Summary of Flame Testing and Bohr’s Quantum Model of the Atom

Who? Niels Bohr Copenhagen, Denmark October 7, 1885- November 18, 1962 Occupation: Professor of Theoretical Physics at Copenhagen University Won the Nobel Prize for his Atomic Model (Planetary Model of the Atom)

What Did He Do in 1913? Proposed that electrons in atoms exist in orbits at discrete distances from the nucleus The orbits represent specific energies and are called energy levels (2-d) or energy shells (3-d). This model shows that energy in matter is quantized or can only be absorbed and released in specific small amounts. The exact amounts of energy absorbed and released are specific to each type of atom.

Continued… When an atom absorbs certain specific frequencies or energies of electromagnetic radiation, the electrons obtain a higher-energy orbit farther from the nucleus (the excited state). Each type of atom can only absorbs certain frequencies and energies of radiation. Eventually, The electrons return back to a lower-energy orbit (the ground state) and release the energy as photons of electromagnetic radiation. Each photon carries a specific amount or quantum of energy. The released photons are seen as spectral lines in an atomic emission spectrum!

E = E higher-energy orbit – E lower-energy orbit = E photon = h Picture of Bohr Model E = E higher-energy orbit – E lower-energy orbit = E photon = h

Why do we see a discontinuous emission spectrum? Each type of atom can only absorb and release certain frequencies and energies of electromagnetic radiation related to the exact energy differences between the energy levels in that specific atom. If matter (and atoms) could absorb and release any and all possible amounts of electromagnetic radiation energy, we ought to always get a continuous emission spectrum, but we never do.

Other types of photons are also released by atoms… Other types of photons are also released by atoms….producing other spectral lines but they are invisible to the naked eye!

Importance and Limitations Bohr’s atomic model explains the atomic emission spectra of hydrogen the best. Bohr’s atomic model is the first quantum model of the atom. It explains how energy and matter interact at the atomic level and describes how atoms can only absorb and release certain energies. Bohr’s model implies that electrons orbit the nucleus in circular orbits like planet orbit a sun (but really they do not). Bohr’s model does not accurately explain the chemical properties of elements.

Application of Spectroscopy in Geology X-ray map of Calcium in a garnet crystal in a garnet schist.