Ancient (Philosophical) Atomism The earliest known theories were developed in ancient India in the 6th century BCE by Kanada, a Hindu philosopher.Leucippus and Democritus, Greek philosophers in the 5th century BCE, presented their own theory of atoms.Little is known about Leucippus, while the ideas of his student Democritus—who is said to have taken over and systematized his teacher's theory—are known from a large number of reports.
Greek Atomism These ancient atomists theorized that the two fundamental and oppositely characterized constituents of the natural world are indivisible bodies—atoms—and void. The latter is described simply as nothing, or emptiness.Atoms are solid and impenetrable bodies, and intrinsically unchangeable; they can only move about in the void and combine into different clusters. Since the atoms are separated by void, they cannot fuse, but must rather bounce off one another when they collide.All macroscopic objects are in fact combinations of atoms. Everything in the macroscopic world is subject to change, as their constituent atoms shift or move away. Thus, while the atoms themselves persist through all time, everything in the world of our experience is transitory and subject to dissolution.
Plato and Platonists Plato, a Greek philosopher, presented a different kind of physical theory based on indivisibles.In this theory, it is the elemental triangles composing the solids that are regarded as indivisible, not the solids themselves.The term elements (stoicheia) was first used by Plato in about 360 BC, in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a rudimentary treatise on chemistry.
Plato’s 4 elements
Islamic Atomism During the 11th century (in the Islamic Golden Age), Islamic atomists developed atomic theories that represent a synthesis of both Greek and Indian atomism.The most successful form of Islamic atomism was in the Asharite school of philosophy, most notably in the work of the philosopher al-Ghazali (1058-1111). In Asharite atomism, atoms are the only perpetual, material things in existence, and all else in the world is “accidental” meaning something that lasts for only an instant.
Modern atomic theory In the early years of the 19th century, John Dalton developed the first useful atomic theory of matter around 1803 in which he proposed that each chemical element is composed of atoms of a single, unique type, and that though they are both immutable and indestructible, they can combine to form more complex structures (chemical compounds).
John Dalton (1766-1844)
Background of Dalton's Atomic Theory Less than twenty years earlier, in the 1780's, Antoine Lavoisier ushered in a new chemical era by making careful quantitative measurements which allowed the compositions of compounds to be determined with accuracy. He formulated the Law of conservation of mass in 1789, which states that the total mass in a chemical reaction remains constant (that is, the reactants have the same mass as the products). This law suggested to Dalton that matter is fundamentally indestructible.By 1799 enough data had been accumulated for Proust to establish the Law of Constant Composition ( also called the Law of Definite Proportions). This law states that if a compound is broken down into its constituent elements, then the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance. He had synthesized copper carbonate through numerous methods and found that in each case the ingredients combined in the same proportions as they were produced when he broke down natural copper carbonate.
Background of Dalton's Atomic Theory In 1803 Dalton noted that oxygen and carbon combined to make two compounds. Of course, each had its own particular weight ratio of oxygen to carbon (1.33:1 and 2.66:1), but also, for the same amount of carbon, one had exactly twice as much oxygen as the other. This led him to propose the Law of Simple Multiple Proportions, which was later verified by the Swedish chemist Berzelius. In an attempt to explain how and why elements would combine with one another in fixed ratios and sometimes also in multiples of those ratios, Dalton formulated his atomic theory.
Five main points of Dalton's Atomic Theory Chemical Elements are made of tiny particles called atoms All atoms of a given element are identical The atoms of a given element are different from those of any other element Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers of types of atoms. 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.
Additional work of Dalton In 1803 Dalton published his first list of relative atomic weights for a number of substances (though he did not publicly discuss how he obtained these figures until 1808). Dalton estimated the atomic weights according to the mass ratios in which they combined, with hydrogen being the basic unit.
Distinction of Atoms and Molecules In 1811, Avogadro published an article in Journal de physique that clearly drew the distinction between the molecule and the atom. He pointed out that Dalton had confused the concepts of atoms and molecules. That was why Dalton wrongly concluded water as HO, not H2O.Avogadro suggested that: equal volumes of all gases at the same temperature and pressure contain the same number of molecules which is now known as Avogadro's Principle. In other words, the volume of a gas at a given pressure and temperature is proportional to the number of atoms or molecules regardless of the nature of the gas,and the mass of a gas's particles does not affect its volume.
Avogadro's number Avogadro's Principle allowed him to deduce the diatomic nature of numerous gases by studying the volumes at which they reacted.For instance: since two litres of hydrogen will react with just one litre of oxygen to produce two litres of water vapor (at constant pressure and temperature). Thus two molecules of hydrogen can combine with one molecule of oxygen to produce two molecules of water.It meant a single oxygen molecule splits in two in order to form two particles of water. Thus, Avogadro was able to offer more accurate estimates of the atomic mass of oxygen and various other elements, and firmly established the distinction between molecules and atoms.Avogadro's number is the number of "elementary entities" (usually atoms or molecules) in one mole. For example. the number of atoms in exactly 12 grams of carbon-12 is 6.022X10^23.
Brownian motion: molecules in motion In 1827, the British botanist Robert Brown observed that dust particles floating in water constantly jiggled about for no apparent reason. In 1905, Albert Einstein theorized that this Brownian motion was caused by the water molecules continuously knocking the grains about, and developed a hypothetical mathematical model to describe it.This model was validated experimentally in 1911 by French physicist Jean Perrin, thus providing additional validation for particle theory (and by extension atomic theory).
Mendeleev's Periodic table of Elements SCIENTISTS HAD IDENTIFIED over 60 elements by Mendeleev's time (Today over 110 elements are known).In Mendeleev's day (1834-1907). the atom was considered the most basic particle of matter. The building blocks of atoms (electrons, protons, and neutrons) were discovered only later. What Mendeleev and chemists of his time could determine, however, was the atomic weight of each element: how heavy its atoms were in comparison to an atom of hydrogen, the lightest element.
Mendeleev first trained as a teacher in the Pedagogic Institute of St. Petersburg before earning an advanced degree in chemistry in 1856.
Mendeleev’s work AN OVERALL UNDERSTANDING of how the elements are related to each other and why they exhibit their particular chemical and physical properties was slow in coming. Between 1868 and 1870, in the process of writing his book, The Principles of Chemistry, Mendeleev created a table or chart that listed the known elements according to increasing order of atomic weights. When he organized the table into horizontal rows, a pattern became apparent--but only if he left blanks in the table. If he did so, elements with similar chemical properties appeared at regular intervals--periodically--in vertical columns on the table.
Mendeleev’s contribution Mendeleev was bold enough to suggest that new elements not yet discovered would be found to fill the blank places. He even went so far as to predict the properties of the missing elements. Although many scientists greeted Mendeleev's first table with skepticism, its predictive value soon became clear.The discovery of gallium in 1875, of scandium in 1879, and of germanium in 1886 supported the idea underlying Mendeleev's table. Each of the new elements displayed properties that accorded with those Mendeleev had predicted, based on his realization that elements in the same column have similar chemical properties.
Mendeleev said: “I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.” --Mendeleev, Principles of Chemistry, 1905, Vol. II
WHAT MADE Mendeleev’sTABLE PERIODIC? The value of the table gradually became clear, but not its meaning. Scientists soon recognized that the table's arrangement of elements in order of atomic weight was problematic. The atomic weight of the gas argon, which does not react readily with other elements, would place it in the same group as the chemically very active solids lithium and sodium. In 1913 British physicist Henry Moseley confirmed earlier suggestions that an element's chemical properties are only roughly related to its atomic weight (now known to be roughly equal to the number of protons plus neutrons in the nucleus). What really matters is the element's atomic number-the number of electrons its atom carries, which Moseley could measure with X-rays. Ever since, elements have been arranged on the periodic table according to their atomic numbers. The structure of the table reflects the particular arrangement of the electrons in each type of atom. Only with the development of quantum mechanics in the 1920s did scientists work out how the electrons arrange themselves to give the element its properties.
Discovery of subatomic particles Electron - J. J. Thomson 1896Radioactivity - Henri Becquerel 1896Alpha & beta particles - Ernest Rutherford 1899Nucleus - Ernest Rutherford 1907Isotopes - J. J. Thomson 1913Proton - Ernest Rutherford 1918Neutron - James Chadwick 1932
Joseph John Thomson, (1856 –1940)
Contribution of J. J. Thomson He showed that atoms could be further subdivided into negative (which he named electrons) and positive components.He postulated a "Plum Pudding" model for atoms. He calculated the charge to mass ratio (e/m) for the electron by careful observations of the curvature of an electron beam in cathode ray tubes in a magnetic field.
Measurement of Electronic charge Millikan calculated the charge on the electron with his famous oil drop experiment. He measured the static electrical charge on microscopic oil droplets by balancing droplets between charged plates. He was awarded the Nobel Prize in Physics (1923)
Discovery of the nucleus They discovered that the particles bounced off of something dense in the foil. From this experiment Rutherford postulated that atoms are formed of a small dense positively charged nucleus "orbited" by negatively charged electrons. This led him to his theory that most of the atom was made up of 'empty space'. Ernest Rutherford (1871-1937) was Nobel Prize winner in 1908.
Rutherford's scattering experiment
Rutherford’s gold foil experiment Top: Expected results: alpha particles passing through the plum pudding model of the atom with negligible deflection. Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.
Discovery of isotopes In 1913, J. J. Thomson channeled a stream of neon ions through magnetic and electric fields, striking a photographic plate on the other side. He observed two glowing patches on the plate, which suggested two different deflection trajectories.Thomson concluded this was because some of the neon ions had a different mass; thus did he discover the existence of isotopes.
Radioactivity In 1896, Henri Becquerel discovered that a sample of uranium was able to expose a photographic plate even when the sample and plate were separated by black paper. He also discovered that the exposure of the plate did not depend on the chemical state of the uranium (what uranium compound was used) and therefore must be due to some property of the uranium atom itself.
Properties of stable nuclides The stable nuclides lie in a very narrow band of neutron-to-proton ratios. The ratio of neutrons to protons in stable nuclides gradually increases as the number of protons in the nucleus increases. Light nuclides, such as 12C, contain about the same number of neutrons and protons. Heavy nuclides, such as 238U, contain up to 1.6 times as many neutrons as protons. There are no stable nuclides with atomic numbers larger than 83. This narrow band of stable nuclei is surrounded by a sea of instability. Nuclei that lie above this line have too many neutrons and are therefore neutron-rich. Nuclei that lie below this line don't have enough neutrons and are therefore neutron-poor.
Three Types of Radioactive Decay: Alpha Decay
Beta Decay is the process in which an electron is ejected or emitted from the nucleus
Gamma Decay
Radiation therapy Even radioactivity can induce cancer in a living organism, controlled application of nuclear radiations are successfully employed in the treatment of certain cancers.Radiation therapy is the use of a certain type of (ionizing) radiation to kill cancer cells and shrink tumors that cannot be safely or completely removed by surgery. It is also used to treat cancers that are not affected by chemotherapy. Radiation therapy injures or destroys cells in the area being treated (the “target tissue”) by damaging their genetic material, making it impossible for these cells to continue to grow and divide. Radiation damages both cancer cells and normal cells. However, most normal cells can recover from the effects of radiation and function properly. The goal of radiation therapy is to damage as many cancer cells as possible, while limiting harm to nearby healthy tissue.
Dating By Radioactive Decay Just after World War II, Willard F. Libby proposed a way to use Radioactive Decay of C14 to estimate the age of carbon-containing substances. The C14 dating technique for which Libby received the Nobel prize was based on the following assumptions. - C14 is produced in the atmosphere at a more or less constant rate.
- Carbon atoms circulate between the atmosphere, the oceans, and living organisms at a rate very much faster than they decay. As a result, there is a constant concentration of 14C in all living things.
- After death, organisms no longer pick up 14C.
By comparing the activity of a sample with the activity of living tissue we can estimate how long it has been since the organism died.
Introduction to quantum mechanics 1900 - Max Planck's landmark paper on black body radiation.1905 - Albert Einstein extended Planck's theory to explain the photoelectric effect.1913 - Niels Bohr introduced his model of the atom, incorporating Planck's quantum hypothesis.1924 - Louis de Broglie proposed the matter-wave hypothesis1925, Heisenberg introduced matrix mechanics & Heisenberg's Uncertainty Principle1926 - Erwin Schrödinger analyzed how an electron would behave if it were assumed to be a wave surrounding a nucleus (Schrödinger's equation).
Light : Wave–particle duality In the 1600s, competing theories of light were proposed by Christiaan Huygens and Isaac Newton: light was thought either to consist of waves (Huygens) or of particle (Newton).Light was believed to be a wave, after Thomas Young's double-slit interference experiment and effects such as diffraction had clearly demonstrated the wave-like nature of light.
So light is a form of wave! In the late 1800s, James Clerk Maxwell explained light as the propagation of electromagnetic waves according to the Maxwell equations. These equations were verified by experiment by Heinrich Hertz in 1887, and the wave theory became widely accepted.During the late nineteenth century, no one ever doubled that light is a form of wave.
The Ultraviolet catastrophe However, in late 19th century/early 20th century classical physics led to the prediction that an ideal black body at thermal equilibrium will emit radiation with infinite power. This error is embodied in the Rayleigh–Jeans law for the energy emitted by an ideal black-body at short wavelengths. In 1901, Max Planck published an analysis that succeeded in reproducing the observed spectrum of light emitted by a glowing object. To accomplish this, Planck had to make a mathematical assumption of quantized energy of the oscillators (atoms of the black body) that emit radiation. It was Einstein who later proposed that it is the electromagnetic radiation itself that is quantized, and not the energy of radiating atoms.
Planck's constant Classical physics predicted that a black-body radiator would emit an infinite amount of energy. Not only was this prediction absurd, but the observed emission spectrum of a black-body rose from zero at one end, peaked at a frequency related to the temperature of the radiator, and then declined to zero.In 1900, Max Planck developed an empirical equation that could account for the observed emission spectra of black bodies assuming that the energy E of any one oscillator was proportional to some integral multiple of its frequency f,
Photons & Photoelectric effect
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. Only a limited number of orbits with certain energies are allowed. In other words, the orbits are quantized. The only orbits that are allowed are those for which the angular momentum of the electron is an integral multiple of Planck's constant divided by 2pi. Light 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 light emitted or absorbed is exactly equal to the difference between the energies of the orbits.
De Broglie (matter) wave In 1924, Louis-Victor de Broglie formulated the de Broglie hypothesis, claiming that all matter, not just light, has a wave-like nature; he related wavelength (denoted as λ), and momentum (denoted as p):
Wave-particle duality Light – Wave? Particle?Electron, proton … - Wave? Particle?
Full quantum mechanical theory De Broglie’s matter-wave hypothesis (1924) quickly led to a more sophisticated and complete variant of atomic theory called the "new quantum mechanics" with important contributors like: Max Born, Paul Dirac, Werner Heisenberg, Wolfgang Pauli, and Erwin Schrödinger.In 1925, Werner Heisenberg (won the Nobel Prize in Physics in 1932) developed the matrix mechanics formulation of quantum mechanics.In 1926 Erwin Schrödinger published the Schrödinger equation and showed that it gave the correct energy eigenvalues for the hydrogen-like atom. He won the Nobel Prize in Physics in 1933.
Matrix mechanics & Schrödinger's equation Matrix mechanics was the first complete and correct definition of quantum mechanics. It extended the Bohr Model by describing how the quantum jumps occur. It did so by interpreting the physical properties of particles as matrices that evolve in time. Schrödinger equation is an equation that describes how the quantum state of a physical system changes in time. It is as central to quantum mechanics as Newton's laws are to classical mechanics.In the standard interpretation of quantum mechanics, the quantum state, also called a wavefunction or state vector, is the most complete description that can be given to a physical system. Solutions to Schrödinger's equation describe not only atomic and subatomic systems, electrons and atoms, but also macroscopic systems.Schrödinger's equation can be mathematically transformed into Heisenberg's matrix mechanics.
Wave functions
Eigen-state & eigen-energy of the Schrödinger equation Time-independent Schrödinger equation in quantum mechanics:
Quantum chemistry Properties of all chemical compound can be obtained from solution of the time-independent Schrödinger equation.For example: ChemViz (Chemistry Visualization) is an interactive chemistry program which incorporates computational chemistry simulations and visualizations for use in the chemistry classroom. The chemistry simulations support the chemistry principles teachers are trying to convey, and the visualizations allow students to see how matter interacts at an atomic level. (http://education.ncsa.illinois.edu/products/chemviz/index.html)
Superposition principle of wave
In probability theory with a finite number of states, the probabilities can always be multiplied by a positive number to make their sum equal to one. For example, if there is a three state probability system:
Quantum Superposition
Copenhagen interpretation of quantum mechanics In quantum mechanics, the state of every particle (e.g. electron) is described by a wavefunction, which is just a mathematical tool used to calculate the probability for it to be found in a state (of motion) that can be measured by experiment.Before the measurement, the wavefunction is a superposition of all possible states that is consistent with the constraint of the system.The act of measurement causes the wavefunction to "collapse" to the state defined by the result of the measurement. Interpretation first suggested by Bohr and Heisenberg in the course of their collaboration in Copenhagen around 1927.
Dissatisfaction with Copenhagen interpretation God doesn't play dice -- Albert EinsteinSchrödinger's Cat -- Shows that our consciousness and knowledge are somehow mixed up in the process of observation.
Schrödinger's Cat
Heisenberg’s Uncertainty principle In quantum mechanics, a particle is described by a wave. The position is where the wave is concentrated and the momentum is the wavelength. The position is uncertain to the degree that the wave is spread out, and the momentum is uncertain to the degree that the wavelength is ill-defined.
Quantum tunneling
Influence of QM - Philosophy of physics or metaphysics Interpretations of quantum mechanics are attempts to explain how quantum mechanics change our understanding of nature. Even quantum mechanics has received thorough experimental testing, many of these experiments are open to different interpretations. There exist a number of contending schools of thought, differing over whether quantum mechanics can be understood to be deterministic, which elements of quantum mechanics can be considered "real", and other related matters.Observation/measurement will interact with and change the physical world. In other words, reality is being affected by the observer. Is there an objective physical world existed independent of the observer?
Influence of QM - finance Inspired by Heisenberg's rule about quantum particles, George Soros proclaims a human uncertainty principle which suggests our understanding is often incoherent and always incomplete. From his case study, one notices that uncertainty continually besets Mr. Soros in managing his hedge fund, which has the same name as the particles subject to Heisenberg's uncertainty principle. He named the fund he created the Quantum Fund.Quantum Finance - Quantum theory is used to model secondary financial markets.
Influence of QM – quantum computer A quantum computer is a device for computation that makes direct use of quantum mechanical phenomena, such as superposition, to perform operations on data. The basic principle behind quantum computation is that quantum properties can be used to represent data and perform operations on these data.
Glossary A.D. - "Abbreviation for the term Anno Domini Nostri Jesu Christi (or simply Anno Domini) which means ""in the year of our Lord Jesus Christ."" Years are counted from the traditionally recognized year of the birth of Jesus. In academic, historical, and archaeological circles, A.D. is generally replaced by the term Common Era (C.E.).“B.C. - Abbreviation for the term Before Christ. Years are counted back from the traditionally recognized year of Christ's birth. In academic, historical, and archaeological circles, this term is now generally replaced by Before Common Era (B.C.E.). B.C.E. - Before Common Era. See B.C.
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