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For atomic theories in model theory, see atomic model. In Mathematics, model theory is the study of (classes of mathematical structures such as groups, Fields graphs or even models In Model theory, an atomic model is a model which is in some sense small

This article focuses on the historical models of the atom. For a history of the study of how atoms combine to form molecules, see History of the molecule. In Chemistry, the history of the Molecule traces the origins of the concept or idea of the existence of strong chemical bonds between two or more Atoms

In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. The word theory has many distinct meanings in different fields of Knowledge, depending on their methodologies and the context of discussion. Matter is commonly defined as being anything that has mass and that takes up space. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny It began as a philosophical concept in ancient Greece and India and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up particles.

The name "atom" (from the Greek word atomos, which means "indivisible"[1]) was attributed to the basic particle that constituted a chemical element, because the chemists of the era believed that these were the fundamental particles of matter. However, around the turn of the 20th century, through various experiments with electromagnetism and radioactivity, physicists discovered that the so-called "indivisible atom" was actually a conglomerate of various subatomic particles (chiefly, electrons, protons and neutrons) which can exist separately from each other. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. In fact, in certain extreme environments such as neutron stars, extreme temperature and pressure prevents atoms from existing at all. A neutron star is a type of remnant that can result from the Gravitational collapse of a massive Star during a Type II, Type Ib or Type The field of science which studies subatomic particles is particle physics, and it is in this field that physicists hope to discover the true fundamental nature of matter. Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them

Contents

Philosophical atomism

Main article: Atomism

The concept that matter is composed of discrete units and cannot be divided into any arbitrarily small quantities has been around for thousands of years, but these ideas were founded in abstract, philosophical reasoning rather than scientific experimentation. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in The nature of atoms in philosophy varied considerably over time and between cultures and schools, and often had spiritual elements. Nevertheless, the basic idea of the atom was adopted by scientists thousands of years later because it could elegantly explain new discoveries in the field of chemistry.

Indian

Some of the earliest known theories were developed in ancient India in the 6th century BCE by Kanada, a Hindu philosopher. Kanada ( Sanskrit: कणाद; also transliterated as Canada as well as other forms was a Hindu sage who founded the philosophical A Hindu ( Devanagari: हिन्दू is an adherent of the philosophies and scriptures of Hinduism, a set of religious, Philosophical [2] In Hindu philosophy, the Nyaya and Vaisheshika schools developed elaborate theories on how atoms combined into more complex objects (first in pairs, then trios of pairs),[2] but believed the interactions were ultimately driven by the will of God (specifically, the Hindu Ishvara), and that the atoms themselves were otherwise inactive, without physical properties of their own. Nyāya ( Sanskrit ni-āyá, literally "recursion" used in the sense of " Syllogism, inference" is the name given to one of the six orthodox Vaisheshika, or Vaiśeṣika, (Sanskrit वैशॆषिक) is one of the six Hindu schools of Philosophy (orthodox Vedic systems Ishvara ( Sanskrit: Īśvara sa ईश्वर Malay: Iswara, Thai: Phra Isuan) is a philosophical concept in Hinduism By contrast, Jainic philosophy linked the behavior of matter to the nature of the atoms themselves. Each atom, according to Jaina philosophy, has one kind of taste, one smell, one color, and two kinds of touch, though it is unclear what was meant by “kind of touch”. Atoms can exist in one of two states: subtle, in which case they can fit in infinitesimally small spaces, and gross, in which case they have extension and occupy a finite space. Although atoms are made of the same basic substance, they can combine based on their eternal properties to produce any of six “aggregates,” which seem to correspond with the Greek concept of “elements”: earth, water, shadow, sense objects, karmic matter, and unfit matter. [3]

Greek

In the 5th century BCE, Democritus developed the concept of atoms in order to reconcile two conflicting schools of thought on the nature of reality. Democritus ( Greek:) was a pre-Socratic Greek Materialist Philosopher (born at Abdera in Thrace ca On one side was Heraclitus, who believed that the nature of all existence is change. Heraclitus of Ephesus ( Ancient Greek: &mdash grc-Latn ''Hērákleitos ho Ephésios'' English Heraclitus the Ephesian) (ca On the other side was Parmenides, who believed instead that all change is illusion. Parmenides of Elea ( Greek:, early 5th century BC was an Ancient Greek Philosopher born in Elea, a Greek city on the southern coast of

Parmenides denied the existence of motion, change and void. He believed all existence to be a single, all-encompassing and unchanging mass (a concept known as monism), and that change and motion were mere illusions. Monism is the metaphysical and Theological view that all is one that all reality is subsumed under the most fundamental category of being or existence This conclusion, as well as the reasoning that lead to it, may indeed seem baffling to the modern empirical mind, but Parmenides explicitly rejected sensory experience as the path to an understanding of the universe, and instead used purely abstract reasoning. Firstly, he believed there is no such thing as void, equating it with non-being (ie "if the void is, then it is not nothing; therefore it is not the void"). This in turn meant that motion is impossible, because there is no void to move into. [4] He also wrote all that is must be an indivisible unity, for if it were manifold, then there would have to be a void that could divide it (and he did not believe the void exists). Finally, he stated that the all encompassing Unity is unchanging, for the Unity already encompasses all that is and can be.

Democritus accepted most of Parmenides's arguments, except for the idea that change is an illusion. He believed change was real, and if it was not then at least the illusion had to be explained. He thus supported the concept of void, and stated that the universe is made up of multiple indivisble Parmenidean entities that move around in the void. These entities, which are, are indeed unchangeable and indivisible ("atomos", the Greek word for uncuttable), but their arrangement in space is constantly changing. Democritus's atoms were made of the same material but had a limitless variety of shapes and sizes; this, coupled with their arrangement in space, explained all the different substances and objects in the universe. [5]

Islamic

During the 11th century (in the Islamic Golden Age), Islamic atomists developed atomic theories that represent a synthesis of both Greek and Indian atomism. In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in In Natural philosophy, atomism is the theory that all the objects in the universe are composed of very small indestructible building blocks - Atoms Or stated in Older Greek and Indian ideas were further developed by Islamic atomists, along with new Islamic ideas, such as the possibility of there being particles smaller than an atom. 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. Nothing accidental can be the cause of anything else, except perception, as it exists for a moment. Contingent events are not subject to natural physical causes, but are the direct result of God’s constant intervention, without which nothing could happen. Thus nature is completely dependent on God, which meshes with other Asharite Islamic ideas on causation, or the lack thereof. [6]

Modern atomic theory

Birth

In the early years of the 19th century, John Dalton developed his atomic theory 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 FRS (6 September 1766 &ndash 27 July 1844 was an English Chemist, Meteorologist and Physicist. How precisely Dalton arrived at his theory is not entirely clear, but nonetheless it allowed him to explain various new discoveries in chemistry that he and his contemporaries made.

The first was the law of conservation of mass, formulated by Antoine Lavoisier 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). The law of conservation of mass/matter, also known as law of mass/matter conservation (or the Lomonosov - Lavoisier law says that the Mass of [7] This law suggested to Dalton that matter is fundamentally indestructible.

The second was the law of definite proportions. In Chemistry, the law of definite proportions and also the elements states that a Chemical compound always contains exactly the same proportion of elements First proven by the French chemist Joseph Louis Proust in 1799,[8] 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. Joseph Louis Proust ( September 26, 1754 - July 5, 1826) was a French Chemist. Proust 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.

Dalton studied and expanded upon Proust's work to develop the law of multiple proportions: if two elements form more than one compound between them, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small integers. In Chemistry, the law of multiple proportions is one of the basic laws and a major tool of chemical measurement ( Stoichiometry) The integers (from the Latin integer, literally "untouched" hence "whole" the word entire comes from the same origin but via French One pair of reactions Dalton studied involved the combinations of "nitrous air", or what we now call nitric oxide (NO), and oxygen (O2). Nitric oxide or nitrogen monoxide is a Chemical compound with Chemical formula N[[Oxygen O]] Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Under certain conditions, these gases formed an unknown product at a certain combining ratio (now known to be nitrogen dioxide (NO2)), but when he repeated the reaction under other conditions, exactly twice the amount of nitric oxide (a ratio of 1:2 -- small integers) reacted completely with oxygen to form a different product -- now known as dinitrogen trioxide (N2O3). Nitrogen dioxide is the Chemical compound with the formula N[[Oxygen O]]2 Dinitrogen trioxide is the Chemical compound with the formula N2O3

2NO + O2 → 2NO2

4NO + O2 → 2N2O3

Dalton also believed atomic theory could explain why water absorbed different gases in different proportions: for example, he found that water absorbed carbon dioxide far better than it absorbed nitrogen. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Dalton hypothesized this was due to the differences in mass and complexity of the gases' respective particles. Indeed, carbon dioxide molecules (CO2) are heavier and larger than nitrogen molecules (N2).

Various atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy (1808).
Various atoms and molecules as depicted in John Dalton's A New System of Chemical Philosophy (1808). John Dalton FRS (6 September 1766 &ndash 27 July 1844 was an English Chemist, Meteorologist and Physicist.

In 1803 Dalton orally presented his first list of relative atomic weights for a number of substances. This paper was published in 1805, but he did not discuss there exactly how he obtained these figures. [9] The method was first revealed in 1807 by his acquaintance Thomas Thomson, in the third edition of Thomson's textbook, A System of Chemistry. Thomas Thomson FRS ( 12 April, 1773 &ndash 2 July, 1852) was a Scottish Chemist whose writings contributed Finally, Dalton published a full account in his own textbook, A New System of Chemical Philosophy, 1808 and 1810.

Dalton estimated the atomic weights according to the mass ratios in which they combined, with hydrogen being the basic unit. However, Dalton did not conceive that with some elements atoms exist in molecules – e. g. pure oxygen exists as O2. He also mistakenly believed that the simplest compound between any two elements is always one atom of each (so he thought water was HO, not H2O). [10] This, in addition to the crudity of his equipment, resulted in his table being highly flawed. For instance, he believed oxygen atoms were 5. 5 times heavier than hydrogen atoms, because in water he measured 5. 5 grams of oxygen for every 1 gram of hydrogen and believed the formula for water was HO (an oxygen atom is actually 16 times heavier than a hydrogen atom).

The flaw in Dalton's theory was corrected in 1811 by Amedeo Avogadro. Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto, Count of Quaregna and Cerreto was an Italian Savant. Avogadro had proposed that equal volumes of any two gases, at equal temperature and pressure, contain equal numbers of molecules (in other words, the mass of a gas's particles does not affect its volume). [11] Avogadro's law allowed him to deduce the diatomic nature of numerous gases by studying the volumes at which they reacted. Avogadro's law ( Avogadro's Hypothesis, or Avogadro's Principle) is a Gas law named after Amedeo Avogadro, who in 1811 hypothesized For instance: since two liters of hydrogen will react with just one liter of oxygen to produce two liters of water vapor (at constant pressure and temperature), 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.

In 1827, the British botanist Robert Brown observed that pollen particles floating in water constantly jiggled about for no apparent reason. Robert Brown FRS ( 21 December, 1773 &ndash 10 June, 1858) was a Scottish scientist who is acknowledged as the leading botanist 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. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical This article is about the physical phenomenon for the stochastic process see Wiener process. [12] This model was validated experimentally in 1908 by French physicist Jean Perrin, thus providing additional validation for particle theory (and by extension atomic theory). Jean Baptiste Perrin ( September 30, 1870 &ndash April 17, 1942) was a French Physicist and Nobel laureate.

Discovery of subatomic particles

Thomson's Crookes tube in which he observed the deflection of cathode rays by an electric field. The purple line represents the deflected electron stream.
Thomson's Crookes tube in which he observed the deflection of cathode rays by an electric field. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays The purple line represents the deflected electron stream.

Atoms were thought to be the smallest possible division of matter until 1897 when J.J. Thomson discovered the electron through his work on cathode rays. Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Cathode rays (also called an electron beam or e-beam) are streams of Electrons observed in Vacuum tubes i [13] A Crookes tube is a sealed glass container in which two electrodes are separated by a vacuum. A Crookes tube is an early experimental Discharge tube, invented by British physicist William Crookes and others around 1875 in which Cathode rays When a voltage is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube. Cathode rays (also called an electron beam or e-beam) are streams of Electrons observed in Vacuum tubes i Through experimentation, Thomson discovered that the rays could be deflected by an electric field (in addition to magnetic fields, which was already known). He concluded that these rays, rather than being waves, were composed of negatively charged particles he called "corpuscles" (they would later be renamed electrons by other scientists).

Thomson believed that the corpuscles emerged from the very atoms of the electrode. He thus concluded that atoms were divisible, and that the corpuscles were their building blocks. To explain the overall neutral charge of the atom, he proposed that the corpuscles were distributed in a uniform sea or cloud of positive charge; this was the plum pudding model. The plum pudding model of the Atom by JJ Thomson, who discovered the Electron in 1897 was proposed in 1904 before the discovery of the atomic nucleus [14]

Since atoms were found to be actually divisible, physicists later invented the term "elementary particles" to describe indivisible particles. In Particle physics, an elementary particle or fundamental particle is a particle not known to have substructure that is it is not known to be made

Discovery of the nucleus

The 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.
The 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.

Thomson's plum pudding model was disproved in 1909 by one of his students, Ernest Rutherford, who discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very center. The plum pudding model of the Atom by JJ Thomson, who discovered the Electron in 1897 was proposed in 1904 before the discovery of the atomic nucleus Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist

In the gold foil experiment, Hans Geiger and Ernest Marsden (colleagues of Rutherford working at his behest) shot alpha particles through a thin sheet of gold, striking a fluorescent screen that surrounded the sheet. The Geiger-Marsden experiment (also called the Gold foil experiment or the Rutherford experiment) was an experiment done by Hans Geiger and Ernest Johannes (Hans Wilhelm Geiger ( September 30, 1882 &ndash September 24, 1945) was a German Physicist. Sir Ernest Marsden ( 19 February 1889 - 15 December 1970) was a English - New Zealand Physicist. Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Fluorescence is a Luminescence that is mostly found as an [15] Given the very small mass of the electrons, the high momentum of the alpha particles and the unconcentrated distribution of positive charge of the plum pudding model, the experimenters expected all the alpha particles to either pass through without significant deflection or be absorbed. To their astonishment, a small fraction of the alpha particles experienced heavy deflection. This led Rutherford to propose the planetary model of the atom in which pointlike electrons orbited in the space around a massive, compact nucleus—like planets orbiting the Sun. The nucleus of an Atom is the very dense region consisting of Nucleons ( Protons and Neutrons, at the center of an atom [16]

Discovery of isotopes

While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one element at each position on the atomic table. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Radiochemistry is the Chemistry of Radioactive materials where radioactive Isotopes of elements are used to study the properties and Chemical reactions Frederick Soddy ( 2 September 1877 &ndash 22 September 1956) was an English radiochemist. [17] The term isotope was coined by Margaret Todd as a suitable name for these elements. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides Margaret Todd (1859 &ndash 1918 was a Scottish writer and doctor who in 1913 suggested the term Isotope to chemist Frederick Soddy.

That same year, J.J. Thomson conducted an experiment in which he channeled a stream of neon ions through magnetic and electric fields, striking a photographic plate at the other end. Sir Joseph John “JJ” Thomson, OM, FRS (18 December 1856 &ndash 30 August 1940 was a British Physicist and Nobel laureate 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. [18] The nature of this differing mass would later be explained by the discovery of neutrons in 1932.

Discovery of nuclear particles

See also: Prout's hypothesis

In 1918, Rutherford bombarded nitrogen gas with alpha particles and observed hydrogen nuclei being emitted from the gas. Prout's hypothesis was an early 19th century attempt to explain the existence of the various Chemical elements through a hypothesis regarding the internal structure of the Ernest Rutherford 1st Baron Rutherford of Nelson, OM, PC, FRS (30 August 1871 – 19 October 1937 was a New Zealand Physicist Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Rutherford concluded that the hydrogen nuclei emerged from the nuclei of the nitrogen atoms themselves (in effect, he split the atom). [19] He later found that the positive charge of any atom could always be equated to that of an integer number of hydrogen nuclei. This, coupled with the facts that hydrogen was the lightest element known and that the atomic mass of every other element was roughly equivalent to a whole multiple of hydrogen's atomic mass, led him to conclude hydrogen nuclei were singular particles and a basic constituent of all atomic nuclei: the proton. The atomic mass (ma is the Mass of an atom most often expressed in unified atomic mass units The atomic mass may be considered to be the total mass The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive Further experimentation by Rutherford found that the nuclear mass of most atoms exceeded that of the protons it possessed; he speculated that this surplus mass was composed of hitherto unknown neutrally charged particles, which were tentatively dubbed "neutrons".

In 1928, Walter Bothe observed that beryllium emitted a highly penetrating, electrically neutral radiation when bombarded with alpha particles. Walther Wilhelm Georg Bothe (8 January 1891 in Oranienburg &ndash 8 February 1957 in Heidelberg) was a German nuclear physicst Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 It was later discovered that this radiation could knock hydrogen atoms out of paraffin wax. Initially it was thought to be high-energy gamma radiation, since gamma radiation had a similar effect on electrons in metals, but James Chadwick found that the ionisation effect was too strong for it to be due to electromagnetic radiation. Sir James Chadwick, CH (20 October 1891 &ndash 24 July 1974 was an English Physicist and Nobel laureate in physics awarded for his discovery of the In 1932, he exposed various elements, such as hydrogen and nitrogen, to the mysterious "beryllium radiation", and by measuring the energies of the recoiling charged particles, he deduced that the radiation was actually composed of electrically neutral particles with a mass similar to that of a proton. [20] For his discovery of the neutron, Chadwick received the Nobel Prize in 1935. This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron.

Quantum physical models of the atom

The planetary model of the atom had shortcomings. Firstly, according to the Larmor formula in classical electromagnetism, an accelerating electric charge emits electromagnetic waves; an orbiting charge would steadily lose energy and spiral towards the nucleus, colliding with it in a small fraction of a second. In Physics, in the area of Electrodynamics, the Larmor formula is used to calculate the total power radiated by a nonrelativistic point charge as it accelerates Classical electromagnetism (or classical electrodynamics) is a theory of Electromagnetism that was developed over the course of the 19th century most prominently Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. Another phenomenon the model did not explain was why excited atoms only emit light within certain discrete spectra. An element's 'emission spectrum' is the relative intensity of Electromagnetic radiation of each Frequency it emits when it is Heated (or more generally when

The Bohr model of the atom
The Bohr model of the atom

Quantum theory revolutionized physics at the beginning of the 20th century, when Max Planck and Albert Einstein postulated that light energy is emitted or absorbed in discrete amounts known as quanta (singular, quantum). In Atomic physics, the Bohr model created by Niels Bohr depicts the Atom as a small positively charged nucleus surrounded by Electrons Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical In 1913, Niels Bohr incorporated this idea into his Bohr model of the atom, in which the electrons could only orbit the nucleus in particular circular orbits with fixed angular momentum and energy, their distances from the nucleus being proportional to their respective energies. Niels Henrik David Bohr (nels ˈb̥oɐ̯ˀ in Danish 7 October 1885 – 18 November 1962 was a Danish Physicist who made fundamental contributions to understanding In Atomic physics, the Bohr model created by Niels Bohr depicts the Atom as a small positively charged nucleus surrounded by Electrons In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position [21] Under this model electrons could not spiral into the nucleus because they could not lose energy in a continuous manner; instead, they could only make instantaneous "quantum leaps" between the fixed energy levels. In Physics, a quantum leap or quantum jump is a change of an Electron from one energy state to another within an Atom. A quantum mechanical system or particle that is bound, confined spacially can only take on certain discrete values of energy as opposed to classical particles which [21] When this occurred, light was emitted or absorbed at a frequency proportional to the change in energy (hence the absorption and emission of light in discrete spectra). [21]

Bohr's model was only able to predict the spectral lines of hydrogen; it couldn't predict those of multielectron atoms. Worse still, as spectrographic technology improved, additional spectral lines in hydrogen were observed which Bohr's model couldn't explain. In 1916, Arnold Sommerfeld added elliptical orbits to the Bohr model to explain the extra emission lines, but this made the model very difficult to use, and it still couldn't explain complex atoms. Arnold Johannes Wilhelm Sommerfeld (5 December 1868 &ndash 26 April 1951 was a German theoretical Physicist who pioneered developments in atomic

In 1924, Louis de Broglie proposed that all moving particles–particularly subatomic particles such as electrons–exhibit a degree of wave-like behavior. Louis-Victor-Pierre-Raymond 7th duc de Broglie, FRS (də bʁœj ( August 15 1892 &ndash March 19 1987) was a French Erwin Schrödinger, fascinated by this idea, explored whether or not the movement of an electron in an atom could be better explained as a wave rather than as a particle. Schrödinger's equation, published in 1926,[22] describes an electron as a wavefunction instead of as a point particle, and it elegantly predicted many of the spectral phenomena Bohr's model failed to explain. In Physics, especially Quantum mechanics, the Schrödinger equation is an equation that describes how the Quantum state of a Physical system Although this concept was mathematically convenient, it was difficult to visualize, and faced opposition. [23] One of its critics, Max Born, proposed instead that Schrödinger's wavefunction described not the electron but rather all its possible states, and thus could be used to calculate the probability of finding an electron at any given location around the nucleus. Max Born (11 December 1882 &ndash 5 January 1970 was a German Physicist and Mathematician who was instrumental in the development of Quantum [24]

The five atomic orbitals of a neon atom, separated and arranged in order of increasing energy from left to right, with the last three orbitals being equal in energy. Each orbital holds up to two electrons, which exist for most of the time in the zones represented by the colored bubbles. Each electron is equally in both orbital zones, shown here by color only to highlight the different wave phase.
The five atomic orbitals of a neon atom, separated and arranged in order of increasing energy from left to right, with the last three orbitals being equal in energy. This article refers to physical states having the same energy Each orbital holds up to two electrons, which exist for most of the time in the zones represented by the colored bubbles. Each electron is equally in both orbital zones, shown here by color only to highlight the different wave phase.

Since a wavefunction incorporates time as well as position, it is impossible to simultaneously derive precise values for both the position and momentum of a particle for any given point in time; this became known as the uncertainty principle. In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain This invalidated Bohr's model, with its neat, clearly defined circular orbits. The modern model of the atom describes the positions of electrons in an atom in terms of probabilities. An electron can potentially be found at any distance from the nucleus, but—depending on its energy level—tends to exist more frequently in certain regions around the nucleus than others; this pattern is referred to as its atomic orbital. An atomic orbital is a Mathematical function that describes the wave-like behavior of an electron in an atom

See also

Notes

  1. ^ Atom. In Chemistry, the history of the Molecule traces the origins of the concept or idea of the existence of strong chemical bonds between two or more Atoms Quantum mechanics (QM or quantum theory) is a physical science dealing with the behavior of Matter and Energy on the scale of Atoms Kinetic theory (or kinetic theory of gases) attempts to explain Macroscopic properties of Gases such as pressure temperature or volume by considering Merriam-Webster Online Dictionary. Retrieved on 2008-02-10. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1355 - The St Scholastica's Day riot breaks out in Oxford, England, leaving 63 scholars and perhaps 30 locals dead
  2. ^ a b Teresi, Dick (2003). Lost Discoveries: The Ancient Roots of Modern Science. Simon & Schuster, 213–214. ISBN 074324379X.  
  3. ^ Gangopadhyaya, Mrinalkanti. Indian Atomism: History and Sources. Atlantic Highlands, New Jersey: Humanities Press, 1981. ISBN 0-391-02177-X
  4. ^ Bertrand Russel. (1946). History of Western Philosophy. pg 75. ISB 0-415-32505-6
  5. ^ Andre G. van Melsen. (1952) From Atomos to Atom. ISBN 0-486-49584-1
  6. ^ Gardet, L. “djuz’” in Encyclopaedia of Islam CD-ROM Edition, v. 1. 1. Leiden: Brill, 2001.
  7. ^ Weisstein, Eric W. "Lavoisier, Antoine (1743-1794). " scienceworld. wolfram. com. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  8. ^ Proust, Joseph Louis. "Researches on Copper", excerpted from Ann. chim. 32, 26-54 (1799) [as translated and reproduced in Henry M. Leicester and Herbert S. Klickstein, A Source Book in Chemistry, 1400-1900 (Cambridge, MA: Harvard, 1952)]. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  9. ^ Dalton, John. "On the Absorption of Gases by Water and Other Liquids", in Memoirs of the Literary and Philosophical Society of Manchester. 1803. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  10. ^ Johnson, Chris. "Avogadro - his contribution to chemistry. " Last modified on July 4, 2004. Events 836 - Pactum Sicardi, peace between the Principality of Benevento and the Duchy of Naples "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  11. ^ Avogadro, Amedeo. "Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds. " 1811. Journal de Physique, 73, 58-76. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  12. ^ Einstein, Albert. "On the Movement of Small Particles Suspended in Stationary Liquids Required by the Molecular-Kinetic Theory of Heat. " Annal der Physik. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  13. ^ Thomson, J. J. "Cathode rays. " Philosophical Magazine, 44, 293 (1897). [facsimile from Stephen Wright, Classical Scientific Papers, Physics (Mills and Boon, 1964). ] Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  14. ^ Thomson, J. J. "On the Structure of the Atom: an Investigation of the Stability and Periods of Oscillation of a number of Corpuscles arranged at equal intervals around the Circumference of a Circle; with Application of the Results to the Theory of Atomic Structure. " Philosophical Magazine March 1904. Series 6, Vol 7, No 39. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  15. ^ Geiger, H. "The Scattering of the α-Particles by Matter. " Proceedings of the Royal Society February 17, 1910. Events 1500 - Battle of Hemmingstedt. 1600 - Philosopher Giordano Bruno is burned alive at Campo de' Fiori Year 1910 ( MCMX) was a Common year starting on Saturday (link will display calendar of the Gregorian calendar (or a Common year starting Series A 82: 495–500. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  16. ^ Rutherford, Ernest. "The Scattering of α and β Particles by Matter and the Structure of the Atom. " Philosophical Magazine. May 1911. Series 6, Vol. 21. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  17. ^ Frederick Soddy, The Nobel Prize in Chemistry 1921. Nobel Foundation. Retrieved on 2008-01-18. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 350 - Generallus Magnentius deposes Roman Emperor Constans and proclaims himself Emperor
  18. ^ Thomson, J. J. "Rays of positive electricity. " Proceedings of the Royal Society. 1913. A 89, 1–20 [as excerpted in Henry A. Boorse & Lloyd Motz, The World of the Atom, Vol. 1 (New York: Basic Books, 1966)]. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  19. ^ Rutherford, Ernest. "Collisions of alpha Particles with Light Atoms. IV. An Anomalous Effect in Nitrogen." Philosophical Magazine. 1919. 6th series, 37, 581. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  20. ^ Chadwick, James. (February 27, 1932), "Possible Existence of a Neutron. " Nature. February 27, 1932. Events 1560 - The Treaty of Berwick, which would expel the French from Scotland, is signed by England and the Congregation Year 1932 ( MCMXXXII) was a Leap year starting on Friday of the Gregorian calendar. p. 312. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  21. ^ a b c Bohr, N. "On the constitution of atoms and molecules. " Philosophical Magazine. July 1913. 26, 1-25. Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  22. ^ Schrödinger, Erwin. "Quantisation as an Eigenvalue Problem. " Annalen der Physik.
  23. ^ Mahanti, Subodh. "Erwin Schrödinger: The Founder of Quantum Wave Mechanics. " Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.
  24. ^ Mahanti, Subodh. "Max Born: Founder of Lattice Dynamics. " Retrieved on August 29, 2007. Events 708 - Copper coins are minted in Japan for the first time (Traditional Japanese date: August 10, 708) Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century.

External links

Dictionary

atomic theory

-noun

  1. (physics) The theory that all gross matter is composed of atoms.
  2. (physics) Any of several theories that explain the structure of the atom, and of subatomic particles.
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