Niels Bohr

Niels Bohr
Der dänische Physiker wurde am 7. Oktober 1885 als Sohn eines bekannten Psychologen und einer Bankierstochter in Kopenhagen geboren. Nach seiner Promotion an der dortigen Universität mit einer Arbeit über die Elektronentheorie der Metalle ging er 1911 als Mitarbeiter von Rutherford nach Manchester. Sein Ziel war es, ein Atommodell zu schaffen, das zusätzlich die Linienspektren des Wasserstoffs erklärte und deren Berechnung zuließ. Dies gelang ihm, indem er die Plancksche Quantentheorie mit dem Rutherfordschen Atommodell verband und in Verallgemeinerung dieses Ansatzes die Theorie des periodischen Systems entwickelte.
Bohr starb am 18. November 1962 in Kopenhagen.
http://www.toppoint.de/~cethegus/personen/b/bohr.html

Biographie: Niels Bohr, 1885-1962
1885, 7. Oktober: Niels Bohr wird als Sohn des Physiologieprofessors Christian Bohr und dessen jüdischer Ehefrau Ellen (geb. Adler) in Kopenhagen geboren. Sein jüngerer Bruder entwickelt sich zu einem brillanten Mathematiker.
http://www.dhm.de/lemo/html/biografien/BohrNiels/

Niels Bohr fürchtete deutsche Atomwaffen
Jürgen Langenbach
DER STANDARD, 07. Februar 2002

Veröffentlichte Briefentwürfe nähren alten Verdacht

Kopenhagen/Wien - "Lieber Heisenberg (. . .) Ich erinnere mich sehr gut an unser Gespräch in meinem Zimmer im Institut, wo Sie mir in verschwommenen Worten in einer Art sprachen, die mir nur die feste Überzeugung geben konnte, dass, unter Ihrer Führung, in Deutschland alles getan wird, um Atomwaffen zu entwickeln."

Diese Passage eines Briefentwurfs des dänischen Physikers Niels Bohr an seinen deutschen Kollegen Werner Heisenberg gegen Ende der 50er-Jahre ist das vorläufig letzte Wort zu einer der größten Kontroversen der Wissenschaftsgeschichte, ob nämlich die deutschen Physiker während des Krieges an der deutschen Atombombe bauten.
http://derstandard.at/standard.asp?page=archshow&artfn=/Archiv/20020207/145.HTM

Release of documents relating to 1941 Bohr-Heisenberg meeting
Niels Bohr Archive - nba@nbi.dk
The family of Niels Bohr has decided to release all documents deposited at the Niels Bohr Archive, either written or dictated by Niels Bohr, pertaining specifically to the meeting between Bohr and Heisenberg in September 1941. There are in all eleven documents. The decision has been made in order to avoid possible misunderstandings regarding the contents of the documents.
http://www.nbi.dk/NBA/webpage.html

Niels Bohr - Danish Physicist
Niels Bohr was born on October 7, 1885 in Copenhagen, Denmark. Bohr made numerous contributions to our understanding of atomic structure and quantum mechanics. He won the 1922 Nobel Prize for physics, chiefly for his work on the structure of atoms.
In 1913 Bohr published a theory about the structure of the atom based on an earlier theory of Rutherford's. Rutherford had shown that the atom consisted of a positively charged nucleus, with negatively charged electrons in orbit around it. Bohr expanded upon this theory by proposing that electrons travel only in certain successively larger orbits. He suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties. Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light. Later other physicists expanded his theory into quantum mechanics. This theory explains the structure and actions of complex atoms.
http://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.html

Bohr Atomic Model
In 1913 Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus. The motion of the electrons in the Rutherford model was unstable because, according to classical mechanics and electromagnetic theory, any charged particle moving on a curved path emits electromagnetic radiation; thus, the electrons would lose energy and spiral into the nucleus. To remedy the stability problem, Bohr modified the Rutherford model by requiring that the electrons move in orbits of fixed size and energy. The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.
Using Planck's constant, Bohr obtained an accurate formula for the energy levels of the hydrogen atom. He postulated that the angular momentum of the electron is quantized--i.e., it can have only discrete values. He assumed that otherwise electrons obey the laws of classical mechanics by traveling around the nucleus in circular orbits. Because of the quantization, the electron orbits have fixed sizes and energies. The orbits are labeled by an integer, the quantum number n.
http://zebu.uoregon.edu/~js/glossary/bohr_atom.html

Niels Bohr
Niels Bohr (1885-1962) was the first to propose the quantum theory for the atom. Inside the tiny world of an atom, there are specific energy levels that an electron may have. It can be in 1, 2, or 3, but never in between. We say this kind of energy structure is quantizied.
http://scitech.mus.il.us/science/atomdir/sign3.html

A Science Odyssey: People and Discoveries: Niels Bohr
Niels Bohr was born and educated in Copenhagen, Denmark. He lived, worked, and died there, too. But his mark on science and history was worldwide.
Bohr began to work on the problem of the atom's structure. Ernest Rutherford had recently suggested the atom had a miniature, dense nucleus surrounded by a cloud of nearly weightless electrons. There were a few problems with the model, however. For example, according to classical physics, the electrons orbiting the nucleus should lose energy until they spiral down into the center, collapsing the atom. Bohr proposed adding to the model the new idea of quanta put forth by Max Planck in 1901. That way, electrons existed at set levels of energy, that is, at fixed distances from the nucleus. If the atom absorbed energy, the electron jumped to a level further from the nucleus; if it radiated energy, it fell to a level closer to the nucleus. His model was a huge leap forward in making theory fit the experimental evidence that other physicists had found over the years. A few inaccuracies remained to be ironed out by others over the next few years, but his essential idea was proved correct. He received the Nobel Prize for this work in 1922.
http://www.pbs.org/wgbh/aso/databank/entries/bpbohr.html

Biography of N. H. D. Bohr
Niels Henrik David Bohr was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. Niels, together with his younger brother Harald (the future Professor in Mathematics), grew up in an atmosphere most favourable to the development of his genius.
In the spring of 1912 he was at work in Professor Rutherford's laboratory in Manchester, where just in those years such an intensive scientific life and activity prevailed as a consequence of that investigator's fundamental inquiries into the radioactive phenomena. Having there carried out a theoretical piece of work on the absorption of alpha rays which was published in the Philosophical Magazine, 1913, he passed on to a study of the structure of atoms on the basis of Rutherford's discovery of the atomic nucleus. By introducing conceptions borrowed from the Quantum Theory as established by Planck, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg's ideas in 1925), still fitly serves as an elucidation of the physical and chemical properties of the elements.
http://www.nobel.se/laureates/physics-1922-1-bio.html

Niels Bohr Nobel Prize Physics 1922
"for his services in the investigation of the structure of atoms and of the radiation emanating from them"
http://www.nobel.se/laureates/physics-1922.html

Niels Bohr Winner of the 1922 Nobel Prize in Physics
1922 Nobel Laureate in Physics for his services in the investigation of the structure of atoms and of the radiation emanating from them.
http://www.almaz.com/nobel/physics/1922a.html

Niels Bohr
Ernest Rutherford's model of the atom, developed at the turn of the century, pictured negatively charged electrons moving in circular orbits about a positively charged nucleus. Contradictory to electrodynamic theory the electrons did not emit electromagnetic radiation. Niels Bohr provided the explanation by incorporating Max Planck's quantum theory into Rutherford's atomic model. He envisioned specific discrete energy levels (i.e., shells) for the electrons within which they could move yet not emit radiation. Only if the electrons dropped to a lower energy level, or were raised to a higher level, would they emit or absorb electromagnetic radiation. That the energy of the emitted or absorbed radiation must equal the difference between the original and final energy levels of the electrons explained why atoms only absorb certain wavelengths of radiation. To Albert Einstein, Bohr's achievements were "the highest form of musicality in the sphere of thought". In recognition, Bohr received the Nobel Prize in physics in 1922.
http://www.orcbs.msu.edu/radiation/radhistory/nielsbohr.html

Biographies - Niels Bohr
Niels Bohr was born in Copenhagen, Denmark on October 7, 1885. His scientific interest and talent was evident early on and were encouraged by his parents. After receiving his doctorate, Bohr would later move on to working with J. J. Thomson and Ernest Rutherford which would lead to one of his major discoveries. Bohr was one of the first to see the significance of the atomic number and he would combine the quantum theory with the concept of the atom proposing that radiation was only emitted when an electron jumped from one quantum orbit to the next one. In 1922, he would win the nobel prize for physics.
http://grotto.virtualave.net/bios/bohr.html

Niels Bohr
Niels Bohr (1885 - 1962) was a young post-doctoral fellow from Denmark working with Ernest Rutherford in England during these heady days of discovery. The experimental feature plaguing their minds was the structure of the atom. How could the electrons orbit the nucleus and not lose energy? Why was this configuration stable?
http://www.chembio.uoguelph.ca/educmat/chm386/rudiment/tourquan/bohr.htm

The Bohr Model
The first successful model of hydrogen was developed by Bohr in 1913, and incorporated the new ideas of quantum theory. The major success of this model was an explanation of the simple formula for the emission spectra. The arguments begin with considering the electron orbiting around the proton, as in the planetary model.
http://theory.uwinnipeg.ca/physics/bohr/node3.html

Bohr Model
Niels Bohr proposed a model for the hydrogen atom that explained the spectrum of the hydrogen atom. The Bohr model was based on the following assumptions.

• The electron in a hydrogen atom travels around the nucleus in a circular orbit.
• The energy of the electron in an orbit is proportional to its distance from the nucleus. The further the electron is from the nucleus, the more energy it has.
• As long as the electron stays in a stationary orbit (same distance from the nucleus), it does not emit radiation as classical physics required.
• Only a limited number of orbits with certain energies are allowed. This is the quantization of orbits using Planck's hypothesis. Allowed orbits have their electron's angular momentum be an integral multiple of Planck's constant divided by 2pi.
• An electron can only pass from one stationary state to another. Radiation is absorbed when an electron jumps to a higher energy orbit and emitted when an electron falls into a lower energy orbit.
• The energy of the radiation emitted or absorbed is exactly equal to the difference between the energies of the orbits.

http://erkki.kennesaw.edu/~lcombs/genchem7/ge00003.htm

Niels Bohr - On the Spectrum of Hydrogen
Niels Bohr
Hydrogen possesses not only the smallest atomic weight of all the elements, but it also occupies a peculiar position both with regard to its physical and its chemical properties. One of the points where this becomes particularly apparent is the hydrogen line spectrum.
The spectrum of hydrogen observed in an ordinary Geissler tube consists of a series of lines, the strongest of which lies at the red end of the spectrum, while the others extend out into the ultra-violet, the distance between the various lines, as well as their intensities, constantly decreasing. In the ultraviolet the series converges to a limit. ...
Let us now assume that a hydrogen atom simply consists of an electron revolving around a nucleus of equal and opposite charge, and of a mass which is very large in comparison with that of the electron. It is evident that this assumption may explain the peculiar position already referred to which hydrogen occupies among the elements, but it appears at the outset completely hopeless to attempt to explain anything at all of the special properties of hydrogen, still less its line spectrum, on the basis of considerations relating to such a simple system.For this it will be necessary to assume that the orbit of the electron cannot take on all values, and in any event the line spectrum clearly indicates that the oscillations of the electron cannot vary continuously between limits. The impossibility of making any progress with a simple system like the one considered here might have been foretold from a consideration of the dimensions involved. It can be seen that it is impossible to employ Rutherford's atomic model so long as we confine ourselves exclusively to the ordinary electrodynamics.
Let us now try to overcome these difficulties by applying Planck's theory to the problem.
http://maple.lemoyne.edu/~giunta/bohr.html

Niels Bohr (1885-1962) & Creative Quotations:
"When it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images."
http://www.bemorecreative.com/one/323.htm

Bohr, Niels (1885-1962)
Danish physicist who proposed a successful quantum model of the atom in 1913. His model assumed that (1) the Electron exists at precise distances from the nucleus, (2) as long as an Electron remains in one location, no energy is given off, (3) Electrons have circular orbits (this is only correct for s orbitals), and (4) the angular momenta associated with allowed electron motion are integral multiples of h.
http://www.treasure-troves.com/bios/BohrNiels.html

Bohr, Niels
Born: 7 Oct 1885 in Copenhagen, Denmark
Died: 18 Nov 1962 in Copenhagen, Denmark
Bohr is best known for the investigations of atomic structure referred to above and also for work on radiation, which won him the 1922 Nobel Prize for physics. He said in 1923:

Notwithstanding the fundamental departure from the ideas of the classical theories of mechanics and electrodynamics involved in these postulates, it has been possible to trace a connection between the radiation emitted by the atom and the motion of the particles which exhibits a far-reaching analogy to that claimed by the classical ideas of the origin of radiation.

It was Bohr's view of quantum theory which was eventually to become accepted. Einstein expressed grave doubts about Bohr's interpretation and Bohr, Einstein and Ehrenfest spent many hours in deep discussion, but Bohr's view prevailed. Bohr expressed this view saying:

Evidence obtained under different experimental conditions cannot be comprehended within a single picture, but must be regarded as complementary in the sense that only the totality of the phenomena exhausts the possible information about the objects.

Bohr's other major contributions, in addition to quantum theory, include his theoretical description of the periodic table of elements around 1920, his theory of the atomic nucleus being a compound structure in 1936, and his understanding of uranium fission in terms of the isotope 235 in 1939.
http://www.vma.bme.hu/mathhist/Mathematicians/Bohr_Niels.html

Niels Bohr
Niels Bohr was a Danish physicist who lived between 1885-1962. He investigated atomic structure, modifying Rutherford's old model of an atom. Bohr also claimed that an atom's chemical properties are determined only by the electrons with the largest orbits.
http://www.windows.umich.edu/cgi-bin/tour_def/people/modern_era/bohr.html

Niels Bohr
One of the most sparkling and prolonged scientific jousting matches took place between Niels Bohr and Albert Einstein in the 20s and 30s. The latter, who could never accept the probabilistic nature of quantum mechanics, produced a series of gedanken experiments (thought experiments) designed to disprove the new theory. Bohr would then attempt to show where Einstein had gone wrong. In one of Bohr's successful attempts at this, he was especially pleased to note that Einstein had forgotten that according to his own theory of general relativity clocks run more slowly under the influence of a gravitational field.
http://orac.sunderland.ac.uk/~hs0bcl/h_nb.htm

Discussions with Einstein on Epistemological Problems in Atomic Physics
Niels Bohr
From the very beginning the main point under debate has been the attitude to take to the departure from customary principles of natural philosophy characteristic of the novel development of physics which was initiated in the first year of this century by Planck's discovery of the universal quantum of action. This discovery, which revealed a feature of atomicity in the laws of nature going far beyond the old doctrine of the limited divisibility of matter, has indeed taught us that the classical theories of physics are idealisations which can be unambiguously applied only in the limit where all actions involved are large compared with the quantum. The question at issue has been whether the renunciation of a causal mode of description of atomic processes involved in the endeavours to cope with the situation should be regarded as a temporary departure from ideals to be ultimately revived or whether we are faced with an irrevocable step towards obtaining the proper harmony between analysis and synthesis of physical phenomena. To describe the background of our discussions and to bring out as clearly as possible the arguments for the contrasting viewpoints, I have felt it necessary to go to a certain length in recalling some main features of the development to which Einstein himself has contributed so decisively.
http://www.marxists.org/reference/subject/philosophy/works/bohr.htm

Einsteins's Reply to Criticisms in relation to Epistemological Problems in Atomic Physics
Albert Einstein
I now come to what is probably the most interesting subject which absolutely must be discussed in connection with the detailed arguments of my highly esteemed colleagues Born, Pauli, Heitler, Bohr, and Margenau. They are all firmly convinced that the riddle of the double nature of all corpuscles (corpuscular and undulatory character) has in essence found its final solution in the statistical quantum theory. On the strength of the successes of this theory they consider it proved that a theoretically complete description of a system can, in essence, involve only statistical assertions concerning the measurable quantities of this system. They are apparently all of the opinion that Heisenberg's indeterminacy-relation (the correctness of which is, from my own point of view, rightfully regarded as finally demonstrated) is essentially prejudicial in favour of the character of all thinkable reasonable physical theories in the mentioned sense. In what follows I wish to adduce reasons which keep me from falling in line with the opinion of almost all contemporary theoretical physicists. I am, in fact, firmly convinced that the essentially statistical character of contemporary quantum theory is solely to be ascribed to the fact that this [theory] operates with an incomplete description of physical systems.
http://www.marxists.org/reference/subject/philosophy/works/einstein.htm

Niels Bohr
Links zu Websites über Niels Bohr.
http://www.jteln.de/privat/p_niester/p_natwis/niels_bohr/

AITLC Guide to Niels Bohr
Links zu Websites über Niels Bohr.
http://tlc.ai.org/bohr.htm

Bohr
Bohr had studied under Rutherford, the scientists that proposed the idea that electrons travelled like planets around the nucleus. There was, however a problem with Rutherford's atomic model. The fundamental problem with Rutherford's model was the continual loss of energy by the electrons, causing them to spiral down into the nucleus. In 1913, the problems of the Rutherford Model was solved by Bohr. According to Bohr, the electrons in atoms cannot exist in arbitrary orbits. Instead they are found only in certain "states".
http://plaza.v-wave.com/atomicphysics/bohr.htm

Bohr
Bohr's theory of atomic structure, for which he received the Nobel Prize in physics in 1922, was published in papers between 1913 and 1915. His work drew on Rutherford's nuclear model of the atom, in which the atom is seen as a compact nucleus surrounded by a swarm of much lighter electrons. Bohr's atomic model made use of quantum theory and the Planck constant (the ratio between quantum size and radiation frequency). The model suggested that an atom emits electromagnetic radiation only when an electron in the atom jumps from one quantum level to another. This model contributed enormously to future developments of theoretical atomic physics.
http://www.newlisbon.k12.wi.us/physicists/bohr.html