called?The planetary model

What is wrong with the Bohr model?

When you look carefully at the emission spectra of atoms, you notice that there are multiple similar lines. What does that imply?The Bohr model has two problems. One

problem is that it doesn’t make sense because the electrons would begin a death spiral into the nucleus.

The second problem is that the presence of multiple lines implies that there are similar energy levels (which are not exactly the same as each other.

Quantum Mechanics.It is possible to describe the likely location of

electrons by using a series of mathematical functions.

Electrons exist in “orbitals” where they can be found with a 90% probability.

It is not possible to know both the location and the speed of an electron at the same time because by observing one, you change the other.