Here, I took this straight from the notes I took back when I learned this. If you need any more clarification, just say so.
Bohr: Planetary modelTheorized that E- travel in specific orbits around the nucleus.The further an E- is from the nucleus, the higher its “energy.”The number of E- in the outermost orbital determines the reactivity of an element.
Bohr's model was a nucleus with concentric circles going around it representing the energy levels (where the electrons are in the atom). He was the first to demonstrate that the electrons in an atom orbit the nucleus, rather than stay in a consistent position. Google "Bohr Atomic Model" if you need any visual clarification. Hope I helped, and let me know if you need anything else!
