Niels Bohr
“The opposite of a correct statement is a false statement. But the
opposite of a profound truth may well be another profound truth.” (Niels Bohr)
Niels Bohr (1815 -1962) was a physicist from Denmark who was responsible for important developments in modern science. He is most known for his ideas on atomic structure but his first project was the precise determination of surface tension in water, which he got a gold medal for from the Academy of Sciences.
Bohr’s model of the atom shows that protons, positively charged particles, are in the nucleus and electrons, negatively charged particles, orbit the nucleus in rings. The further out the ring is from the nucleus, the more electrons can fit on it. He also discovered that the amount of electrons on the outermost ring around the nucleus determined certain properties of a metal. His atomic theory led him to the prediction that there was an element that had not been discovered yet and had specific properties. That element was discovered at his institute and called hafnium.
He later used his knowledge of the atomic structure to when studying atomic radiation. Bohr was able to show that only Uranium-235 could undergo fission with slow neutrons and he explained why a heavy nucleus could undergo fission when taking on an extra neutron. These are both very important to nuclear energy.
“Max Planck (1858-1947) had proposed that radiation is emitted or absorbed by atoms in discrete units or quanta of energy. Bohr applied this quantum theory to the nuclear atom to explain why elements emit radiation at precise frequencies that give set patterns of spectral lines. He postulated that an atom may exist in only a certain number of stable states, each with a certain amount of energy; the emission or absorption of energy may occur only with a transition from one stable state to another. Electrons normally orbit the nucleus without emitting or absorbing energy. When a transition occurs, an electron moves to a lower or higher orbit depending on whether it emits or absorbs energy. In so doing, a set number of quanta of energy are emitted or absorbed at a particular frequency.” (HDSD)
His ideas show that shells of electrons orbit nuclei of atoms and they have specific quantum numbers based on their orbits. His theory succeeded in determining the frequencies of spectral lines from the elements. This allowed him to explain the Periodic Table more accurately by understanding electron structures. This is what led him to his prediction of element to be discovered and called hafnium.
Bohr was able to explain how fission works. He said that the nuclear particles are pulled together the same way water molecules are pulled together in a water droplet. He also said that when an atom takes on an extra neutron, the energy that has been absorbed in this process could cause the split into two equal sizes. His prediction of different results from Uranium-235 and Uranium-238 gaining a neutron proved his theory correct.
During World War II, he fled Denmark and came to the United States. He started working on the Manhattan Project as an advisor at Los Alamos, New Mexico. This project was America’s first atomic bomb creation. After the war was over and he had seen the destruction caused by it, he became an avid advocate against the use of nuclear weapons. He believed that all countries should be open about their capabilities, referring to their nuclear power.
Bohr used theories and models from other scientists and improved them as well as combined them to come up with new theories. Anyone who has taken a chemistry class can thank him for the proper atomic structure.
The Nobel Foundation, Nobel Prize.org
http://nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html
The Hutchinson Dictionary of Scientific Biography
http://www.chemcool.com/biography/bohr.htm
