Chemistry pt. 5: The Bohr model

Atoms, it is nearly impossible as you cannot see atoms due to your naked eye, so we use models to visualize these small atoms.

These models can be used to predict and explain the behaviour of atoms.
All models are simplified to a degree, either for simplicity, visibility or usability, if we were to make it more accurate it would be the real thing.

What is a circle with rings around it, those rings are commonly named "shells", they are for the electron atoms which are dots on the shellsand depending on how far the dots are from the centre circle, it means that the electron atom is different.
Something to keep in mind is that the first shells can only support 2 electron dots, and the others can only hold 2 as well.
It uses an N system as the first shell has a value of 1N, while the second has 2N, and then the third has 3N.

1N has 2 Electrons, 2N as 8. Do keep in mind that these are not the actual positions of electrons.

Some elections can only exist on certain energy levels, we use a system named EV or an energy level diagram, the diagram can show us what energy the election is at without needing to draw dots on the Bohr model. 
Let's say our imaginary atom has levels of 0ev, 4ev, 6ev and 7ev.
So in this situation, the election can only exist on the shell that has, 0ev, 4ev, 6ev and 7ev, and cannot exist in between energy levels as it cannot exist on say 4.7ev. And cannot exist on any other shell.

Let's say the atom starts at 0ev, or "The ground state".
How does an election go from the ground state to an even level?. First, a photon with 4ev must strike the election, and then the election will absorb the photon, thus causing the election to be removed from the ground state and instead on the EV level of 4ev.

Valence electrons are electrons that are highly important as it is the outermost shells of the atom, and an atom's outer shell is the most important in chemistry.
A full Valence shell has 8 electrons or 4 pairs.