Niels Bohr's model of the hydrogen atom.
Niels Bohr's model of the hydrogen atom, was the primary reason for the understanding of energy levels.Bohr was able to explain the bright line spectrum of hydrogen. Sparked by the recent discovery of the diffraction patterns, scientists believed electrons could be described as waves. Bohr hypothesized that energy is being added to the hydrogen gas in the electricity form, and then leaving the gas in the form of light. He figured the light rays to be quantized, meaning only certain frequencies of the light rays can be seen. In turn, he reasoned that the hydrogen atoms themselves were quantized and, that they only can exist in certain energy levels. When the atoms absorb specific amounts of energy, they exist for a small period of time in higher energy levels. But as soon as these atoms lose their energy, they move back down to the lower levels of energy. His theory went on to state how the hydrogen atom can move up and down the energy levels, one level at a time, and can never stop in between. Every hydrogen atom is made up of a single electron - proton system. Because the negative electron is attracted to the positive proton, potential energy is created inside the atom.
He figured that the farther away the electron is from the proton, the greater the potential energy is inside. In conclusion, since hydrogen atoms emit light energy in specific frequencies, the hydrogen atom must be within a specific energy level and nothing else. The different wavelengths help to determine the different colors emitted from the atom. The greater the wavelength, the faster the atom can be filled and jump to a higher level.
Bohr developed his theory after studying the work of Einstein's ideas on the photons of energy. He used these ideas to explain the amount of energy collected in the bright-line spectrum. He then used mathematics to determine the different energy levels of hydrogen.