History of Chemistry
This page provides information about the historical development of models of the atom. Chemistry 1105 students can provide substantive contributions to this page in order to earn Outcome 16. Alternatively, Chem 1105 students can earn this outcome by mastering the multiple choice exam questions associated with Outcome 16.
For each historical person listed below, please add the year or years during which important work was accomplished, a clear statement of their research result (or theoretical contribution) and its significance, and a concise description of the experiment that led to the result. In some cases, an important mathematical equation or formula may also be included.
Each piece of information should be clearly referenced. All reference citations, including web citations, should be complete (as you learned to do with Outcome 42.) If the reference is to a web site, a link should be added to the wiki page that takes the reader directly to the web site. See Help link in left menu bar on this page for wiki editing assistance.
All edits you make to this page are recorded in the page history (see tabs at top of page). You will need to log in (upper left corner of page) with your campus uca and password in order to edit the page.
He is a co-originator of the belief that all matter is made up of various imperishable, indivisible elements which he called "atomos" ("atoma" plural) or "indivisible units". This is where we get the English term "atom". His theory argued that atoms only had several properties which include size, shape, and weight. Other properties, such as color and taste, are the result of interactions between the atoms in our bodies and the atoms of the matter that we are dealing with.
Reference: "Democritus." Wikipedia-The Free Encyclopedia. 2 Oct 2008 <[]>.
He coined the term that eventually became "atom" in 450 BC.
Reference: "Atom." Wikipedia-The Free Ecyclopedia. 2 Oct 2008 <[]>.
Democritus lived to around that age of 90. Having been born in Abdera around 459 BCE this was an exceptionally long life for a man of his times. This could be attributed to both his love of happiness and also to his rational logic that he applied to all things in life. In addition to his early theory of the atom (which was at the time philosophy) Democritus was very involved in other activities, from plays and psychology to government and engineering. He has many wise proverbs that still ring true toady, such as "The hopes of right-thinking men are attainable, but those of the unintelligent are impossible."
Reference: "Democritus" -- History of Psychology 16 Dec 2008 <[]>.
Democritus was a strict determinist that believed everything resulted from natural laws. He followed in the footsteps of Leucippus, who he had a lot in common with and carried on the scientific rationalist psychology of their city. He was an atomist, meaning he tried to explain the world without reasoning. He wanted questions answered with a mechanistic explanation and wanted mechanistic answers. Now, modern scientists have answered the questions in the same way and have led to scientific knowledge of in physics.
Reference: "Democritus" -- Philosophy and science 29 Sep 2012 <htp://en.wikipedia.org/wiki/Democritus>.
Democritus was the first person to use the term "atomos." He named the atom after the Greek word atomos, which mean 'that which can't be split.'
Reference: Kross, Brian. "Questions and Answers - Where Does the Word Atom Come from and Who First Used This Word?" Questions and Answers - Where Does the Word Atom Come from and Who First Used This Word? Jefferson Lab, n.d. Web. 09 Dec. 2013. <http://education.jlab.org/qa/history_01.html>.
John Dalton was born on September 6 1766 and died July 27 1844. He was an English chemist, meteorologist and physicist. His best known work is the development of the atomic theory and his research into colour blindness. Dalton published many papers about his idea on the absorption of gases by water and other liquids. These contained his law of partial pressures now known as Dalton's law. He was also one of the earliest workers in volumetric analysis.
John Dalton enunciated Gay-Lussac's law or Charles's law, published in 1802. In the years following the reading of those essays, Dalton published several papers on similar topics, that on the absorption of gases by water and other liquids (1803). This contained his law of partial pressures now known as Dalton's law.
A study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & Phil, concluded that so far from Dalton being led by his search for an explanation of the law of multiple proportions to the idea that chemical combination consists in the interaction of atoms of definite and characteristic weight, the idea of atoms arose in his mind as a purely physical concept, forced upon him by study of the physical properties of the atmosphere and other gases.
John Dalton came up with his own Atomic Theory. It had five main points which included: (1) Elements are made of tiny particles called atoms. (2) All atoms of a given atom are identical. (3) The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative weights. (4) Atoms of one element can combine with atoms of another element to form chemical compounds; a given compound always has the same relative numbers of types of atoms. (5) Atoms cannot be created, divided into smaller particles; nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.
Reference: "John Dalton." Wikipedia, the free encyclopedia 4 Oct 2008. <http://en.wikipedia.org/wiki/John_Dalton>
"John Dalton." "Wikipedia, the free encyclopedia" 27 Sep 2011. http://en.wikipedia.org/wiki/John_Dalton#Gas_laws
Dmitri Mendeleev was born in Siberia in 1834 and died in 1907. He began to study science in St. Petersburg and graduated in 1856. Mendeleev is best known for creating one of the first periodic tables. He took the 63 known elements (at the time) and arranged them according to atomic weight. He also arranged them by their similarities of properties. Dmitri Mendeleev's first Periodic Table of the Elements was published in Principles of Science. When he created his table, he left spaces for elements to be added and predicted future elements. His table did not include any of the Noble Gases we have today because they were not discovered at the time. A guy named Moseley modified and corrected Mendeleev's periodic table many times throughout the years. Mendeleev is also known for studying the thermal expansion of liquids and for studying the nature and origin of petroleum. References: "Who was Dmitri Mendeleev?." Kiwi Web, Chemistry and New Zealand. 1998. 7 Oct 2008 <http://www.chemistry.co.nz/mendeleev.htm>.
J. J. Thompson
J.J. Thompson was credited for the discovery of electrons in 1897.
Reference: "Electron." Wikipedia-The Free Encyclopedia.2 Oct 2008 <[]>.
Thompson conducted a series of experiments involving cathode rays and cathode ray tubes that led him to his discovery. The three experiments are explained below:
Experiment 1: He constructed a cathode ray tube ending in a pair of cylinders with slits in them. The slits were connected to an electrometer. He found that if the rays were bent so that they could not enter the slits, the electrometer would register a very small charge. Concluded that the negative charge was inseparable from the rays.
Experiment 2: He constructed a cathode ray tube with an almost perfect vacuum and coated one end with phosphorescent paint. He found that rays did indeed bend with the influence of an electric field, and it was in a way that indicated a negative charge.
Experiment 3: He measured the mass to charge ratio of cathode rays by measuring how much they were deflected by magnetic fields and how much energy they carried. Concluded that cathode rays were made of particles and called them "corpuscles." The "corpuscles" came from within the atoms of the electrodes. The "corpuscles" that he discovered are identified with the electron which was proposed by G. Johnstone Stoney.
Reference: "J.J. Thompson." Wikipedia-The Free Encyclopedia. 2 Oct 2008 <[]>.
Mass to change ratio
In the 19th century the mass-to-charge ratios of some ions were measured by electrochemical methods. In 1897 the mass-to-charge ratio, [m⁄e], of the electron was first measured by J. J. Thomson. By doing this he showed that the electron—postulated earlier to explain electricity—was in fact a particle with a mass and a charge; and that its mass-to-charge ratio was much smaller than that of the hydrogen ion H+.In 1898 Wilhelm Wien separated ions (canal rays) according to their mass-to-charge ratio with an ion optical device with superimposed electric and magnetic fields (Wien filter). In 1901 Walter Kaufman measured the relativistic mass increase of fast electrons. In 1913, Thomson measured the mass-to-charge ratio of ions with an instrument he called a parabola spectrograph. Today, an instrument that measures the mass-to-charge ratio of charged particles is called a mass spectrometer.
Thomson's experiments and big idea:
Thomson built a cathode ray tube. It was connected to an electrometer, a device for catching and measuring electrical charge. Thomson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. As Thomson saw it, the negative charge and the cathode rays must somehow be stuck together: you cannot separate the charge from the rays.
He calculated the ratio of the mass of a particle to its electric charge (m/e). He collected data using a variety of tubes and using different gases.
He later announced: ""we have in the cathode rays matter in a new state, a state in which the subdivision of matter is carried very much further than in the ordinary gaseous state: a state in which all matter... is of one and the same kind; this matter being the substance from which all the chemical elements are built up."
Reference: "Three Experiments and One Big Idea." Three Experiments and One Big Idea. American Institute of Physics, n.d. Web. 08 Dec. 2013. <http://www.aip.org/history/electron/jj1897.htm>.
Ernest Rutherford was the second son born into a family of twelve children on August 30, 1871. His father, James Rutherford, was a Scottish wheelwright. His mother, Martha Thompson, was an English schoolteacher. Growing up, Ernest’s primary education was received at government institutions. When he turned sixteen, he began his secondary education at Nelson Collegiate School. From here, Ernest received a scholarship and moved on to the University of New Zealand, Wellington where he attended Canterbury College. Rutherford received his M.A. in 1893 with a double major in both Mathematics, and Physical Science. His research in New Zealand was focused on the “magnetic properties of iron exposed to high-frequency oscillations." (Nobel Lectures) His thesis Magnetization of Iron by High-Frequency Discharges included an original experiment. His subsequent paper, Magnetic Viscosity, contained descriptions of a highly accurate highly precise device for measuring time down to the hundred-thousandth of a second. This idea produced in 1896 was well ahead of its time.
The post-graduate continued his research at Canterbury College until he received his B.Sc. in 1894. This same year, Rutherford was awarded another scholarship to attend Trinity College, Cambridge. He then became a research student under J.J. Thompson, a fellow Nobel Prize winner. Rutherford was almost immediately taken under J.J. Thompson’s wing in the laboratory. He then created a detector capable of locating electromagnetic waves. From here, Rutherford began collaborating with Thompson on experiments. Together, they studied how ions acted in gases that were treated with x-rays. In 1897, Rutherford received yet another degree, this one, a B.A. in research from Trinity College.
References: From Nobel Lectures, Chemistry 1901-1921, Elsevier Publishing Company, Amsterdam, 1966 <http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html>
Ernest Rutherford published the atomic theory in 1911, which states that the atom has a central, positive nucleus that is surrounded by negative electrons that orbit around the nucleus. Rutherford's model suggests that most of the atom's mass is included in the small nucleus, and the rest of the atom is nearly empty space. Rutherford established this model when conducting his gold foil experiment. Rutherford disproved the plum pudding model of the atom. Radioactive particles were fired through thin gold foil and were detected by screens coated with zinc sulfide. Rutherford concluded that although most of the particles passed right through the foil, some particles, nearly 1 in 8000, were deflected. Reference: Rutherford - Atomic Theory. Chemsoc Timeline. 8 Oct 2008. <http://www.rsc.org/chemsoc/timeline//pages/1911.html>
Ernest Rutherford received an Exhibition Science Scholarship at Trinity College in Cambridge in 1851. At this time he studied under J.J. Thomson. In 1898 Ernest Rutherford discovered the existence of alpha and beta rays in Uranium radiation. Following this he discovered a new noble gas, thoron, which is an isotope of radon. His experiments on radioactive bodies and alpha rays took place in Montreal at McGill, in the Macdonald Laboratory. Reference: "Ernest Rutherford-biography" nobelprize.org 13 Dec 2011. <http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html>
Hans Geiger and Ernest Marsden
Hans Geiger best known as the co-inventor of the Geiger counter and for the Geiger-Marsden experiment which discovered the atomic nucleus.
In 1902 Geiger started studying physics and mathematics in University of Erlangen. In 1909, he and Ernest Marsden conducted the famous Geiger-Marsden experiment called the gold foil experiment. Together they created the Geiger counter. In 1911, Geiger and John Mitchell Nuttall discovered the Geiger-Nuttall law (or rule), which led to Rutherford's atomic model. In 1928 Geiger and his student Walther Müller created an improved version of the Geiger counter, the Geiger-Müller counter. http://en.wikipedia.org/wiki/Hans_Geiger
On the other hand, Ernest Marsden, who studied at the University of Manchester under Ernest Rutherford and Hans Geiger,contributed to Ernest Rutherford's work on the structure of the atom. Durning the 1900's, Marsden's work consisted of observing that a tiny fraction of alpha particles fires at a thin gold foil were deflected straight back, in which Rutherford used these results to determine a new structure of the atom. (1) Also, Marsden and Geiger continued their study with alpha particles and later, an 1913, correlated the nuclear charge with the atomic number. (2)
Hans Geiger and Ernest Marsden discovered that the nucleus of an atom accounts for most of the atom's mass, but very little of its size. An atom is mostly empty space with a small, dense nucleus.
In 1909, Robert Millikan created an experiment that would allow him to measure an electron's charge. In the experiment, a fine spray of oil was squirted above a pair of metal plates (the top of the two had a small hole). As the mist settled, some of the oil dripped into the hole and in the empty space between the plates. Millikan would illuminate these drops with X-rays, taking electrons off molecules in the air; these electrons then attached themselves to the oil, giving the drops an electrical charge. By measuring how fast the drops fell when the metal plates were charged and when they were not, Millikan could determine the charge that each drop possessed. After reviewing his results, Robert found that all of the values he obtained were whole-number multiples of -1.60 × 10-19 C. Since a drop of oil can logically only attach to a whole number of electrons, that value is carried by each electron. Once Millikan had measured the electron's charge, he then found the mass using J. J. Thomson's charge-to-mass ratio. The mass was determined to be 9.09 × 10-28 g. Since this experiment other scientists have found the more accurate mass of the electron to be 9.109383 × 10-28 g.
James, Brady. Chemistry Matter and Its Changes. 5th Edition. New York: John Wiley & Sons Inc.
Neil Bohr first started experiments under J.J. Thomson and he later went to study under Ernest Rutherford. After studying and experimenting with Rutherford, Neil Bohr published his model of atomic structure in 1913 which introduced the theory of electrons traveling in orbits around the atom's nucleus and the chemical properties of the element being largely determined by the number of electrons in the outer orbits. Neil Bohr also introduced the idea that an electron could drop from a higher-energy orbit down to a lower energy-orbit, emitting a photon of discrete energy. This idea became the basis of the quantum theory.
Neil Bohr contributed to chemistry and physics in the following ways: Bohrs model-the theory that electrons travel in discrete orbits around the atom's nucleus, the shell model of atom-where the chemical properties of an element are determined by the electrons in the outermost orbit, the correspondence principle-the basic tool of the old quantum theory, the liquid drop model of the atomic nucleus, identified the isotope of uranium that was responsible for slow-neutron fission, much work on the Copenhagen interpretation of quantum mechanics, and the principle of complementary-that items could be separately analyzed as having several contradictory properties.
Bohr also conceived the principle of complementarity: that items could be separately analyzed as having several contradictory properties. For example, physicists currently conclude that light behaves either as a wave or a stream of particles depending on the experimental framework — two apparently mutually exclusive properties — on the basis of this principle. reference: http://en.wikipedia.org/wiki/Niels_Bohr
The Bohr model, devised by Niels Bohr, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. This was an improvement on the earlier cubic model (1902), the plum-pudding model (1904), the Saturnian model (1904), and the Rutherford model (1911). Since the Bohr model is a quantum physics-based modification of the Rutherford model, many sources combine the two, referring to the Rutherford–Bohr model. reference: http://en.wikipedia.org/wiki/Bohr_model
James Chadwick was born in Bollington, Cheshire, the son of John Joseph Chadwick and Anne Mary Knowles. He went to Bollington Cross C of E Primary School, attended Manchester High School, and studied at the Universities of Manchester and Cambridge. In 1913 Chadwick went and worked with Hans Geiger at the Technical University of Berlin. He also worked with Ernest Rutherford. He was in Germany at the start of World War I and would be interned in Ruhleben P.O.W. Camp just outside Berlin. During his internment he had the freedom to set up a laboratory in the stables. With the help of Charles Ellis he worked on the ionization of phosphorus and also on the photo-chemical reaction of carbon monoxide and chlorine. He spent most of the war years in Ruhleben until Geiger's laboratory interceded for his release.
In 1932 Chadwick made a fundamental discovery in the domain of nuclear science: he discovered the particle in the nucleus of an atom that became known as the neutron because it has no electric charge. In contrast with the helium nuclei (alpha particles) which are positively charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any Coulomb barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements. In this way, Chadwick prepared the way towards the fission of uranium 235. For this important discovery he was awarded the Hughes Medal of the Royal Society in 1932, and subsequently the Nobel Prize for Physics in 1935.
Chadwick’s discovery made it possible to create elements heavier than uranium in the laboratory. His discovery particularly inspired Enrico Fermi, Italian physicist and Nobel laureate, to discover nuclear reactions brought by slowed neutrons, and led Otto Hahn and Fritz Strassmann, German radiochemists in Berlin, to the revolutionary discovery of “nuclear fission”.
Chadwick became professor of physics at Liverpool University in 1935. As a result of the Frisch-Peierls memorandum in 1940 on the feasibility of an atomic bomb, he was appointed to the MAUD Committee that investigated the matter further. He visited North America as part of the Tizard Mission in 1940 to collaborate with the Americans and Canadians on nuclear research. Returning to England in November 1940, he concluded that nothing would emerge from this research until after the war. In December 1940 Franz Simon, who had been commissioned by MAUD, reported that it was possible to separate the isotope uranium-235. Simon's report included cost estimates and technical specifications for a large uranium enrichment plant. James Chadwick later wrote that it was at that time that he "realized that a nuclear bomb was not only possible, it was inevitable. I had then to take sleeping pills. It was the only remedy."
He shortly afterward joined the Manhattan Project in the United States, which developed the atomic bombs dropped on Hiroshima and Nagasaki. Chadwick was knighted in 1945.
Source of Material: http://en.wikipedia.org/wiki/James_Chadwick
>p Wolfgang Pauli, received the Nobel Prize in physics in 1945, for the discovery of the exclusion principle, also called the Pauli Principle. The principle was proposed in 1925 as an assertion that no two electrons in an atom can be at the same time in the state or configuration. This was to account for the observed patterns of light emission from atoms. The exclusion principle subsequently has been generalized to include the whole class of particles called fermions. The Pauli exclusion principle indicates, that only two electrons are allowed in each atomic energy state, leading to the successive buildup of orbitals around the nucleus. This prevents matter from collapsing to an extremely dense state.
1.Gavryushin,& Zukauskas, "Pauli Exclusion Principle." (18 Apr 2002 ). 23 Oct 2008.
2. Massimi, Michela (2005). Pauli's Exclusion Principle. Cambridge University Press. ISBN 0-521-83911-4.
Albert Einstein is known for his theory of relativity and mass–energy equivalence, E = mc².
Einstein has contributed to physics by his special theory of relativity, his general theory of relativity, and a new theory of gravitation. He also contributed to the advances in the fields of relativistic cosmology, capillary action, critical opalescence, classical problems of statistical mechanics and to quantum theory.
Einstein published over 300 scientific works and over 150 non-scientific works. http://en.wikipedia.org/wiki/Albert_Enstein
After Einstein was finished with his theory of relativity his research consisted of attempts to generalize his theory of gravitation. This is because he wanted to unify and simplify the fundamental laws of physics, in particular, gravitation and electromagnetism.
He described the unified field theory in 1950; however, he was never able to successfully unify the laws of physics under a single model. Because Einstein focused his later work on this unsuccessful model, he ignored the mainstream developments within his field that many people believed he could have clarified.
"Albert Einstein." Wikipedia-the Free Encyclopedia. 17 Dec 2008 [].
Einstein attended school at the Luitpold Gymnasium in Munich. When he moved to Italy, he continued his schooling at Aarau, Switzerland. Einstein was trained as a physics and mathematics teacher at the Swiss Federal Polytechnic School in Zurich. He obtained his diploma in 1901, and he finished his doctorate degree in 1905. Einstein’s special theory of relativity came from his attempt to join the laws of mechanics with the laws of the electromagnetic field. His study of the problems with statistical mechanics and the problems of how they merged with the quantum theory is what led to his explanation of the Brownian movement of molecules. Einstein’s observations of thermal properties of light with low radiation density are what laid the foundation for the photon theory of light. Although Einstein is thought of as only a man of science, he was also active in politics. After WWII, he was a leading figure in the World Government Movement and he was also offered the presidency of Israel. Einstein’s works were recognized with awards such as the Copley Medal of the Royal Society of London, and the Franklin Medal of the Franklin Institute.
"Albert Einstein - Biographical." Nobelprize.org. Nobel Media AB 2013. Web. 29 Sep 2013. <http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/einstein-bio.html>
Erwin Rudolf Josef Alexander Schrödinger (12 August 1887 – 4 January 1961) was an Austrian physicist who achieved fame for his contributions to quantum mechanics, especially the Schrödinger equation, for which he received the Nobel Prize in 1933. In 1935, after extensive correspondence with personal friend Albert Einstein, he proposed the Schrödinger's cat thought experiment.
He became the assistant to Max Wien, in Jena, and in September 1920 he attained the position of ao. Prof. (Ausserordentlicher Professor), roughly equivalent to Reader (UK) or associate professor (US), in Stuttgart. In 1921, he became o. Prof. (Ordentlicher Professor, i.e. full professor), in Breslau (now Wrocław, Poland). In 1921, he moved to the University of Zürich. In January 1926, Schrödinger published in the Annalen der Physik the paper "Quantisierung als Eigenwertproblem" [tr. Quantisation as an Eigenvalue Problem] on wave mechanics and what is now known as the Schrödinger equation. In this paper he gave a "derivation" of the wave equation for time independent systems, and showed that it gave the correct energy eigenvalues for the hydrogen-like atom. This paper has been universally celebrated as one of the most important achievements of the twentieth century, and created a revolution in quantum mechanics, and indeed of all physics and chemistry. A second paper was submitted just four weeks later that solved the quantum harmonic oscillator, the rigid rotor and the diatomic molecule, and gives a new derivation of the Schrödinger equation. A third paper in May showed the equivalence of his approach to that of Heisenberg and gave the treatment of the Stark effect. A fourth paper in this most remarkable series showed how to treat problems in which the system changes with time, as in scattering problems. These papers were the central achievement of his career and were at once recognized as having great significance by the physics community.
In 1927, he succeeded Max Planck at the Friedrich Wilhelm University in Berlin. In 1933, however, Schrödinger decided to leave Germany; he disliked the Nazis' anti-semitism. He became a Fellow of Magdalen College at the University of Oxford. Soon after he arrived, he received the Nobel Prize together with Paul Adrien Maurice Dirac. His position at Oxford did not work out; his unconventional personal life (Schrödinger lived with two women) was not met with acceptance. In 1934, Schrödinger lectured at Princeton University; he was offered a permanent position there, but did not accept it. Again, his wish to set up house with his wife and his mistress may have posed a problem. He had the prospect of a position at the University of Edinburgh but visa delays occurred, and in the end he took up a position at the University of Graz in Austria in 1936.
In the midst of these tenure issues in 1935, after extensive correspondence with personal friend Albert Einstein, he proposed the Schrödinger's cat thought experiment
Source of Material- http://en.wikipedia.org/wiki/Erwin_Schrodinger
Louis de Broglie
In 1924, his doctoral thesis in the Research on Quantum Theory introduced the theory of electron waves. This research included the wave-particle duality theory of matter. This theory showed the de Broglie hypothesis, which stated that any moving particle or object had an associated wave. He based this work off of the work of Albert Einstein and Planck. From this research, he created a new branch of physics called wave mechanics. This branch combined the physics of light and matter. Also in the application of his work, he further developed the use of electron microscopes to get much better resolution than optical ones. The reason for this was because of the shorter wavelengths of electrons compared with photon.
Louis de Broglie contributions to chemistry:
-came up with broglie hypothesis in the wave-particle duality theory
-stated any moving particle or object had an associated wave
-created a new branch of chemistry consisting of the physics of light and matter--called wave mechanics
-further developed use of electron microscope
References: “Louis de Broglie.” Wikipedia, the free encyclopedia. 17 Nov 2008. <http://en.wikipedia.org/wiki/Louis_de_Broglie?>
Max Planck was born on April 23, 1858 in Kiel, Germany. He studied at the Universities of Munich and Berlin, and received his doctorate in philosophy at Munich in 1879. He started his work on thermodynamics which he published papers on. Around 1894, he had an interest on the problems of radiation processes. He was led to the problem of the distribution of the energy in the spectrum of full radiation. He observed wavelength distribution and the energy emitted by a black body to deduce the relationship between the energy and the frequency of radiation. In 1990 he announced that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant. Planck's work on quantum theory was published in the Annalen der Physik. He also won the Society's Copley Medal in 1928. He died on October 4, 1947 in Göttingen.
Max Planck:The Nobel Prize in Physics 1918. The Nobel Foundation. 13 October 2008. http://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html
He was born May 1, 1825, Lausanne, Switz. He died March 12, 1898. During his schooling he excelled in mathematics, and so decided to focus on that field when he attended university. He studied at the University of Karlsruhe and the University of Berlin, then completed his Ph.D. from the University of Basel in 1849. Despite being a mathematician, he is not remembered for any work in that field; rather, his major contribution (made at the age of sixty, in 1885) was an empirical formula for the visible spectral lines of the hydrogen atom. Using Ångström's measurements of the hydrogen lines, he arrived at a formula for finding the wavelength as follows:
for n = 2, h = 3.6456×10−7 m, and m = 3, 4, 5, 6, and so forth. In his 1885 journal he referred to "h" as the "fundamental number of hydrogen." His formula was later revised by Johannes Rydberg as finding the frequency of a wavelength.
Reference: Balmer, Johannes. Wikipedia The Free Encyclopedia. 23 Sept. 2008. Date accessed 3 Dec. 2008. http://en.wikipedia.org/wiki/Johann_Jakob_Balmer
Johannes Robert Rydberg was a Swedish physicist mainly known for devising the Rydberg formula, in 1888, which is used to predict the wavelengths of photons (of light and other electromagnetic radiation) emitted by changes in the energy level of an electron in an atom.
The physical constant known as the Rydberg constant is named after him, as is the Rydberg unit. Excited atoms with very high values of the principal quantum number, represented by n in the Rydberg formula, are called Rydberg atoms, and a crater on the moon is also named Rydberg in his honour. Rydberg's faith that spectral studies could assist in a theoretical understanding of the atom and its chemical properties was justified in 1913 by the work of Niels Bohr (see hydrogen spectrum). An important spectroscopic constant based on a hypothetical atom of infinite mass is called the Rydberg (R) in his honor.
Source of Material - http://en.wikipedia.org/wiki/Johannes_Rydberg
C. Davisson and L. H. Germer; G. P. Thomson
>p Three years after de Broglie asserted that particles of matter could possess wavelike properties, the diffraction of electrons from the surface of a solid crystal was experimentally observed by C. J. Davisson and L. H. Germer of the Bell Telephone Laboratory. In 1927 they reported their investigation of the angular distribution of electrons scattered from nickel. With careful analysis, they showed that the electron beam was scattered by the surface atoms on the nickel at the exact angles predicted for the diffraction of x-rays according to Bragg's formula, with a wavelength given by the de Broglie equation, λ = h / mv. Also in 1927, G. P. Thomson, the son of J. J. Thomson, reported his experiments, in which a beam of energetic electrons was diffracted by a thin foil. Thomson found patterns that resembled the x-ray patterns made with powdered (polycrystalline) samples. This kind of diffraction, by many randomly oriented crystalline grains, produces rings. If the wavelength of the electrons is changed by changing their incident energy, the diameters of the diffraction rings change proportionally, as expected from Bragg's equation.
1.Colwell, Catherine H.. "Famous Experiments: Davisson-Germer." Physics Lab. 2008. 23 Oct 2008 <http://dev.physicslab.org/Document.aspx?doctype=3&filename=AtomicNuclear_DavissonGermer.xml>.
In 1925, Heinsenberg, with mathematical help from Max Born, developed the first version of quantum mechanics, a matrix method of calculating the behavior of electrons and other subatomic particles.The method was superseded as a practical tool soon after by the more intuitive wave equation of Erwin Schrodinger, but the matrix mechanics remains a great intellectual accomplishment.In 1927, the German physicist Werner Heisenberg showed mathematically that it is impossible to measure with complete precision both a particle's velocity and position at the same instant. To measure an electron's position or velocity, we have to bounce another particle off it. Thus, the very act of making the measurement changes the electron's position and velocity. We can not determine both exact position and exact velocity simultaneously, no matter how cleverly we make the measurements. This was Heisenberg's famous uncertainty principle. The theoretical limitations on measuring speed and position are not significant for large objects. For small particles such as the electron, however, these limitations prevent us from ever knowing or predicting where in an atom an electron will be at a particular instant, so we speak of probabilities instead.A few years later he introduced a new quantum number called isotopic spin, which is a quantum-mechanical variable, resembling the angular momentum vector in algebraic structure whose third component distinguished between members of groups of elementary particles. He continued to contribute to particle physics, introducing useful computational techniques in the 1950s.
Consequently, wave mechanics describes the probable locations of electrons in atoms. Wave mechanics views the probability of finding an electron at a given point in space as equal to the square of the amplitude of the electron wave at that point. In each orbital the electron is conveniently viewed as an electron cloud with a varying electron density.
1. James, Brady. Chemistry Matter and Its Changes. 5th Edition. New York: John Wiley & Sons Inc.
2. "Werner Karl Heisenberg." Answers.com. 2008. Answers Corporation. 23 Oct 2008 <http://www.answers.com/topic/werner-heisenberg>.
Fritz Wolfgang London, a theoretical physicist, was born Breslau, Silesia, Germany in 1900. He had a position at the University of Berlin, but lost it due to Hitler's Nazi Party Racial laws in 1933. He emigrated to the United States in 1939, where he then became a professor at Duke University. With his brother Heinz,. he made fundamental contributions to the theories of chemical bonding and intermolecular forces.
London's early work was in the area of intermolecular forces. He observed the attraction between two rare gas atoms at a large distance from each other. This attraction is now known as "London Force".
For atoms and nonpolar molecules, the London dispersion force is the only intermolecular force and is the reason that they exist in solid and liquid states. For polar molecules, the London dispersion force is one part of the van der Waals force as well as the permanent molecular dipole moments.
Source of Material: http://en.wikipedia.org/wiki/Fritz_London
The London Dispersion Forces, named after Fritz London, exist between atoms. They become stronger when dealing with larger atoms, more surface contact between molecules, and larger electron clouds.LDF is a weak intermolecular force that is part of the Van der Waals Force.
LDF exists when electrons try to avoid each other. These forces are exhibited by nonpolar molecules because of the movements of the electrons within the molecules. These forces allow noble gasses to be found in a liquid form because they would otherwise have no attractive forces, and would not conjeal together. Although it may seem odd, these forces are weaker than ionic bonds, and even hydrogen bonds.
Source of Material: http://en.wikipedia.org/wiki/London_dispersion_force
- Hess's law is a law of physical chemistry created by Germain Hess.It is the expansion of the Hess Cycle and used to predict the enthalpy change and conservation of energy regardless of the path through which it is to be determined.
- Hess's law states that because enthalpy is a state function, the enthalpy change of a reaction is the same regardless of what pathway is taken to achieve the products.
- Hess's law has also led to an extension to entropy and free energy. For example the Bordwell thermodynamic cycle takes advantage of easily measured equilibrium and redox potentials to determine experimentally inaccessible Gibbs free energy values.
- The law states that the energy change for any chemical or physical process is independent of the pathway or number of steps required to complete the process. In other words, an energy change is path independent, only the initial and final states being of importance.
Citation: "Hess's law." Wikipedia-the free encyclopedia.3 Dec. 2008. [].
Theodore W Richards
Theodore W. Richards was born in Germantown, Pennsylvania in 1868. When Theodore was only 10 years old, his family moved to Europe for a few years, which greatly influenced his interest in science. Upon returning to the United States, he entered Haverford College at age 14, and eventually graduated from Harvard. He received his PhD in chemistry and began his research by working with oxygen and copper and eventually, developed a new way to determine atomic weights. By 1912, he had determined over 30 atomic weights, with the highest degree of accuracy. At the end of his chemistry career, he and his students had discovered over 55 atomic weights that are still used today. He played a large part in modernizing the concept of an atom. He also did research on atomic and molecular volume. Richards was responsible for introducing the use of transition temperatures and using hydrated salts as fixed points in standard thermometers. However, his biggest achievement was becoming the first American scientist to win the Nobel Prize in Chemistry in 1914. Today, there is an award known as the Theodore William Richards Medal for Conspicuous Achievement in Chemistry and the Theodore William Richards Medal.
- "Theodore W. Richards." Nobel Lectures. The Nobel Foundation. 9 Dec 2008 <http://nobelprize.org/nobel_prizes/chemistry/laureates/1914/richards-bio.html>.
-"Theodore W. Richards." Wikipedia, the free encyclopedia. 16 Sept 2008. 11 Dec 2008 <http://en.wikipedia.org/wiki/Theodore_William_Richards>.
-"The Theodore William Richards Medal." The Northeastern Section of the American Chemical Society. 2008. 11 Dec 2008 <http://www.nesacs.org>.