Neils Bohr

NEILS BOHR 1885-1962

       Neils Henrik David Bohr (October 7, 1885- November 18, 1962) was a Danish Physicist who made essential contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922.

       Bohr was borned in Copenhagen, Denmark, in 1885. His father, Christian Bohr, was a professor of physiology at the University of Copenhagen. His mother, Ellen Adler Bohr, came from a wealthy Jewish family. His brother, Harald Bohr, a mathematican and an Olympic footballer.

        Bohr and his wife, Margrethe Norluhd Bohr, had six sons. The oldest died because of a tragic boating accident and another died from childhood meningitis. His other sons went on to lead on successful lives. Aage Bohr was like his father who became a very succesful physicist and he also won a Nobel Prize in Physics in 1975.


Bohr's Model

        Neils Bohr developed the modern atomic model by proposing
that electrons occupied fixed orbits around the nucleus, called electron shells. This shells were at set distances from the nucleus ad these were the same for all element. The shells become larger the futher they are away from the nucleus, similar to the layers of the skin that make up an onion; the outermost layer is considerably larger than the ones closest to the core.

       He reasoned that larger shells could hold more electrons and proposed each shell could hold 2 n squared electrons where n is the shell number. So the first shell could hold 2x(1 squared)=2 electrons, the second shell 2x(2 squared) electrons and so on.

                               

      This gives the following sequence of numbers of electrons in shells: 2, 8, 18, 32, 50 etc. He also showed that elecctrons can move from a lower orbit (close to the nucleus) to a higher orbit (futher from the nucleus) by absorbing energy when heated, accounting for already known absorption spectra. These electrons would then lose that energy when allowed to cool, giving the emission spectra for different elements.

Bohr Atomic Model

Neils Bohr

Here are some videos and pictures of Neils Bohr's invention or the Bohr Atomic Model.

Explaining the Bohr Model

In general, the circumference equals n times the wavelength, where n is any positive integer. In the above figures the value of n is 1, 2 and 3 respectively. It turns out that these standing wave states for electrons correspond exactly to the "allowed" electron orbits in Bohr's model. So, Quantum Mechanics explains Bohr's ad-hoc model of the atom. Now we call the integer n the principal quantum number. Note that for the hydrogen atom it completely describes the state of the electron.

          
         "We are tracing the description of natural phenomena back to combinations of pure numbers which far transcends the boldest dreams of the Pythagoreans." -Neils Bohr



Sources: http://en.wikipedia.org/wiki/Niels_Bohr
              http://www.wordiq.com/definition/Niels_Bohr
              http://www.upscale.utoronto.ca/PVB/Harrison/BohrModel/BohrModel.html
              http://www.green-planet-solar-energy.com/atom-2.html