Electron Energy Levels

The electrons in an atom can only have certain definite (discrete) energies. These allowed energies are called energy levels. An electron cannot have an energy between two levels.The lowest energy level is the ground state. This is the most stable state, and it is where the electrons normally are. Higher levels are called excited states.Energy levels are usually given in electronvolts (eV). One electronvolt is the energy transferred when an electron moves through a potential difference of 1 V:1 eV = 1.60 × 10^-19 JAn electron that has just been freed from the atom, with no kinetic energy, is given an energy of zero. Because energy must be supplied to free an electron, every bound energy level has a negative value, and the ground state is the most negative.The energy levels of hydrogen are:n = 1 (ground state): −13.6 eV
n = 2: −3.40 eV
n = 3: −1.51 eV
n = 4: −0.85 eV
n = ∞: 0 eVThe levels get closer together as the energy increases towards zero.The ionisation energy is the energy needed to completely remove an electron from the ground state. For hydrogen it is 13.6 eV, which is 13.6 × 1.60 × 10^-19 = 2.18 × 10^-18 J.Every element has its own unique set of energy levels. This is why each element produces its own characteristic spectrum.