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Atom

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Chrono

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Early theories of the structure of matter were not based upon experiments. As scientists began to study the relationship between several physical phenomenon such as electricity, and magnetism they began to develop different models about atomic structure.

Year Scientist(s) Discovery

Greek era Democritus "by convention bitter, by convention sweet, but in reality atoms and void"

1704 Isaac Newton Proposed a mechanical universe with small solid masses in motion.

1803 John Dalton Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.

1832 Michael Faraday Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism.

1859 J. Plucker Built one of the first gas discharge tubes ("cathode ray tube").

1869 Dmitri Mendeleev Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law.

1873 James Clerk Maxwell Proposed electric and magnetic fields filled the void.

1879 Sir William Crookes Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce; impart a negative charge to objects they strike; are deflected by electric fields and magnets to suggest a negative charge; cause pinwheels in their path to spin indicating they have mass.

1886 E. Goldstein Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron.

1894 G.J. Stoney Proposed that electricity was made of discrete negative particles he called electrons ". (Link to info on electrons)

1895 Wilhelm Roentgen Using a CRT he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them "X-rays".

1896 Henri Becquerel While studying the effect of x-rays on photographic film, he discovered some chemicals spontaneously decompose and give off very pentrating rays.

1897 J.J. Thomson Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.

1897 J.J. Thomson Studied "canal rays" and found they were associated with the proton H + .

1898 Rutherford Studied radiations emitted from uranium and thorium and named them alpha and beta.

1898 Marie Sklodowska Curie Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

1900 Soddy Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay.

1900 Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter.

1903 Nagaoka Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle.

1904 Abegg

Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity.

1905 Albert Einstein Published the famous equation E=mc 2

1906 Hans Geiger Developed an electrical device to "click" when hit with alpha particles.

1909 R.A. Millikan Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron.

1911 Ernest Rutherford Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm)gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.

1914 H.G.J. Moseley Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

1919 Aston Discovered the existence of isotopes through the use of a mass spectrograph.

1922 Niels Bohr Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.

1923 de Broglie Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein.

1927 Heisenberg Described atoms by means of formula connected to the frequencies of spectral lines. Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.

1929 Cockcroft / Walton Built an early linear accelerator and bombarded lithium with protons to produce alpha particles

1930 Schrodinger Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.

1930 Paul Dirac Proposed anti-particles . Anderson discovered the anti-electron (positron) in 1932 and Segre/Chamberlain detected the anti-proton in 1955..

1932 James Chadwick Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.

1938 Lise Meitner, Hahn , Strassman Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

1941 - 51 Glenn Seaborg Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table.

1942 Enrico Fermi Conducted the first controlled chain reaction releasing energy from the atoms nucleus.

1950's - New findings/particles Follow this link to current theories about atomic stucture.



wiki atomism

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Atomism is a natural philosophy developed by Leucippus and his student Democritus in the fifth century BC[1]. These atomists theorized that the natural world consists of two fundamental and opposite, indivisible bodies - atom and void. Atoms were reality's very small, indestructible building blocks (Aristotle, Metaphysics, I, 4, 985 b, 10-15). The word atomism derives from the ancient Greek word atomos, meaning that which cannot be cut into smaller pieces (a - tomos (not cuttable) - tomos a conjugate of the Greek verb temnein (to cut)).

The word atomism derives from the ancient Greek word atomos which parses into a-tomos (not cuttable) - tomos being a conjugate of the Greek verb temnein (to cut) - meaning that which cannot be cut into smaller pieces.



Berryman, Sylvia, "Ancient Atomism", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), URL = <http://plato.stanford.edu/archives/fall2008/entries/atomism-ancient/>. Leucippus and Democritus are widely regarded as the first atomists in the Greek tradition. 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. 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 the negation of body. Atoms are by their nature 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. Because 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.

FROM WIKI ATOM ARTICLE

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Origin of modern atomic theory

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Further progress in the understanding of atoms did not occur until the science of chemistry began to develop. In 1661, natural philosopher Robert Boyle published The Sceptical Chymist in which he argued that matter was composed of various combinations of different "corpuscules" or atoms, rather than the classical elements of air, earth, fire and water.[12] In 1789 the term element was defined by the French nobleman and scientific researcher Antoine Lavoisier to mean basic substances that could not be further broken down by the methods of chemistry.[13]

In 1803, English instructor and natural philosopher John Dalton used the concept of atoms to explain why elements always react in a ratio of small whole numbers—the law of multiple proportions—and why certain gases dissolve better in water than others. He proposed that each element consists of atoms of a single, unique type, and that these atoms can join together to form chemical compounds.[14][15] Dalton is considered the orginator of modern atomic theory.[16]

Atomic fission and high energy atomic physics

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In 1938, a student of Rutherford, the German chemist Otto Hahn (along with his pupil and assistant Fritz Strassmann) directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product. He mentioned this decisive experiment of 17 December 1938 (the celebrated "radium-barium-mesothorium-fractionation"), in a letter to his physics colleague Lise Meitner, who had emigrated to Sweden to avoid the anti-Jewish prosecution in Germany. Hahn remarked that the uranium "could not just have burst". Lise Meitner and her nephew Otto Frisch changed the experiment and tried to identify the decay products in an ionization chamber, looking directly for lighter products. This experiment was successful and proved that Hahn's result was the first experimental nuclear fission.[36][37] In 1944, Hahn received the Nobel prize in chemistry in which, despite the efforts of Hahn, the contributions of Meitner and Frisch were not recognized.[38]

In 1938, the German chemist Otto Hahn (a student of Rutherford's) directed neutrons onto uranium atoms expecting to create transuranic elements. Instead, his chemical tests showed barium, a lighter element, as a product. In 1939, his physics colleague Lise Meitner (living in Sweden to avoid anti-Jewish prosecution in Germany) and her nephew Otto Frisch verified that Hahn's result had been the first experimental nuclear fission[36][37]. In 1944, Hahn received the Nobel prize in chemistry in which, despite the efforts of Hahn, the contributions of Meitner and Frisch were not recognized.[38]

The German chemist Otto Hahn, a student of Rutherford, directed neutrons onto uranium atoms expecting to get transuranium elements. Instead, his chemical experiments showed barium as a product. Lise Meitner and her nephew Otto Frisch verified that Hahn's result had been the first experimental nuclear fission.[37][38] In 1944, Hahn received the Nobel prize in chemistry in which, despite the efforts of Hahn, the contributions of Meitner and Frisch were not recognized.[39]


^ Siegfried (2002:42–55). ^ "Lavoisier's Elements of Chemistry". Elements and Atoms. Le Moyne College, Department of Chemistry. Retrieved on 2007-12-18. ^ Wurtz (1881:1–2). ^ Dalton (1808). ^ Patterson, Elizabeth C. (1970). John Dalton and the Atomic Theory. Garden City, New York: Anchor ^ Meitner, Lise; Frisch, Otto Robert (1939). "Disintegration of uranium by neutrons: a new type of nuclear reaction". Nature 143: 239. doi:10.1038/143239a0. ^ Schroeder, M.. "Lise Meitner - Zur 125. Wiederkehr Ihres Geburtstages" (in German). Retrieved on 2009-06-04. ^ Crawford, E.; Lewin Sime, R.; Walker, M. (1997). "A Nobel tale of postwar injustice". Physics Today 50 (9): 26–32. doi:10.1063/1.881933.

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Leucippus and Democritus, founders of ancient atomist theory

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Democritus's Atomic Theory

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Who discovered the atom?

Democritus He discovered Democritus's Atomic Theory, which stated that matter is made up of empty space, and an infinite amount of tiny particles called atomos, or atoms. Several scientist later confirmed his theory.

Source(s):

The little book of scientific theoris, principles and things. by Surendra Verma

The ancient Greek scientist Democritus first talked about the atom. He said that every kind of matter could be broken down to identical particles that cannot be broken down to anything smaller, and he called them atoms (=can't be broken, in Greek).


the big view

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With the work of Leucippus and Democritus ancient Greek philosophy reaches its zenith when the initial question of Thales after the true nature of matter culminated 180 years later in the subtle concept of atoms, which bears an amazing resemblance to the twentieth century's view of chemistry. For this reason, Leucippus and Democritus have undoubtedly deserved the first price for the best guess in antiquity, as far as natural science is concerned. Unfortunately their contemporaries did not share their views with the same enthusiasm.

Leucippus is a very shadowy figure; his exact dates are unknown, some even say he never existed, but it is likely that he was a contemporary of Empedocles (around 440 BC) and that he came either from Miletus or from Elea. Democritus, who was a disciple of Leucippus, is a more certain figure. He was born 460 BC in Abdera in the north of Greece and died at the age of 90 years, after leaving an expansive work elaborating his philosophy including the atomistic theory in great detail. Democritus has written approximately 70 books and hence overshadows his master by far. Unfortunately none of his writings remained intact, but a great deal of what he said has survived in Epicurus.

The atomistic theory began as an endeavor to overcome the odd logical consequences of the Eleatic school. Leucippus and Democritus did not accept the Eleatic hypothesis that "everything is one" and that change and motion is an illusion. Parmenides had said the void is a fiction, because saying the void exists would mean to say there is something that is nothing, which he thought is a contradiction in itself, but he was deceived by thinking of "being" in the sense of "material being". Thinking of the void as real would have overthrown Parmenides' theory, because allowing the void to exist as "space bereft of body" (Aristotle) with adjoining plenums implies the opposite of classical monism.

Overthrowing monism was exactly what Leucippus and Democritus intended. They succeeded elegantly by inventing the concept of atoms, for which they are still known. Democritus began with stating a notion of space that served as its premise. Rather than an attribute of matter that describes its extension, Democritus characterizes space as a receptacle for stationary and moving objects, which -under certain circumstances- can as well be completely empty.

Twenty centuries later, Sir Isaac Newton had set forth the receptacle standpoint from where he developed his mechanics. He had a bitter controversy with Leibniz who held, on somewhat different grounds than Parmenides, that space is a system of relations. Today, we realize that both views about space were inaccurate because space can be without solid matter, but it always contains some form of radiation. We also know that the geometry of space is defined by mass, hence, the concept of space as a property of "what is" is closer to the understanding of contemporary physics, therefore Newton is likely to lose this argument today.

Leucippus and Democritus did not care to refute the Parmenidean paradox about the void, instead they simply ignored it, which proved to be useful, because it let them constructively explain motion and change. Change, they explained, is an observation that does not deceive the senses; change is real, it happens on account of the recombination of more rudimentary substances.

Previous Greek philosophers had already raised this point, but prior to the atomists none of them was able to provide a satisfactory explanation for what "substance" is. It was Leucippus' and Democitus' endeavor to develop a theory that would be consistent with sense perception and -by virtue of logical coherence- not contestable by the Parmenidean arguments.

They held that the nature of things consists of an infinite number of extremely small particles, which they called atoms. Atoms are physically, but not geometrically, indivisible. Democritus described atoms as being indestructible and completely full, i.e. containing no empty space. Because of their indestructibility, atoms are eternal. The notion of the atom itself as an "eternal oneness" may be interpreted as a concession to the Eleatic school.

According to the atomists, nature exists only of two things, namely atoms and the void that surrounds them. Leucippus and Democritus thought that there are many different kinds of atoms, each distinct in shape and size and that all atoms move around in space. Surprisingly they did not deem it necessary to give a reason for the motion of atoms, whereby they avoided the sort of logical mistakes that other philosophers had made. They denied that the motion of atoms is impelled in any way, instead they held that atoms move at random, like in the modern kinetic theory of gases. Democritus illustrated the movement of atoms with an observation he made in nature. He compared it to the movement of motes in a sunbeam when there is no wind.

The moving atoms inevitably collide in space, which in some cases causes them to be deflected like billiard balls, and in other cases, when the shapes of two atoms match in a way that they can interlock, causes them to build clusters upon collision, thereby forming substances which make up the objects of our perception. In this regard, Democritus' idea reveals an interesting parallel to Pythagoras, who said that all things are numbers. Because the characteristics of an atom can be described in numbers, any substance can be expressed as a combination of these numbers.

It is controversial whether the atomists also regarded weight a quality of atoms. It seems they simply neglected weight, although Democritus had mentioned that "the more any indivisible exceeds, the heavier it is". At this point, the atomists entered into what their predecessors had postulated to be the origin of matter, namely water (Thales), air (Anaximenses), fire (Heraclitus) and earth (Empedocles). They said, quite accurately as we know today, that these four elements are not primordial substances, but are composed of atoms like everything else.

Contemporary science has proven the atomists right. The atom concept finally took shape in 20th century's views of physics and chemistry. We know atoms as particles with a small positive nucleus that is surround by clouds of electrons and we know that the size of the entire structure is approximately 1/10,000,000 mm. Of course, the antique notion of atoms seems crude by comparison. The characteristics of being indivisible, indestructible, and massive, which had originally been ascribed atoms, cannot be upheld any longer. Today, we also have a better understanding of the internal structure of atoms, and we know that weight, or better mass, is a significant property of atoms.

Nonetheless, Leucippus and Democritus came closer to the truth than anyone else in the following millennium. They developed a fully mechanistic view of nature in which every material phenomenon is seen a product of the atom collisions. Democritus' theory had no place for the notion of purpose and the intervention of gods in the workings of the world. He even held that mind and soul is formed by the movement of atoms. In this regard, his attitude was genuinely materialistic.

Stanford Encyclopedia of Philosophy

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Democritus

First published Sun Aug 15, 2004

Democritus, known in antiquity as the ‘laughing philosopher’ because of his emphasis on the value of ‘cheerfulness,’ was one of the two founders of ancient atomist theory. He elaborated a system originated by his teacher Leucippus into a materialist account of the natural world. The atomists held that there are smallest indivisible bodies from which everything else is composed, and that these move about in an infinite void space. Of the ancient materialist accounts of the natural world which did not rely on some kind of teleology or purpose to account for the apparent order and regularity found in the world, atomism was the most influential. Even its chief critic, Aristotle, praised Democritus for arguing from sound considerations appropriate to natural philosophy.

1. Life and Works

According to ancient reports, Democritus was born about 460 BCE (thus, he was a younger contemporary of Socrates) and was a citizen of Abdera, although some reports mention Miletus. As well as his associate or teacher Leucippus, Democritus is said to have known Anaxagoras, and to have been forty years younger than the latter (DK 68A1). A number of anecdotes concern his life, but their authenticity is uncertain.

The work of Democritus has survived only in secondhand reports, sometimes unreliable or conflicting. Much of the best evidence is that reported by Aristotle, who regarded him as an important rival in natural philosophy. Aristotle wrote a monograph on Democritus, of which only a few passages quoted in other sources have survived. Democritus seems to have taken over and systematized the views of Leucippus, of whom little is known. Although it is possible to distinguish some contributions as those of Leucippus, the overwhelming majority of reports refer either to both figures, or to Democritus alone; the developed atomist system is often regarded as essentially Democritus'.

2. Atomist Doctrine

Ancient sources describe atomism as one of a number of attempts by early Greek natural philosophers to respond to the challenge offered by Parmenides. Parmenides had argued that it is impossible for there to be change without something coming from nothing. Since the idea that something could come from nothing was generally agreed to be impossible, Parmenides argued that change is merely illusory. In response, Leucippus and Democritus, along with other Presocratic pluralists such as Empedocles and Anaxagoras, developed systems that made change possible by showing that it does not require that something should come to be from nothing. These responses to Parmenides suppose that there are multiple unchanging material principles, which persist and merely rearrange themselves to form the changing world of appearances. In the atomist version, these unchanging material principles are indivisible particles, the atoms: the atomists are said to have taken the idea that there is a lower limit to divisibility to answer Zeno's paradoxes about the impossibility of traversing infinitely divisible magnitudes.

Leucippus

First published Sat Aug 14, 2004

The Greek tradition regarded Leucippus as the founder of atomism in physics. Little is known about him, and his views are hard to distinguish from those of his associate Democritus. He is sometimes said to have been a student of Zeno of Elea, and to have devised the atomist philosophy in order to escape from the problems raised by Parmenides and his followers.

1. Life and Works

Leucippus is variously said to have been born in Elea, Abdera or Miletus (DK 67A1). His dates are unknown, other than that he lived during the fifth century BCE. Diogenes Laertius reports that he was a student of Parmenides' follower Zeno (DK 67A1). Zeno is best known for paradoxes suggesting that motion is impossible because a magnitude can be divided into an infinite number of parts, each of which must be traversed; the fact that atomism is thought to have been formulated in response to these arguments may account for the story that Leucippus was a student of Zeno.

The extent of Leucippus' contribution to the developed atomist theory is unknown. Most reports refer to the views of Democritus alone, or to both atomists together; Epicurus seems even to have denied that there was a philosopher Leucippus (DK 67A2). Aristotle certainly ascribes the foundation of the atomist system to Leucippus. Leucippus is sometimes said to have been the author of a work called the Great World-System; one surviving quotation is said to have come from a work On Mind.

2. Atomist Doctrine

Leucippus is named by most sources as the originator of the theory that the universe consists of two different elements, which he called ‘the full’ or ‘solid,’ and ‘the empty’ or ‘void’. Both the void and the solid atoms within it are thought to be infinite, and between them to constitute the elements of everything. Because little is known of Leucippus' views and his specific contributions to atomist theory, a fuller discussion of the developed atomist doctrine is found in the entry for Democritus.

  • atomism

1. Atomism before Leucippus?

Leucippus (5th c. BCE) is the earliest figure whose commitment to atomism is well attested. He is usually credited with inventing atomism. According to a passing remark by the geographer Strabo, Posidonius (1st c. BCE Stoic philosopher) reported that ancient Greek atomism can be traced back to a figure known as Moschus or Mochus of Sidon, who lived at the time of the Trojan wars. This report was given credence in the seventeenth century: the Cambridge Platonist Henry More traced the origins of ancient atomism back, via Pythagoras and Moschus, to Moses. This theologically motivated view does not seem to claim much historical evidence, however.

In 1877, Tannéry argued that Zeno of Elea's arguments about divisibility must have been formulated in response to a particular view held by some early Pythagoreans. Tannéry's view, which was widely accepted in the early twentieth century, is based on the claim that one of Zeno's paradoxes about the possibility of motion would best make sense if it were attacking an atomist thesis, and thus that the Pythagoreans, who are reported to have talked of monads or unit numbers, must have been atomists of a sort. Tannery's thesis has been thoroughly challenged since then: most scholars instead consider atomism to be one of a number of positions formulated in response to the arguments of Parmenides and Zeno (first half of the fifth century). A fourth-century Pythagorean, Ecphantus, interpreted the Pythagorean monads as indivisible bodies: he is reported to have been sympathetic to atomism of a kind similar to Democritus'. Plato's discussion of the composition of solids from plane surfaces is thought to be based on fourth-century Pythagorean theories.

2. Leucippus and Democritus

Leucippus and Democritus are widely regarded as the first atomists in the Greek tradition. 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. 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 the negation of body. Atoms are by their nature 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. Because 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.

John Dalton, founder of modern atomic theory

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John Dalton's Atomic Theory

John Dalton, the father of modern atomic theory, developed the atomic theory in the early nineteenth century. According to him, all elements are made of atoms...

Though the earliest atomic theories were proposed by Democritus and Aristotle, the first accepted theory was proposed by John Dalton. John Dalton (1766-1844), an English Chemist, Physicist and meteorologist, is honored mainly because of his contribution to modern atomic theory and color blindness. It was Dalton's research studies on the properties of atmosphere and gases in 1803, that made him realize about the particles (later called atoms) and their weight. The same research paper was published in 1805.

John Dalton published the first table on relative atomic weights that included six elements viz. hydrogen, oxygen, carbon, nitrogen, phosphorous and sulfur. He stated the atomic weight of hydrogen to be 1. It was not confirmed as to how he derived the atomic weights. However, his laboratory notebook (dated September 1803) indicated that he found out the relative weights from the studies of the compounds - water, carbon dioxide and ammonia. In his notebook, the elements were represented by symbols. He was the first person to propose the idea of identifying an element by its symbol. Later on, elements are represented by their abbreviations, for example, 'H' is the abbreviation of the element hydrogen.

As per the lecture given by John Dalton in 1803, in the Royal Institution (London), atoms of one element differed from those of other elements by their relative weights. Following are some of the important points, proposed by John Dalton in his atomic theory:

  • All elements are made up of tiny indivisible particles, known as atoms
  • Atoms of the same element are identical with respect to their weights
  • Atoms of different elements are different from each other and can be identified by their relative weights
  • Atoms can neither be divided into smaller particles nor destroyed
  • Chemical reactions occur due to the rearrangement of the atoms
  • Atoms combine in the ratio of whole numbers such as 1:1, 1:2, 2:3 etc.
  • Atoms of two or more different elements combine together to form chemical compounds

Dalton

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Who discovered the atom?

In: History of Science

In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles they called atom, or in Greek "a-tomos". The reason why they assumed this is because nothing can come from nothing. Around 1803, John Dalton (1766-1844) developed the first useful atomic theory of matter. He imagined the atom as a sphere full of an electrically positive substance mixed with negative electron. Then in 1897, Thompson discovered the first component part of the atom: the electron, a particle with a negative electric charge.

Discovery of the Atom

By the 19th century, technology had advanced greatly and many elements had been discovered to work with. Using the available elements scientist such as John Dalton and Amedeo Avogadro forced them to interact with one another. From these interactions they were able to prove the existence of the atom.

Answer

That depends on exactly what you mean by "discovered."

Jainism had a concept of small particles similar to atoms in the 6th millennium BC, and either Democritus or his mentor Leucippus (or possibly both together) independently came up with the idea (and the word "atomos", which is Greek for "uncuttable") in the 5th century BC. However, these were essentially lucky guesses; there was no real scientific basis behind them, so saying these people "discovered" atoms is a pretty big stretch.

The best candidate is probably John Dalton, who in the early 19th century proposed (based this time on experiments) that substances were composed of atoms, and even assigned relative weight values to several types of atom.

Dalton or Rutherford

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Ask A Scientist

Chemistry Archive

Who discovered the atom?

Question: Who discovered the atom? jessica a gancarski Answer 1: A simple question, but deceptively complicated. What does it mean to "discover" something? The first person to propose that matter was made of atoms, and then write it down, was a Greek philosopher named Democritus. But he had no experimental proof of his notion. Then, a number of scientists, starting probably with Newton in the late 1600s, proposed a corpuscular, or atomic, model. But it wasn't until the late 1700s/early 1800s that John Dalton proposed that all matter was made of atoms and actually used it to explain a bunch of experiments that had been done on gases, and to calculate atomic weights of elements. However, he still hadn't PROVED that atoms existed...he just showed that the atomic concept was useful and helped explain a lot of data. Probably the best direct probe of the atom was first done by Rutherford and his student, C.T.R. Wilson, who invented the cloud chamber and used it to show that when thin gold foil is bombarded by helium nuclei (alpha particles), the particles are occasionally deflected by a very large angle, but usually pass straight through. This gave rise to the realization that the gold was composed of atoms, with a tiny nucleus at the middle which could occasionally collide with an alpha particle and send it flying. -prof topper Answer 2: Coupla more comments for ya. I think the Greek concept of the atom was unlike ours: to their minds a pickle was composed of small green sour atoms, a fire of hot light bright atoms, etc. More of an aesthetic than empirical concept. In my opinion they get a little more credit in general for atoms than they deserve. Second, in addition to Dalton's work suggesting the atom because of fixed chemical combining rules, there was the astoundingly successful kinetic theory of gases, a subject of intense interest in the nineteenth century, which relies utterly on gases being made of little bits of flying matter. Names here are Bernoulli (1740s), Joule (1850s), Clausius & Maxwell (1860s), and finally the giant Boltzmann (1870s). Even as late as 1900 the existence of atoms was seriously doubted by able scientists (e.g. Mach), and from the point of view of many the definitive proof is the apparently unique explanation by Einstein in 1905 of "Brownian motion," the incessant jiggling of pollen grains visible under a microscope that is caused by its battering by the invisible molecules. The experiment in 1909 by Geiger and Marsden in the laboratory of Rutherford (alpha particle scattering from gold foil) is usually considered proof of the existence of the nucleus, although of course a nucleus implies an atom too. Answer 3: It should however be pointed out that most scientists utterly rejected the kinetic theory of gases, and that the reputations of all the aforementioned scientists were damaged severely in the eyes of their contemporaries by their espousal of atomic theories. Boltzmann in particular took the rejection of his work particularly hard...in fact, he killed himself. Too bad he didn't wait around a bit longer. I think that you could argue that the early spectroscopic work of Angstrom, Balmer, etc. provided proof of the existence of atoms, although the experiments may not have been properly interpreted at the time. In hindsight, they were probing atomic energy levels. Finally, although the Greek view of "atoms" was certainly not the same as the idea we have today, certainly that particular school was the first to put forth the idea that the microscopic properties give rise to macroscopic properties. Sure, they got the details all wrong, and worked without experimental data. In retrospect, it was a lucky guess. But science is full of lucky guesses, and in my opinion it does no harm to give Democritus credit for his cleverness. Especially since almost noone believed him at the time....often a good sign that one is right. -prof topper



Rutherford, founder of nuclear physics

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  • first experimental proof showing atomic structure
  • atom


In 1909, researchers under the direction of physicist Ernest Rutherford bombarded a sheet of gold foil with alpha rays—by then known to be positively charged helium atoms—and discovered that a small percentage of these particles were deflected through much larger angles than was predicted using Thomson's proposal. Rutherford interpreted the gold foil experiment as suggesting that the positive charge of a heavy gold atom and most of its mass was concentrated in a nucleus at the center of the atom—the Rutherford model.[24] Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS (30 August 1871–19 October 1937) was a New Zealand born British chemist and physicistwho became known as the father of nuclear physics.[1] He discovered that atoms have a small charged nucleus, and thereby pioneered the Rutherford model(or planetary model, which later evolved into the Bohr model or orbital model) of the atom, through his discovery of Rutherford scattering with his gold foil experiment. He was awarded the Nobel Prize in Chemistry in 1908. He is widely credited as splitting the atom in 1917 and leading the first experiment to "split the nucleus" in a controlled manner by two students under his direction, John Cockcroft and Ernest Walton in 1932. In 1907 Rutherford took the chair of physics at the University of Manchester. There along with Hans Geiger and Ernest Marsden he carried out the Geiger–Marsden experiment, which demonstrated the nuclear nature of atoms. It was his interpretation of this experiment that led him to formulate the Rutherford model of the atom—that a very small positively-charged nucleus was orbited by electrons. In 1919 he became the first person to transmute one element into another when he converted nitrogen into oxygen through the nuclear reaction 14N + α → 17O + p. In 1921, while working with Niels Bohr (who postulated that electrons moved in specific orbits), Rutherford theorized about the existence of neutrons, which could somehow compensate for the repelling effect of the positive charges of protons by causing an attractive nuclear force and thus keeping the nuclei from breaking apart. Rutherford's theory of neutrons was proved in 1932 by his associate James Chadwick, who in 1935 was awarded the Nobel Prize in Physics for this discovery.

 
A stylised representation of the Rutherford model of a lithium atom (nuclear structureanachronistic)

The Rutherford model or planetary model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in 1909, which suggested to Rutherford's analysis (1911) that the Plum pudding modelofJ. J. Thomson of the atom was incorrect. Rutherford's new model for the atom, based on the experimental results, had a number of essential modern features, including a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and containing the bulk of the atomic mass (the nucleus of the atom), and a number of tinyelectronscircling around the nucleus like planets around the sun.

Symbolism

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Despite its inaccuracy, the Rutherford model caught the imagination of the public in a way that the more correct Bohr model did not, and has continually been used as a symbol for atoms and atomic energy. Examples of its use over the past century include:

Rutherford model of 1911

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the early 20th century, experiments by Ernest Rutherford established that atoms consisted of a diffuse cloud of negatively charged electrons surrounding a small, dense, positively charged nucleus. Given this experimental data, Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 – electrons orbiting a solar nucleus – however, said planetary-model atom has a technical difficulty. The laws of classical mechanics (i.e. the Larmor formula), predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would gradually spiral inwards, collapsing into the nucleus. This atom model is disastrous, because it predicts that all atoms are unstable.

Also, as the electron spirals inward, the emission would gradually increase in frequency as the orbit got smaller and faster. This would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharges through various low-pressure gasses in evacuated glass tubes had shown that atoms will only emit light (that is, electromagnetic radiation) at certain discrete frequencies.

To overcome this difficulty, Niels Bohr proposed, in 1913, what is now called the Bohr model of the atom. He suggested that electrons could only have certain classical motions.

Proposed changes

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as is

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as suggested

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rationales

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Wikipedia:Naming conventions

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The present convention for articles providing more detail on a given topic is using the{{Main|<toppage>}}and{{Details|<subpage>}} templates, in accordance with Wikipedia:Summary style, and the guidance on how to avoid POV content forks. Such templates are placed under a section header, each instance of these templates providing a link to a subpage.

Occasionally, these subsidiary pages — if they contain content that is only relevant as an elaboration of a shorter paragraph on the main page — can have more complex page names; that is, if they are only intended to be accessed by a link from the main article. For example, Isaac Newton has Isaac Newton's early life and achievements as one of its pages on sub-topics.

However, if a "common name" for such subsidiary page is possible, that is always preferred.

Section 1 Conventions

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If there is an established, universally agreed-upon common name for an event, use that name. Otherwise, create a name using these guidelines. In most cases, the title of the article should contain at least the following two descriptors:

  • Where the incident happened.
  • What happened.

If these descriptors are not sufficient to identify the event unambiguously, a third descriptor should be added:

  • When the incident happened.

The year ("when") should not be used in the title unless other descriptors are insufficient to establish the identity of the incident.


Section 1 Rationale

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Names of articles should be the most commonly used name for the following reasons:

We want to maximize the likelihood of being listed in external search engines, thereby attracting more people to Wikipedia. For example, one pagename is Jimmy Carter and not "James Earl Carter, Jr."; the string "Jimmy Carter" in the page title makes it easier to find: search engines will often give greater weight to the contents of the title than to the body of the page. Since "Jimmy Carter" is the most common form of the name, it will be searched on more often, and having that exact string in our page title will often mean our page shows up higher in other search engines. We want to maximize the incidence that people who make a link guessing the article name, guess correctly; people guessing a different name may think there is no article yet, which may cause duplication. Using a full formal name requires people to know that name, and to type more. We respect our readers and name our articles as they do, just formulating their collective needs.

Redirects help, but give a slightly unattractive "redirected from" announcement at the top of the page. On the other hand, if someone reads or hears "Elizabeth II", and wonders who might be meant by that, the "(Redirected from Elizabeth II)" at the top of the page describing the monarch in question puts the reader at ease that this was the intended queen: the "redirect" message indicates that the system hasn't been playing tricks, and that this was the page to which you were supposed to be led.

Wikipedia:Naming conventions - Use the most easily recognized name (1)

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Generally, article naming should prefer what the greatest number of English speakers would most easily recognize, with a reasonable minimum of ambiguity, while at the same time making linking to those articles easy and second nature.

This is justified by the following principle:

The names of Wikipedia articles should be optimized for readers over editors, and for a general audience over specialists.

Wikipedia determines the recognizability of a name by seeing what verifiable reliable sources in English call the subject.


Other specific conventions (4)

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People (4.35)

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Wikipedia:Naming conventions (people) starts from the idea that names in the format <First name> <Last name> are usually the least problematic as page name for an article on a single person.

The guideline concentrates on these cases where this format is not the most obvious, for example, how to deal with middle names, with Iberian naming customs, with names of people from countries where the surname comes first, with disambiguation (when several people share the same name), etc.

The people NC guideline has absorbed some content previously in Wikipedia:Naming conventions (common names) (e.g., abbreviations in names of people), or separate topics on this page, that were not mentioned in specific guidelines until now (e.g., Spanish family names).

Wikipedia:Summary style

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Shortcut

Wikipedia articles tend to grow in a way which lends itself to the natural creation of new articles. The text of any article consists of a sequence of related but distinct subtopics. When there is enough text in a given subtopic to merit its own article, that text can be summarized from the present article and a link provided to the more detailed article.

The length of a given Wikipedia article tends to grow as people add information to it. This cannot go on forever: very long articles would cause problems. So we must move information out of articles periodically. In general, information should not be removed from Wikipedia: that would defeat the purpose of the contributions. So we must create new articles to hold the excised information.

Size

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Further information: Wikipedia:Article size

Articles over a certain size may not cover their topic in a way that's readable and easy to navigate. Opinions vary as to what counts as an ideal length; judging the appropriate size depends on the topic and whether it easily lends itself to being split up.

Basic technique

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Further information: Wikipedia:Splitting

Longer articles are split into sections, each about several good-sized paragraphs long. Subsectioning can increase this amount. Ideally many of those sections will eventually provide summaries of separate articles on the subtopic covered in that section (a Main article or similar link would be below the section title—see {{Main}}, {{Details}},...) Each article on a subtopic is an encyclopedic article in its own right and contains its own lead section(which will be quite similar to the summary in its 'parent' article).

Other specifics

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Avoiding unnecessary splits

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Shortcut

Editors are cautioned to not immediately split articles if the new article would meet neither the general notability criterion nor the specific notability criteria for their topic. Instead, editors are encouraged to instead work on further developing the main article first, locating sources of real-world coverage that apply both to the main topic and the subtopic. Through this process, it may become evident that subtopics or groups of subtopics can demonstrate their own notability and help justifying splitting off into their own article. If information can be trimmed, merged, or removed, these steps should be undertaken first before the new article is created.

Always mention in the edit summary when splitting

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Whenever you break up a page, please note the split (including the page names between double square brackets) in the edit summary. Add {{Main}} to the top of the section that is being split out, to indicate where the main article for that section is.

Avoidance of POV forks

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See also Wikipedia:Content forking

In applying summary style to articles, care must be taken to avoid a POV fork (that is, a split which results in the original article and/or the spin-off violating NPOV), and/or a difference in approach between the summary and the spin-off, etc. See:Wikipedia:Content forking, Article spinouts - "Summary style" articles.

Where an article is long, and has lots of subtopics with their own articles, try to balance parts of the main page. Do not put overdue weight into one part of an article at the cost of other parts. In shorter articles, if one subtopic has much more text than another subtopic, that may be an indication that that subtopic should have its own page, with only a summary presented on the main page.

Keeping summary articles and detailed articles synchronised

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Sometimes editors will add details to a summary section without adding those facts to the more detailed article. To keep articles synchronized, editors should first add any new material to the appropriate places in the detailed article, and if appropriate, summarize the material in the summary section. In other cases, the detailed article may grow considerably in scope, and the summary section will need to be re-written to do it justice. These problems may be tagged with {{Sync}}.

Naming conventions for subarticles

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Subarticles (not to be confused with subpages) of a "Summary style" article are one of a few instances where an exception to the common names principle for article naming is sometimes acceptable, see Wikipedia:Naming conventions#Subsidiary articles.

Subarticle navigation

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Unless all subarticles of a "Summary style" article are truly compliant to the common names principle, it is a good idea to provide a navigational template to connect the subarticles among themselves, and with the "Summary style" main article.

Example of such navigational template, used on subarticles of the "Isaac Newton" article: {{IsaacNewtonSegments}}

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See also: Wikipedia:Verifiability and Wikipedia:Citing sources

"Summary style" is an excellent technique to give more structure to long lists of references: for example the "World War II" summary style article portrayed above could have a "Further reading" section which treats the history of World War II as a whole, while the subarticles are provided with references which treat the specifics of each of these subtopics, e.g. books on World War II in the Pacific region are used as references in the Pacific War article. Similarly, External linksrelevant to the subtopic should go in the subtopic article and external links which treat the history of World War II as a whole belong in the summary style article.

There is no need to repeat all the references for the subtopics in the main "Summary style" article, unless they are required to support a specific point. The policy on sources, Wikipedia:Verifiability, says that sources must be provided for any material that is challenged or likely to be challenged, and for all quotations.

When adding material to a section in the summary style, however, it is important to ensure that the material is present in the sub-article with a reference. This also imposes additional burden in maintaining Wikipedia articles, as it is important to ensure that the broad article and its sub-articles remain consistent.

Lead section

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See also: Wikipedia:Lead section

For the planned paper Wikipedia 1.0, one recommendation is that the paper version of articles will be the lead section of the web version. Summary style and news style can help make a concise intro that works stand-alone.

Rationale

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This style of organizing articles is somewhat related to news style except it focuses on topics instead of articles. The idea is to summarize and distribute information across related articles in a way that can serve readers who want varying amounts of detail. Thus giving readers the ability to zoom to the level of detail they need and not exhausting those who need a primer on a whole topic.

This is more helpful to the reader than a very long article that just keeps growing, eventually reaching book-length. Summary style is accomplished by not overwhelming the reader with too much text up front by summarizing main points and going into more detail on particular points (sub-topics) in separate articles. What constitutes 'too long' is largely based on the topic, but generally 30KB of prose is the starting point where articles may be considered too long. Articles that go above this have a burden of proof that extra text is needed to efficiently cover its topic and that the extra reading time is justified.

Sections that are less important for understanding the topic will tend to be lower in the article (this is news style applied to sections). Often this is difficult to do for articles on history or that are otherwise chronologically based unless there is some type of analysis section. Organizing in this way is important due to the fact that many readers will not finish reading the article.

Levels of desired details

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Shortcut

Wikipedia is not divided into a macropædia, micropædia, and concise versions as is the Encyclopædia Britannica — we must serve all three user types in the same encyclopedia. Summary style is based on the premise that information about a topic should not all be contained in a single article since different readers have different needs;

  • many readers need just a quick summary of the topic's most important points (lead section),
  • others need a moderate amount of info on the topic's more important points (a set of multi-paragraph sections), and
  • some readers need a lot of detail on one or more aspects of the topic (links to full-sized separate articles).

The parent article should have general summary information and the more detailed summaries of each subtopic should be in daughter articles and in articles on specific subjects. This can be thought of as layering inverted pyramids where the reader is shown the tip of a pyramid (the lead section) for a topic and within that article any section may have a{{main|<subpage name>}} or similar link to a full article on the topic summarized in that section (see Yosemite National Park#History and History of the Yosemite area for an example using twofeatured articles). The summary in a section at the parent article will often be at least twice as long as the lead section in the daughter article. The daughter article in turn can also serve as a parent article for its specific part of the topic. And so on until a topic is very thoroughly covered. Thus by navigational choices several different types of readers get the amount of detail they want.

See also

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Wikipedia:Lead section

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Introductory text

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Shortcut

Provide an accessible overview

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The lead section should briefly summarize the most important points covered in an article in such a way that it can stand on its own as a concise version of the article. It is even more important here than for the rest of the article that the text be accessible. Consideration should be given to creating interest in reading the whole article. (See news style and summary style.) Accordingly, editors should avoid lengthy paragraphs and over-specific descriptions, especially if they are not central to the article as a whole.

Relative emphasis

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In general, the relative emphasis given to material in the lead should reflect its relative importance to the subject according to reliable sources. Significant information should not appear in the lead if it is not covered in the remainder of the article, although specific facts, such as birthdates, titles, or scientific designations will often appear in the lead only, as may certain quotations. This should not be taken to exclude information from the lead, but to include it in both the lead and body: in a well-constructed article, the relative emphasis given to information in the lead will be reflected in the rest of the text. Do not tease the reader by hinting at startling facts without describing them.

Opening paragraph

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Shortcut

The first paragraph of the introductory text needs to unambiguously define the topic for the reader, without being overly specific. It should establish the context in which the topic is being considered, by supplying the set of circumstances or facts that surround it. If appropriate, give the location and time context. Also, establish the boundaries of the content of the article (for example List of environmental issues is only about the effects of human activity).

First sentence

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The article should begin with a short declarative sentence, answering two questions for the nonspecialist reader: "What (or who) is the subject?" and "Why is this subject notable?"[2]

  • If possible, the page title should be the subject of the first sentence.[3] However, if the article title is merely descriptive—such as Electrical characteristics of dynamic loudspeakers—the title does not need to appear verbatim in the main text. Similarly, where an article title is of the type "List of ...", a clearer and more informative introduction to the list is better than verbatim repetition of the title.
  • When the page title is used as the subject of the first sentence, it may appear in a slightly different form, and it may include variations, including synonyms.[4] Similarly, if the title has a parenthetical disambiguator, the disambiguator should be omitted in the text.[5]
  • If its subject is amenable to definition, then the first sentence should give a concise definition: where possible, one that puts the article in context for the nonspecialist. Similarly, if the subject is a term of art, provide the context as early as possible.[6]
  • If the article is about a fictional character or place, say so.[7]
  • If the page is a list, do not introduce the list as "This is a list of X" or "This list of Xs...". (SeeFormat of the first sentence below).

Notes

  1. ^ Berryman, Sylvia, "Ancient Atomism", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), URL =<http://plato.stanford.edu/archives/fall2008/entries/atomism-ancient/>
  2. ^ For example:

    Amalie Emmy Noether, IPA: [ˈnøːtɐ], (23 March 1882 – 14 April 1935) was a German mathematician known for her groundbreaking contributions to abstract algebra and her contributions to theoretical physics.

    This example not only tells the reader that the subject was a mathematician, it also indicates her field of expertise and work she did outside of it. The years of her birth and death provide time context. The reader who goes no further in this article already knows when she lived, what work she did, and why she is notable. (Wikipedia:Manual of Style (biographies) has more on the specific format for biography articles.)

  3. ^ For example:

    This Manual of Style is a style guide containing ...

    not

    This style guide, known as the Manual of Style, contains ...
  4. ^ For example, in the article "United Kingdom":

    The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, theUK, or Britain, is a sovereign island country located off the northwestern coast of continental Europe.
  5. ^ Thus, the article Egg (food) should start like this:

    An egg is an ovum produced by ...

    Not like this:

    An egg (food) is an ovum produced by ...
  6. ^ For example, instead of:

    A trusted third party is an entity that facilitates interactions between two parties who both trust the third party.

    write:

    In cryptography, a trusted third party is an entity that facilitates interactions between two parties who both trust the third party.
  7. ^ For example:

    Homer Simpson is a fictional character in The Simpsons.

Format of the first sentence

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See also: WP:MOSBOLD
Shortcuts

As a general rule, the first (and only the first) appearance of the article's subject should be as early as possible in the first sentence and should be in boldface:

The Solar System consists of the Sun and those celestial objects bound to it bygravity.

The article's subject is usually the same as the page title, but not always. In lists (including outlines, indexes, and glossaries), the subject is generally preceded by the article type (such as "List of"). The article type should not be presented as the subject of the article, only the part after it should. For example, in Outline of Africa, the first sentence of the lead should describe Africa, and present it in bold – not Outline of Africa (the article is not about outlines of Africa, it is presenting information about Africa in outline form).

If the title of a page is descriptive it does not need to appear verbatim in the main text, and even if it does it should not be in boldface. So, for example, Electrical characteristics of dynamic loudspeakers begins with:

A dynamic loudspeaker driver's chief electrical characteristic is its electrical impedanceversusfrequency.

If the subject of the page is normally italicized (for example, a work of art, literature, album, or ship) then its first mention should be both bold and italic text; if it is usually surrounded by quotation marks, the title should be bold but the quotation marks should not:

Las Meninas (Spanish for The Maids of Honour) is a 1656 painting by Diego Velázquez, ...

"Yesterday" is a pop song originally recorded by The Beatles for their 1965 album Help!.

If the subject of the page has a common abbreviation or more than one name, the abbreviation (in parentheses) and each additional name should be in boldface on its first appearance. But do not boldface foreign names not normally used in English, or variations included only to show etymology. Foreign names (including transcriptions) that use the Roman alphabet should be italicized if they are not bolded; those written in other alphabets (such as Cyrillic) should not.

Sodium hydroxide (NaOH), also known as lye, caustic soda and (incorrectly, according to IUPAC nomenclature) sodium hydrate, is ...

Chernivtsi Oblast ([Чернівецька область, Chernivets’ka oblast’] Error: {{Langx}}: text has italic markup (help)) is an oblast (province) in western Ukraine, bordering on Romania and Moldova.

Inuit (plural; the singular Inuk means "man" or "person") is a general term for a group of culturally similarindigenous peoples inhabiting the Arctic regions . . .

Use as few links as possible before and in the bolded title. Thereafter, words used in a title may be linked to provide more detail:

Arugam Bay is a bay situated on the Indian Ocean in the dry zone of Sri Lanka's southeast coast.


Usage in first sentence

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See also: Wikipedia:Naming conventions (geographic names)

In articles about places, people, literary and artistic works, scientific principles and concepts, and other subjects, the title can be followed in the first line by one or two alternative names in parentheses. The following are examples of names that may be included parenthetically, but this is not mandatory, and inclusion should reflect consensus.


example of date in title

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