2. Line Emission Spectrum If this light is separated with a prism, it separates into a series of specific frequencies of light. This series of frequencies is highly specific for each type of atom and is called a line-emission spectrum.

3. These line-emission spectrums are often used to identify unknown elements. Prior belief held that excited atoms should return to their ground states smoothly and emit light in a continuous spectrum rather than in bands of specific frequencies.

4. Why bands rather than a continuous spectrum? Characteristic wavelengths of light are produced by atoms because there are specific amounts of energy between the various excited states and the ground state. Each jump produces a photon of light equal in energy to the difference between the energy levels.

5. Each photon has a specific frequency and therefore a specific wavelength. E photon = h Each type of atom has its own series of specific excited energy states. The pattern is fixed and specific for each element.

6. Bohr Model of the H atom Niels Bohr explained the line-emission spectrum of hydrogen in 1913. He linked the various energy states of hydrogen to the position of its electron. When the atom was in its ground state, the electron was in an orbit close to the nucleus.

7. As energy was provided, the electron jumped to an orbit farther from the nucleus. This new orbit was a specific distance from the nucleus. The electron could not exist between the orbits.

8. Bohr’s model continued Even more energy could knock the electron still further from the nucleus to other orbits. As the electron falls back toward the nucleus, a photon of light (equal to the amount of energy required to knock the electron out of orbit) is emitted from the atom.

9. This is why the light produced by hydrogen was in such precise wavelengths. However, Bohr’s model did not explain the line emission spectra for atoms with more than one electron. This was left to the Quantum theory.

10. The Quantum Model of the Atom

11. Louis de Broglie The behavior of light as both a particle and a wave led one scientist, Louis de Broglie, in 1924 to hypothesize that electrons behaved in a similar fashion. He said that the definite energy states of electrons corresponded to how waves behave when confined to an enclosed space.

12. In the case of the atom, the enclosed space was the region around the nucleus. The wave/particle behavior of electrons was later confirmed by experiments.

13. Werner Heisenberg de Broglie’s led to a new interest in where electron actually were located around the nucleus. A new hypothesis by Werner Heisenberg in 1927 offered a paradox for scientists trying to locate electrons.

14. Heisenberg uncertainty principle- states that it is impossible to absolutely simultaneously determine both the position and velocity of an electron or any other particle. This hypothesis turned out to be absolutely correct.

15. What did the uncertainty principle mean: In other words, the act of looking for an electron distorted its position. Scientists realized that the best they could do was establish areas around the nucleus that had a high probability of containing an electron. These areas of “probable” electron location are called orbitals.

16. Quantum Theory The charting and prediction of the probable paths of electrons around the nucleus is called the Quantum Theory. It uses mathematical formulas to describe the wave- like movement of electrons around the nucleus and determines the shape and location of their orbitals. The first scientist to mathematically describe the probable positions of electrons was Erwin Schrodinger, in 1926. Orbitals, however, are not the simple planet-like orbits their name suggests.