Niels Janniksen Bjerrum (11 March 1879 in

Copenhagen Copenhagen ( or .; da, København ) is the capital and most populous city of Denmark, with a proper population of around 815.000 in the last quarter of 2022; and some 1.370,000 in the urban area; and the wider Copenhagen metropolitan ar ...

– 30 September 1958) was a

Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish ance ...

chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe th ...

. Niels Bjerrum was the son of ophthalmologist

Jannik Petersen Bjerrum Jannik Petersen Bjerrum (26 December 1851 – 2 July 1920) was a Danish ophthalmologist who was a native of Skærbæk, a town in the southernmost part of Jutland. In 1864 Skærbæk became part of Germany due to consequences of the Second Schlesw ...

, and started to study at

University of Copenhagen The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...

in 1897. He received his Master's degree in 1902 and his Doctor's degree in 1908, and did research in

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

chemistry under

Sophus Mads Jørgensen Sophus Mads Jørgensen (4 July 1837 – 1 April 1914) was a Danish chemist. He is considered one of the founders of coordination chemistry, and is known for the debates which he had with Alfred Werner during 1893-1899. While Jørgensen's theories o ...

. He became a

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in 1912, and in 1914 he became professor of chemistry at the Royal Agricultural College (''Landbohøjskolen'') in Copenhagen, as successor of Odin Tidemand Christensen. He stayed on this post until his retirement in 1949, and from 1939 to 1946 he was also the Director of the College. Importantly, Bjerrum introduced the concept of three forms of molecular energy, translational, vibrational and rotational which was important in understanding vibrational spectroscopy. He is also noted for the theory behind the

Bjerrum length The Bjerrum length (after Danish chemist Niels Bjerrum 1879–1958 ) is the separation at which the electrostatic interaction between two elementary charges is comparable in magnitude to the thermal energy scale, k_\text T, where k_\text is the B ...

, and the

Bjerrum plot A Bjerrum plot (named after Niels Bjerrum; sometimes also known as a Sillén diagram or a Hägg diagram) is a graph of the concentrations of the different species of a polyprotic acid in a solution, as a function of pH, when the solution is at ...

. Bjerrum also performed some of the first research on the measurement of soil acidity. His son Jannik Bjerrum (1909–1992) also became a chemist and was active in the area of complex chemistry.

Contribution to the Bohr Model of the atom

Bjerrum worked with Nernst in Berlin and contributed to chemical physics in four papers (1911–1914). The subject of the papers is the kinetic and quantum theories through absorption measurements in the infrared to elucidate the constitution and the optical and thermal properties of matter. He advanced the studies of

specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...

that had been made for solids by

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theory ...

Walther Nernst Walther Hermann Nernst (; 25 June 1864 – 18 November 1941) was a German chemist known for his work in thermodynamics, physical chemistry, electrochemistry, and solid state physics. His formulation of the Nernst heat theorem helped pave the wa ...

, and Lindemann. He showed the connection of specific heats and the spectrum as required by the quantum theory. Using the quantum hypothesis, the infrared absorption spectra of water vapor were shown to link to the line broadening caused by molecular rotational frequencies that vary discontinuously and to radiating atoms that do not rotate. This phenomenon was mentioned by Niels Bohr as contributing greatly to his 1913 model of the

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...

because it provided agreement with specific heat investigations which suggested that the rotational energy of atoms must be very small.

Contribution to electrolytes theory

Between 1916 and 1926 he investigated the properties of electrolytic solutions in regards to their dissociation and

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in German journals like

Z. anorg. allgem. Chem. Z is the 26th and last letter of the Latin alphabet. Z may also refer to: Film and television * Z (1969 film), ''Z'' (1969 film), a 1969 Algerian-French thriller film based on the murder of a Greek politician. * Z (1999 film), ''Z'' (1999 film) ...

(1918, 1920) and Ergebnisse der exakten Naturwissenschaften (1926). He also published in the British journal

Transactions of the Faraday Society The ''Journal of the Chemical Society, Faraday Transactions'' was a peer-reviewed scientific journal published from 1905 until 1998. The journal was originally published by the Faraday Society under the name ''Transactions of the Faraday Society'' ...

(1927). He introduced the quantity osmotic coefficient in relation to non-

ideal solution In chemistry, an ideal solution or ideal mixture is a solution that exhibits thermodynamic properties analogous to those of a mixture of ideal gases. The enthalpy of mixing is zero as is the volume change on mixing by definition; the closer to zero ...

s of electrolytes.

Contribution to the Bohr Model of the atom

Contribution to electrolytes theory

See also

References

Further reading