Gerhard Herzberg

Gerhard Heinrich Friedrich Otto Julius Herzberg was born on December 25, 1904 in Hamburg, Germany.  His father was a businessman and worked for a small shipping company.  He died when Herzberg was still young.  After his father's death he lived briefly with his uncle in Frankfurt, but he did poorly in school and was homesick so he returned to live with his mother.  In Hamburg he attended the Realgymansium de Johanneums, where he had excellent teachers and developed an interest in astronomy and atomic physics.  He studied astronomy by reading textbooks from public libraries and with a friend made a crude telescope, but he was unable to pursue a career in astronomy for financial reasons.  With a fellowship from industrialist Hugo Stinnes he was able to attend the Technische Universtat Darmstadt, graduating with a Dr.Ing. in 1928.  After graduation he did postdoctoral work at Gottengen University and Bristol University under James Franck, Max Born and John Lennard-Jones.

After completing his postdoc he returned to Technishche Universtat Darmstadt as a pirvatdozant (lecturer).  In 1935 Herzberg was forced to flee Germany because of his Jewish wife, and he took a position as a guest lecturer at the University of Saskatchewan in Saskatoon, Saskatchewan, which was almost immediately made permanent. Herzberg remained at the University of Saskatchewan until 1945 when he became professor of spectroscopy at Yerkes Observatory at the University of Chicago, where he remained until 1948.  In 1948 he returned to Canada as the principal research officer and then director of the Division of Physics at the Canadian National Research Council.  In 1955 the Division of Physics of the Canadian National Research Council was split into two divisions, pure and applied physics and Herzberg remained president of the pure physics division.  In 1969 he was made distinguished scientist of the recombined Division of Physics of the Canadian National Research Council.

Herzberg's research dealt with spectroscopy and determining molecular geometries using spectroscopy.  From his doctoral thesis, on the spectrum of nitrogen gas, and throughout his career he determined spectra of various chemicals and from these data he was able to determine their geometry.  Because of Herzberg's work spectroscopy is a tool that chemists can use to determine the identity of a chemical.  Different molecules absorb and emit characteristic wavelengths of electromagnetic radiation determined by their structure.  Chemists use these characteristic absorbancies and emissions to determine the structure and identity of molecules.  At Yerkes Observatory Herzberg applied his knowledge of spectroscopy to determine the gasses present in planetary atmospheres.  He is author of the four volume Molecular Spectroscopy and Molecular Structure which has been called the spectroscopist's bible.  In 1971 Herzberg was awarded the Nobel Prize in chemistry for "his contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals".

Other honors won by Herzberg include election to the Canadian National Academy of Science in 1939 and the Royal Society of London in 1951.  Other awards won by Herzberg include the Willard Gibbs Award from the American Chemical Society, the Order of Canada, and the Royal Medal from the Royal Society of London.

Herzberg died on March 3, 1999 at the age of 94.


References:

Interview of Gerhard Herzberg by  Brenda J. Weinnwisser on February 28 and March 2, 1989, Niels Bohr Library and Archive, American Institute of Physics, aip.org.

Black, Harry; Canadian Scientists and Inventors: Biographies of People Who Made a Difference; Pembroke Publishers Ltd.; 1997

Devorkian, David; "Gerhard Herzberg, 1904-1999"; Bulletin of the American Astronomical Society; (2000)35:1669-1670

Gerhard Herzberg Nobel Biography

Gerhard Herzberg Wikipedia Entry

James Chadwick

Born on October 20, 1891, James Chadwick won the Nobel Prize in Physics in 1935 for his discovery of the neutron.

In 1932 Chadwick discovered a nuclear particle that did not have any charge (one of his letters announcing the discovery can be found here). These chargeless particles, called neutrons, differ from the previously discovered protons in that they do not have any charge. Because they do not have any charge they can be combined with other nuclei without having to overcome electrostatic repulsion.

Atomic nuclei are composed of two different types of particles, protons and neutrons. They both have about the same mass (neutrons are slightly more massive than protons) but differ in the amount of electrostatic charge they carry. Protons carry a positive charge and neutrons have no charge. Because they are all positively charged protons repel each other and therefore it is difficult to add alpha particles (alpha particles have two protons) to a nucleus. A neutron has no charge and can be used to bombard a nucleus without having to overcome the electrostatic charge.

Chadwick also discovered that atomic number is determined by the number of protons that are found in a nucleus. This is now the definition of atomic number. What element a particular atom is is determined by the number of protons present in its nucleus. For example, 1 proton is hydrogen, two protons is helium, three protons is lithium, etc. A full list of atom:atomic number corespondences can be found on a periodic table.

Chadwick later work with particle accelerators contributed to the making of the atomic fission bomb.

For discovering the neutron James Chadwick is the Dead Scientist of the Week for the week of October 18-24, 2009.

References:

James Chadwick Wikipedia entry

James Chadwick Nobel biography

James Chadwick Answers. com biography

Niels Bohr

Born on October 7, 1885, Niels Bohr won the Nobel Prize in physics in 1922 for proposing a structure for the atom and his work in quantum mechanics.

Before Bohr physicists knew that the structure of an atom consisted of a small dense nucleus orbited by electrons. Earnest Rutherford in 1911 published the results of an experiment in which alpha particles emitted by the decay of radium were used to bombard a thin piece of gold foil. The results of the experiment showed that a small amount of the alpha particles were deflected and did not penetrate the gold foil. Rutherford hypothesized that these alpha particles were deflected by the small, hard nuclei of the gold atoms. This led him to propose that atoms were composed of small nuclei surrounded by orbiting electrons that orbited the nuclei in a similar manner to the way planets orbit stars. This model is sometimes called the planetary model (wikipedia entry).

In 1913 Niels Bohr proposed a model for atomic structure where:

1. Electrons orbit nuclei only in certain orbits: orbits set at discrete distances from the nucleus.

2. Electrons can change orbitals, but in doing so they must either absorb (when moving to a higher orbital, further from the nucleus) or emit energy (when moving to a lower orbital, closer to the nucleus).

3. The frequency of the light emitted by an electron changing orbitals is related to the period of the orbital.

The emission of light by electrons falling back into lower orbitals can be seen in neon lights. A gas, sealed in a tube is electrified, causing electrons (normally staying in the lowest energy levels) to move to higher energy levels (higher orbits). When they fall back to their lower, ground state they emit light. This is how neon lights work, and each gas emits a different spectrum giving each gas a distinct color.

For his work determining the structure of atoms, Neils Bohr is our Dead Scientist of the Week for the week of October 4-10, 2009.

References:

Neils Bohr Wikipedia Entry

Bohr Model, Wikipedia Entry

Carpi, Anthony, Vision Learning, Atomic Structure II