1. When current is passed through a gas at low pressure, the potential energy of some of the gas increases.
The ground state of an atom is the lowest possible energy state. As atoms get excited, they gain potential energy. As they return to ground state, they give off a photon of EM.
Neon signs use this technology to get their characteristic glow!

2. A line emission spectrum is the group of specific frequencies of light that are emitted by an element when atom is excited and then goes back to the ground state.

3. When hydrogen gas has a current run through it in a vacuum tube, it glows with a pink light.
Scientists expected to see a continuous spectrum of visible light when they passed it through a prism.
Instead they saw only specific frequencies – the hydrogen line spectrum. The Lyman, Balmer, and Paschen series of lines are named for the scientist who discovered that portion of the spectrum (IR/visible/UV)

4. The fact that Hydrogen only emits light at certain frequencies indicates that Hydrogen is emitting photons only in specific ENERGY AMOUNTS, according to
E = h*v
The energy differences between an atom’s energy states must be fixed (specific values)

5. Neils Bohr proposed an explanation to the Hydrogen line emission spectrum, stating that electrons can circle the nucleus only in specific paths.
The energy differences of these paths increased further from the nucleus, and as an electron went from an excited state to ground state, it gave off a photon of EM with the associated energy difference.
Bohr’s model only accurately explained Hydrogen, not elements with more than one electron…