The Bohr Model (1913) revolve sun energy 1913 – A Danish scientist Niels Bohr suggested that the electrons ____________ around the nucleus like the planets revolve around the _______. In Bohr’s model each electron has a certain amount of ___________ that is defined by its path around the nucleus. These defined orbits are called energy levels. revolve sun energy

Bohr’s theory Planetary Model: Three rules: Electrons orbit the nucleus like planets orbit the sun Electrons can “jump” between orbits by _________ or _________ photons Theory explained the line spectra of H Three rules: Electrons only exist in certain allowed orbits Within an orbit, the electron does not _______ Radiation (light) is emitted or absorbed when changing orbits radiate absorbing emitting

Atomic Spectra When electrons absorb energy they move to higher energy levels, and when electrons lose energy by emitting light they return to their ground state.

Hydrogen Line Spectrum

Quantum theory of the atom Lowest energy state = “ground state” n1 In hydrogen, n1= -13.6 eV Higher states = “excited states” n2, n3, n4… Energy of orbit calculated by Photon energy equals difference in state energies 1 eV=1.6E-19 J

The Energy of a Photon The energy of a photon is proportional to the frequency of light and can be calculated using Plank’s constant E = hf, where h = 6.63 x 10-34 Js How much energy would red light have with a frequency of 4.57 x 1014 Hz?

How does this tie in with Bohr’s Model The light emitted from an electron moving from a higher to a lower energy level has a frequency proportional () to the energy change of the electron moving between energy levels

An electron in a hydrogen atom jumps from the exited energy level n = 4 to n = 2. What is the frequency and wavelength of the emitted photon?