query: who proposed that atomic nucleus is positively charged

pos: Atomic nucleus forces which bind it together, is called nuclear physics. The nucleus was discovered in 1911, as a result of Ernest Rutherford's efforts to test Thomson's "plum pudding model" of the atom. The electron had already been discovered earlier by J.J. Thomson himself. Knowing that atoms are electrically neutral, Thomson postulated that there must be a positive charge as well. In his plum pudding model, Thomson suggested that an atom consisted of negative electrons randomly scattered within a sphere of positive charge. Ernest Rutherford later devised an experiment with his research partner Hans Geiger and with help of Ernest Marsden, that

pos: Atom to the positively charged nucleus by the attraction created from opposite electric charges. If an atom has more or fewer electrons than its atomic number, then it becomes respectively negatively or positively charged as a whole; a charged atom is called an ion. Electrons have been known since the late 19th century, mostly thanks to J.J. Thomson; see history of subatomic physics for details. Protons have a positive charge and a mass 1,836 times that of the electron, at . The number of protons in an atom is called its atomic number. Ernest Rutherford (1919) observed that nitrogen under alpha-particle

pos: Alpha particle in its center, making the positive charge dense enough to deflect any positively charged alpha particles that came close to what was later termed the nucleus. Prior to this discovery, it was not known that alpha particles were themselves atomic nuclei, nor was the existence of protons or neutrons known. After this discovery, J.J. Thomson's "plum pudding" model was abandoned, and Rutherford's experiment led to the Bohr model (named for Niels Bohr) and later the modern wave-mechanical model of the atom. Rutherford went on to use alpha particles to accidentally produce what he later understood as a directed nuclear transmutation

neg: 20th century in science model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar) - the gravitational force of the solar system is mathematically akin to the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons. In 1913, Henry Moseley, working from Van den Broek's earlier idea, introduces concept of atomic number to fix inadequacies of Mendeleev's periodic table, which had been based on atomic weight. The peak of Frederick Soddy's career in radiochemistry was in 1913 with his formulation of the

neg: Atomic nucleus elementary particles, called quarks, that are held in association by the nuclear strong force in certain stable combinations of hadrons, called baryons. The nuclear strong force extends far enough from each baryon so as to bind the neutrons and protons together against the repulsive electrical force between the positively charged protons. The nuclear strong force has a very short range, and essentially drops to zero just beyond the edge of the nucleus. The collective action of the positively charged nucleus is to hold the electrically negative charged electrons in their orbits about the nucleus. The collection of negatively charged electrons

neg: Atomic nucleus Atomic nucleus The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron in 1932, models for a nucleus composed of protons and neutrons were quickly developed by Dmitri Ivanenko and Werner Heisenberg. An atom is composed of a positively-charged nucleus, with a cloud of negatively-charged electrons surrounding it, bound together by electrostatic force. Almost all of the mass of an atom is located in the nucleus, with a very small contribution

neg: Effective atomic number an atom as being 'stacked' by energy outside the nucleus; the lowest energy electrons (such as the 1s and 2s electrons) occupy the space closest to the nucleus, and electrons of higher energy are located further from the nucleus. The binding energy of an electron, or the energy needed to remove the electron from the atom, is a function of the electrostatic interaction between the negatively charged electrons and the positively charged nucleus. In Iron, atomic number 26, for instance, the nucleus contains 26 protons. The electrons that are closest to the nucleus will 'see' nearly all of them. However,

neg: Beta decay in the Feynman diagram on the right), this is caused by the conversion of the negatively charged (− e) down quark to the positively charged (+ e) up quark by emission of a boson; the boson subsequently decays into an electron and an electron antineutrino: In decay, or "positron emission", the weak interaction converts an atomic nucleus into a nucleus with atomic number decreased by one, while emitting a positron () and an electron neutrino (). decay generally occurs in proton-rich nuclei. The generic equation is: This may be considered as the decay of a proton inside the nucleus to

neg: Neutron physics that occurred in the first half of the 20th century, leading ultimately to the atomic bomb in 1945. In the 1911 Rutherford model, the atom consisted of a small positively charged massive nucleus surrounded by a much larger cloud of negatively charged electrons. In 1920, Rutherford suggested that the nucleus consisted of positive protons and neutrally-charged particles, suggested to be a proton and an electron bound in some way. Electrons were assumed to reside within the nucleus because it was known that beta radiation consisted of electrons emitted from the nucleus. Rutherford called these uncharged particles "neutrons", by the

neg: Henry Moseley by Ernest Rutherford and Antonius van den Broek of the atom, with a positively charged nucleus surrounded by negatively charged electrons in which the atomic number is understood to be the exact physical number of positive charges (later discovered and called protons) in the central atomic nuclei of the elements. Moseley mentioned the two scientists above in his research paper, but he did not actually mention Bohr, who was rather new on the scene then. Simple modification of Rydberg's and Bohr's formulas were found to give theoretical justification for Moseley's empirically derived law for determining atomic numbers. X-ray spectrometers are

neg: Atomic orbital fundamental defect in the theory even at its conception, namely that a classical charged object cannot sustain orbital motion because it is accelerating and therefore loses energy due to electromagnetic radiation. Nevertheless, the Saturnian model turned out to have more in common with modern theory than any of its contemporaries. In 1909, Ernest Rutherford discovered that the bulk of the atomic mass was tightly condensed into a nucleus, which was also found to be positively charged. It became clear from his analysis in 1911 that the plum pudding model could not explain atomic structure. In 1913 as Rutherford's post-doctoral student,

neg: Ion carbon to hydrogen bond are called "organic ions". If the charge in an organic ion is formally centred on a carbon, it is termed a "carbocation" (if positively charged) or "carbanion" (if negatively charged). Monatomic ions are formed by the gain or loss of electrons to the valence shell (the outer-most electron shell) in an atom. The inner shells of an atom are filled with electrons that are tightly bound to the positively charged atomic nucleus, and so do not participate in this kind of chemical interaction. The process of gaining or losing electrons from a neutral atom or molecule

neg: Atomic radius The way the atomic radius varies with increasing atomic number can be explained by the arrangement of electrons in shells of fixed capacity. The shells are generally filled in order of increasing radius, since the negatively charged electrons are attracted by the positively charged protons in the nucleus. As the atomic number increases along each row of the periodic table, the additional electrons go into the same outermost shell; whose radius gradually contracts, due to the increasing nuclear charge. In a noble gas, the outermost shell is completely filled; therefore, the additional electron of next alkali metal will go into

neg: Atomic radius and electrons because opposite charges attract, and more protons creates a stronger charge. The greater attraction draws the electrons closer to the protons, decreasing the size of the particle. Therefore, atomic radius decreases. Down the groups, atomic radius increases. This is because there are more energy levels and therefore a greater distance between protons and electrons. In addition, electron shielding causes attraction to decrease, so remaining electrons can go farther away from the positively charged nucleus. Therefore, size (atomic radius) increases. The following table summarizes the main phenomena that influence the atomic radius of an element: The electrons in the

neg: Fundamental interaction greater than 10 femtometers, the strong force is practically unobservable. Moreover, it holds only inside the atomic nucleus. After the nucleus was discovered in 1908, it was clear that a new force, today known as the nuclear force, was needed to overcome the electrostatic repulsion, a manifestation of electromagnetism, of the positively charged protons. Otherwise, the nucleus could not exist. Moreover, the force had to be strong enough to squeeze the protons into a volume whose diameter is about 10 m, much smaller than that of the entire atom. From the short range of this force, Hideki Yukawa predicted that

neg: Introduction to quantum mechanics distinction between the study of individual particles in quantum dynamics and the study of massed particles in classical physics. By the dawn of the 20th century, evidence required a model of the atom with a diffuse cloud of negatively charged [[electron]]s surrounding a small, dense, positively charged [[Atomic nucleus|nucleus]]. These properties suggested a model in which electrons circle around the nucleus like planets orbiting a sun. However, it was also known that the atom in this model would be unstable: according to classical theory, orbiting electrons are undergoing centripetal acceleration, and should therefore give off electromagnetic radiation, the loss of

neg: Hydrogen atom Hydrogen atom A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe. In everyday life on Earth, isolated hydrogen atoms (called "atomic hydrogen") are extremely rare. Instead, hydrogen tends to combine with other atoms in compounds, or with itself to form ordinary (diatomic) hydrogen gas, H. "Atomic hydrogen" and "hydrogen atom" in ordinary English use have overlapping, yet distinct, meanings. For example, a

neg: Rutherford model or 100) might be exactly the same. A month after Rutherford's paper appeared, the proposal regarding the exact identity of atomic number and nuclear charge "was" made by Antonius van den Broek, and later confirmed experimentally within two years, by Henry Moseley. These are the key indicators- After Rutherford's discovery, scientists started to realize that the atom is not ultimately a single particle, but is made up of far smaller subatomic particles. Subsequent research determined the exact atomic structure which led to Rutherford's gold foil experiment. Scientists eventually discovered that atoms have a positively charged nucleus (with an exact atomic

neg: Electronegativity other electrons present in the atomic shells (the more electrons an atom has, the farther from the nucleus the valence electrons will be, and as a result the less positive charge they will experience—both because of their increased distance from the nucleus, and because the other electrons in the lower energy core orbitals will act to shield the valence electrons from the positively charged nucleus). The opposite of electronegativity is electropositivity: a measure of an element's ability to donate electrons. The term "electronegativity" was introduced by Jöns Jacob Berzelius in 1811, though the concept was known even before that and

neg: Hydrogen atom (non relativistic) hydrogen atom was solved for the first time within Feynman's path integral formulation of quantum mechanics. This work greatly extended the range of applicability of Feynman's method. Hydrogen atom A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe. In everyday life on Earth, isolated hydrogen atoms (called "atomic hydrogen") are extremely rare. Instead, hydrogen tends to combine with other atoms

neg: Strong interaction but it comes in three types (±red, ±green, ±blue) rather than one, which results in a different type of force, with different rules of behavior. These rules are detailed in the theory of quantum chromodynamics (QCD), which is the theory of quark-gluon interactions. Before the 1970s, physicists were uncertain as to how the atomic nucleus was bound together. It was known that the nucleus was composed of protons and neutrons and that protons possessed positive electric charge, while neutrons were electrically neutral. By the understanding of physics at that time, positive charges would repel one another and the positively charged

neg: Atom or positive charge, respectively, and it is called an ion. The electrons of an atom are attracted to the protons in an atomic nucleus by this electromagnetic force. The protons and neutrons in the nucleus are attracted to each other by a different force, the nuclear force, which is usually stronger than the electromagnetic force repelling the positively charged protons from one another. Under certain circumstances, the repelling electromagnetic force becomes stronger than the nuclear force, and nucleons can be ejected from the nucleus, leaving behind a different element: nuclear decay resulting in nuclear transmutation. The number of protons in

neg: History of chemistry a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar) - the gravitational force of the solar system is mathematically akin to the attractive Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons. In the Bohr model, however, electrons orbit the nucleus in orbits that have a set size and energy - the energy levels are said to be "quantized", which means that only certain orbits with certain radii are allowed; orbits in between simply don't exist.

neg: Coulomb's law Coulomb was able to calculate the force between the balls and derive his inverse-square proportionality law. Coulomb's law states that: Coulomb's law can also be stated as a simple mathematical expression. The scalar and vector forms of the mathematical equation are In this way, the verification is limited to measuring the distance between the charges and check that the division approximates the theoretical value. Coulomb's law holds even within atoms, correctly describing the force between the positively charged atomic nucleus and each of the negatively charged electrons. This simple law also correctly accounts for the forces that bind atoms together

neg: Neutron capture are also used in reprocessing nuclear fuel rods, when it is necessary to separate uranium and plutonium, and sometimes thorium. Neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, which are repelled electrostatically. Neutron capture plays an important role in the cosmic nucleosynthesis of heavy elements. In stars it can proceed in two ways: as a rapid (r-process) or a slow process (s-process). Nuclei of masses

neg: Franck–Hertz experiment fundamental assumption of the Bohr model concerns the possible binding energies of an electron to the nucleus of an atom. The atom can be ionized if a collision with another particle supplies at least this binding energy. This frees the electron from the atom, and leaves a positively charged ion behind. There is an analogy with satellites orbiting the earth. Every satellite has its own orbit, and practically any orbital distance, and any satellite binding energy, is possible. Since an electron is attracted to the positive charge of the atomic nucleus by a similar force, so-called "classical" calculations suggest that

neg: Subatomic particle the prerequisite basics of Newtonian mechanics, a series of statements and equations in "Philosophiae Naturalis Principia Mathematica", originally published in 1687. The negatively charged electron has a mass equal to of that of a hydrogen atom. The remainder of the hydrogen atom's mass comes from the positively charged proton. The atomic number of an element is the number of protons in its nucleus. Neutrons are neutral particles having a mass slightly greater than that of the proton. Different isotopes of the same element contain the same number of protons but differing numbers of neutrons. The mass number of an isotope

neg: Neutron capture Neutron capture Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, which are repelled electrostatically. Neutron capture plays an important role in the cosmic nucleosynthesis of heavy elements. In stars it can proceed in two ways: as a rapid (r-process) or a slow process (s-process). Nuclei of masses greater than 56 cannot be formed by thermonuclear reactions (i.e. by nuclear fusion), but can be formed by neutron capture.

neg: Mott scattering section formula is the mathematical description of the scattering of a high energy electron beam from an atomic nucleus-sized positively charged point in space. The Mott scattering is the theoretical diffraction pattern produced by such a mathematical model. It is used as the beginning point in calculations in electron scattering diffraction studies. The equation for the Mott cross section includes an inelastic scattering term to take into account the recoil of the target proton or nucleus. It also can be corrected for relativistic effects of high energy electrons, and for their magnetic moment. When an experimentally found diffraction pattern deviates

neg: Chemical bond that are orbiting the nucleus and the positively charged protons in the nucleus attract each other. An electron positioned between two nuclei will be attracted to both of them, and the nuclei will be attracted toward electrons in this position. This attraction constitutes the chemical bond. Due to the matter wave nature of electrons and their smaller mass, they must occupy a much larger amount of volume compared with the nuclei, and this volume occupied by the electrons keeps the atomic nuclei in a bond relatively far apart, as compared with the size of the nuclei themselves. In general, strong

neg: Photoinduced charge separation Photoinduced charge separation Photoinduced charge separation is the process of an electron in an atom or molecule, being excited to a higher energy level by the absorption of a photon and then leaving the atom or molecule to a nearby electron acceptor. An atom consists of a positively charged nucleus orbited by electrons. The nucleus consists of uncharged neutrons and positively charged protons. Electrons are negatively charged. In the early part of the twentieth century Ernest Rutherford suggested that the electrons orbited the dense central nucleus in a manner analogous to planets orbiting the sun. The centripetal force required to

neg: Atomic nucleus two protons, or two neutrons, or a proton + neutron (the deuteron) can exhibit bosonic behavior when they become loosely bound in pairs, which have integer spin. In the rare case of a hypernucleus, a third baryon called a hyperon, containing one or more strange quarks and/or other unusual quark(s), can also share the wave function. However, this type of nucleus is extremely unstable and not found on Earth except in high energy physics experiments. The neutron has a positively charged core of radius ≈ 0.3 fm surrounded by a compensating negative charge of radius between 0.3 fm and 2

neg: Antimatter-catalyzed nuclear pulse propulsion tradeoff between the two demands. By injecting a small amount of antimatter into a subcritical mass of fuel (typically plutonium or uranium) fission of the fuel can be forced. An anti-proton has a negative electric charge just like an electron, and can be captured in a similar way by a positively charged atomic nucleus. The initial configuration, however, is not stable and radiates energy as gamma rays. As a consequence, the anti-proton moves closer and closer to the nucleus until they eventually touch, at which point the anti-proton and a proton are both annihilated. This reaction releases a tremendous amount

neg: Atomic nucleus involved the deflection of alpha particles (helium nuclei) directed at a thin sheet of metal foil. He reasoned that if Thomson's model were correct, the positively charged alpha particles would easily pass through the foil with very little deviation in their paths, as the foil should act as electrically neutral if the negative and positive charges are so intimately mixed as to make it appear neutral. To his surprise, many of the particles were deflected at very large angles. Because the mass of an alpha particle is about 8000 times that of an electron, it became apparent that a very

neg: Plum pudding model Plum pudding model The plum pudding model is one of several scientific models of the atom. First proposed by J. J. Thomson in 1904 soon after the discovery of the electron, but before the discovery of the atomic nucleus, the model represented an attempt to consolidate the known properties of atoms at the time: 1) electrons are negatively-charged particles and 2) atoms are neutrally-charged. In this model, atoms were known to consist of negatively charged electrons. Though Thomson called them "corpuscles", they were more commonly called "electrons" as G. J. Stoney proposed in 1894. At the time, atoms were known

neg: Yukawa potential Yukawa potential with e equal to 1 everywhere. This can be interpreted as saying that the photon mass "m" is equal to 0. In interactions between a meson field and a fermion field, the constant "g" is equal to the gauge coupling constant between those fields. In the case of the nuclear force, the fermions would be a proton and another proton or a neutron. Prior to Hideki Yukawa's 1935 paper, physicists struggled to explain the results of James Chadwick's atomic model, which consisted of positively charged protons and neutrons packed inside of a small nucleus, with a radius on

neg: Chemistry made up of positively charged protons and uncharged neutrons (together called nucleons), while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is approximately 1,836 times that of an electron, yet the radius of an atom is about 10,000 times that of its nucleus. The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s), coordination

neg: Stern–Gerlach experiment prevalent model for describing the atom was the Bohr model, which described electrons as going around the positively charged nucleus only in certain discrete atomic orbitals or energy levels. Since the electron was quantized to be only in certain positions in space, the separation into distinct orbits was referred to as space quantization. The Stern–Gerlach experiment was meant to test the Bohr–Sommerfeld hypothesis that the direction of the angular momentum of a silver atom is quantized. Note that the experiment was performed several years before Uhlenbeck and Goudsmit formulated their hypothesis of the existence of the electron spin. Even though

neg: Nuclear reaction large repository of reaction rates is the REACLIB database, as maintained by the Joint Institute for Nuclear Astrophysics. In the initial collision which begins the reaction, the particles must approach closely enough so that the short range strong force can affect them. As most common nuclear particles are positively charged, this means they must overcome considerable electrostatic repulsion before the reaction can begin. Even if the target nucleus is part of a neutral atom, the other particle must penetrate well beyond the electron cloud and closely approach the nucleus, which is positively charged. Thus, such particles must be first accelerated

neg: Charged particle Charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can be the electrons and protons themselves, as well as other elementary particles, like positrons. It may also be an atomic nucleus devoid of electrons, such as an alpha particle, a helium nucleus. Neutrons have no charge. A plasma is a collection of charged particles, atomic nuclei and separated electrons, but can also be a gas containing a significant proportion of charged particles. Plasma

neg: Hydrogen-like atom that we can consider almost all of these states to be already filled. If one of these negative-energy states is not filled, this manifests itself as though there is an electron which is "repelled" by a positively-charged nucleus. This prompted Dirac to hypothesize the existence of positively-charged electrons, and his prediction was confirmed with the discovery of the positron. The Dirac equation with a simple Coulomb potential generated by a point-like non-magnetic nucleus was not the last word, and its predictions differ from experimental results as mentioned earlier. More accurate results include the Lamb shift (radiative corrections arising from quantum

neg: Heavy Rydberg system fully shield the positively charged nucleus, another electron brought into close proximity will feel an attractive force. While this classical description is nice for getting a feel for the interactions involved, it is an oversimplification; many other atoms have a greater electron affinity than hydrogen. In general the process of forming a negative ion is driven by the filling of atomic electron shells to form a lower energy configuration. Only a small number of molecules have been used to produce heavy Rydberg systems although in principle any atom with a positive electron affinity can bind with a positive ion. Species

neg: Quantum chemistry Schrödinger equation can only be obtained for the hydrogen atom (though exact solutions for the bound state energies of the hydrogen molecular ion have been identified in terms of the generalized Lambert W function). Since all other atomic, or molecular systems, involve the motions of three or more "particles", their Schrödinger equations cannot be solved exactly and so approximate solutions must be sought. The foundation of quantum mechanics and quantum chemistry is the wave model, in which the atom is a small, dense, positively charged nucleus surrounded by electrons. The wave model is derived from the wave function, a set

neg: Tandem accelerator Tandem accelerator Conventionally, positively charged ions are accelerated because this is the polarity of the atomic nucleus. However, if one wants to use the same static electric potential twice to accelerate ions, then the polarity of the ions' charge must change from anions to cations or vice versa while they are inside the conductor where they will feel no electric force. It turns out to be simple to remove, or strip, electrons from an energetic ion. One of the properties of ion-interaction with matter is the exchange of electrons, which is a way the ion can lose energy by depositing

neg: Charged particle is called the fourth state of matter because its properties are quite different from solids, liquids and gases. Charged particle In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can be the electrons and protons themselves, as well as other elementary particles, like positrons. It may also be an atomic nucleus devoid of electrons, such as an alpha particle, a helium nucleus. Neutrons have no charge. A plasma is a collection of charged particles, atomic

neg: Noble gas compound they are less strongly attracted to the positively charged nucleus. This results in an ionization energy low enough to form stable compounds with the most electronegative elements, fluorine and oxygen, and even with less electronegative elements such as nitrogen and carbon under certain circumstances. When the family of noble gases was first identified at the end of the nineteenth century, none of them was observed to form any compounds and it was initially believed that they were all "inert gases" (as they were then known) which could not form compounds. With the development of atomic theory in the early twentieth

neg: Tandem accelerator same style of conventional electrostatic accelerators based on the method of charging the terminal. An outline of the tandem accelerator system, with animation Tandem accelerator Conventionally, positively charged ions are accelerated because this is the polarity of the atomic nucleus. However, if one wants to use the same static electric potential twice to accelerate ions, then the polarity of the ions' charge must change from anions to cations or vice versa while they are inside the conductor where they will feel no electric force. It turns out to be simple to remove, or strip, electrons from an energetic ion. One

neg: Low-energy ion scattering positively charged primary ions and the nuclei of surface atoms. The interaction potential is given as: Where formula_7 and formula_8 are the atomic numbers of the primary ion and surface atom, respectively, formula_9 is the elementary charge, formula_10 is the interatomic distance, and formula_11 is the screening function. formula_11 accounts for the interference of the electrons orbiting each nucleus. In the case of MEIS and RBS, this potential can be used to calculate the Rutherford scattering cross section (see Rutherford scattering) formula_13: As shown at right, formula_14 represents a finite region for an incoming particle, while formula_15 represents the solid

neg: Effective atomic number Effective atomic number Effective atomic number has two different meanings: one that is the effective nuclear charge of an atom, and one that calculates the average atomic number for a compound or mixture of materials. Both are abbreviated Z. The effective atomic number Z, (sometimes referred to as the effective nuclear charge) of an atom is the number of protons that an electron in the element effectively 'sees' due to screening by inner-shell electrons. It is a measure of the electrostatic interaction between the negatively charged electrons and positively charged protons in the atom. One can view the electrons in

neg: Spin–orbit interaction Spin–orbit interaction In quantum physics, the spin–orbit interaction (also called spin–orbit effect or spin–orbit coupling) is a relativistic interaction of a particle's spin with its motion inside a potential. A key example of this phenomenon is the spin–orbit interaction leading to shifts in an electron's atomic energy levels, due to electromagnetic interaction between the electron's magnetic dipole, its orbital motion, and the electrostatic field of the positively charged nucleus. This phenomenon is detectable as a splitting of spectral lines, which can be thought of as a Zeeman effect product of two relativistic effects: the apparent magnetic field seen from the

neg: Bohr model quantum mechanics (1925) is often referred to as the old quantum theory. In 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 rapidly

neg: Nuclide example of a [[table of nuclides]]:Black – stable (all are primordial)Red – primordial radioactiveOther – radioactive, with decreasing stability from orange to white]] Atomic nuclei consist of protons and neutrons bound together by the [[residual strong force]]. Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart, reducing the electrostatic repulsion between the protons, and they exert the attractive nuclear force on each other and on protons. For this reason, one or more neutrons are necessary for two or more protons to be bound

neg: Isotope chemical properties (again with deuterium and tritium being the primary exceptions). The vibrational modes of a molecule are determined by its shape and by the masses of its constituent atoms; so different isotopologues have different sets of vibrational modes. Because vibrational modes allow a molecule to absorb photons of corresponding energies, isotopologues have different optical properties in the infrared range. Atomic nuclei consist of protons and neutrons bound together by the residual strong force. Because protons are positively charged, they repel each other. Neutrons, which are electrically neutral, stabilize the nucleus in two ways. Their copresence pushes protons slightly apart,

neg: Atomic nucleus "small nut") inside a watery type of fruit (like a peach). In 1844, Michael Faraday used the term to refer to the "central point of an atom". The modern atomic meaning was proposed by Ernest Rutherford in 1912. The adoption of the term "nucleus" to atomic theory, however, was not immediate. In 1916, for example, Gilbert N. Lewis stated, in his famous article "The Atom and the Molecule", that "the atom is composed of the "kernel" and an outer atom or "shell"" The nucleus of an atom consists of neutrons and protons, which in turn are the manifestation of more

neg: Hantaro Nagaoka paper in which the atomic nucleus is proposed. However, other details of the model were incorrect. In particular, electrically charged rings would be unstable due to repulsive disruption. Nagaoka himself abandoned his proposed model in 1908. Rutherford and Niels Bohr would present the more viable Bohr model in 1913. Nagaoka later did research in spectroscopy and other fields. In 1909, he published a paper on the inductance of solenoids. In 1929 he became the first person to describe meteor burst communications. Hantaro Nagaoka Nagaoka was born in Nagasaki, Japan and educated at Tokyo University. After graduating with a degree in

neg: Electroscope occurs because of induced polarization of the atoms inside the pith ball. All matter consists of electrically charged particles located close together; each atom consists of a positively charged nucleus with a cloud of negatively charged electrons surrounding it. The pith is a nonconductor, so the electrons in the ball are bound to atoms of the pith and are not free to leave the atoms and move about in the ball, but they can move a little within the atoms. See diagram at right. If, for example, a positively charged object "(B)" is brought near the pith ball "(A)", the

neg: Carbocation Carbocation A carbocation ( /karbɔkətaɪː'jɔ̃/) is an ion with a positively charged carbon atom. Among the simplest examples are the methenium , methanium and vinyl cations. Occasionally, carbocations that bear more than one positively charged carbon atom are also encountered (e.g., ethylene dication ). Until the early 1970s, all carbocations were called "carbonium ions". In present-day chemistry, a carbocation is any ion with a positively charged carbon atom, classified in two main categories according to the coordination number of the charged carbon: three in the carbenium ions and five in the carbonium ions. This nomenclature was proposed by G. A.

neg: P-ANCA P-ANCA p-ANCA, or MPO-ANCA, or perinuclear anti-neutrophil cytoplasmic antibodies, are antibodies that stain the material around the nucleus of a neutrophil. They are a special class of anti-neutrophil cytoplasmic antibodies. This pattern occurs because the vast majority of the antigens targeted by ANCAs are highly cationic (Positively charged) at pH 7.00. During ethanol (pH ~7.0 in water) fixation, antigens which are more cationic migrate and localize around the nucleus, attracted by its negatively charged DNA content. Antibody staining therefore results in fluorescence of the region around the nucleus. p-ANCAs stain the perinuclear region by binding to specific targets. By far

neg: Hydrogen ion the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions. A hydrogen atom is made up of a nucleus with charge +1, and a single electron. Therefore, the only positively charged ion possible has charge +1. It is noted H. Depending on the isotope in question, the hydrogen cation has different names: In addition, the ions produced by the reaction of these cations with water as well as their hydrates are called hydrogen ions: Zundel cations and Eigen cations play an important role in proton diffusion according to the Grotthuss mechanism. In

neg: Nuclear shell model Nuclear shell model In nuclear physics and nuclear chemistry, the nuclear shell model is a model of the atomic nucleus which uses the Pauli exclusion principle to describe the structure of the nucleus in terms of energy levels. The first shell model was proposed by Dmitry Ivanenko (together with E. Gapon) in 1932. The model was developed in 1949 following independent work by several physicists, most notably Eugene Paul Wigner, Maria Goeppert Mayer and J. Hans D. Jensen, who shared the 1963 Nobel Prize in Physics for their contributions. The shell model is partly analogous to the atomic shell model

neg: Proton nuclei are composed of two or more protons and various numbers of neutrons. The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms (which he called "protyles"), based on a simplistic interpretation of early values of atomic weights (see Prout's hypothesis), which was disproved when more accurate values were measured. In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases. However, since particles

neg: Geiger–Marsden experiment ages earlier. Like most scientific models, Rutherford's atomic model was neither perfect nor complete. According to classical Newtonian physics, it was in fact impossible. Accelerating charged particles radiate electromagnetic waves, so an electron orbiting an atomic nucleus in theory would spiral into the nucleus as it loses energy. To fix this problem, scientists had to incorporate quantum mechanics into Rutherford's model. Geiger–Marsden experiment The Geiger–Marsden experiment(s) (also called the Rutherford gold foil experiment) was a landmark series of experiments by which scientists discovered that every atom contains a nucleus where all of its positive charge and most of its mass

neg: Chemistry: A Volatile History hope they would enter the nucleus. Unfortunately, this was very unlikely because both alpha particles and nuclei are positively charged – the alpha particles could never overcome the electrostatic repulsion of the nucleus. Fermi reasoned that because neutrons carried no electric charge, they would have a much better chance of penetrating the nucleus of a uranium atom. So Fermi set about firing neutrons at uranium. Fermi thought that this, coupled with his knowledge of beta decay, whereby an unstable nucleus attempts stabilisation by converting one neutron to a proton and ejecting a newly formed electron, would result in an element

neg: Channelling (physics) center of the plane, they will be attracted again, so negatively charged particles tend to follow the direction of one crystalline plane. Because the crystalline plane has a high density of atomic electrons and nuclei, the channeled particles eventually suffer a high angle Rutherford scattering or energy-losses in collision with electrons and leave the channel. This is called the "dechannelling" process. Positively charged particles like protons and positrons are instead repelled from the nuclei of the plane, and after entering the space between two neighboring planes, they will be repelled from the second plane. So positively charged particles tend to

neg: Nuclear fission of the atom in which a very small, dense and positively charged nucleus of protons (the neutron had not yet been discovered) was surrounded by orbiting, negatively charged electrons (the Rutherford model). Niels Bohr improved upon this in 1913 by reconciling the quantum behavior of electrons (the Bohr model). Work by Henri Becquerel, Marie Curie, Pierre Curie, and Rutherford further elaborated that the nucleus, though tightly bound, could undergo different forms of radioactive decay, and thereby transmute into other elements. (For example, by alpha decay: the emission of an alpha particle—two protons and two neutrons bound together into a particle

neg: Oppenheimer–Phillips process the positively charged target nucleus, it experiences a charge polarization where the "proton-end" faces away from the target and the "neutron-end" faces towards the target. The fusion proceeds when the binding energy of the neutron and the target nucleus exceeds the binding energy of the deuteron and a proton is then repelled from the new, heavier, nucleus. Explanation of this effect was published by J. Robert Oppenheimer and Melba Phillips in 1935, considering experiments with the Berkeley cyclotron showing that some elements became radioactive under deuteron bombardment. During the O-P process, the deuteron's positive charge is spatially polarized, and collects

neg: Antonius van den Broek periodic table was contained in his paper published in "Nature" on July 20, 1911, just one month after Rutherford published the results of his experiments that showed the existence of a small charged nucleus in an atom (see Rutherford model). However, Rutherford's original paper noted only that the charge on the nucleus was large, on the order of about half of the atomic weight of the atom, in whole number units of hydrogen mass. Rutherford on this basis made the tentative suggestion that atomic nuclei are composed of numbers of helium nuclei, each with a charge corresponding to half of

neg: Molecular orbital orbitals, respectively, formula_5 and formula_6 are the atomic wavefunctions from atoms a and b, respectively, and formula_7 and formula_8 are adjustable coefficients. These coefficients can be positive or negative, depending on the energies and symmetries of the individual atomic orbitals. As the two atoms become closer together, their atomic orbitals overlap to produce areas of high electron density, and, as a consequence, molecular orbitals are formed between the two atoms. The atoms are held together by the electrostatic attraction between the positively charged nuclei and the negatively charged electrons occupying bonding molecular orbitals. When atomic orbitals interact, the resulting molecular

neg: Ionization energy atom, as follows (note that the derivation uses Gaussian units). Consider an electron of charge "-e" and an atomic nucleus with charge "+Ze", where "Z" is the number of protons in the nucleus. According to the Bohr model, if the electron were to approach and bond with the atom, it would come to rest at a certain radius "a". The electrostatic potential "V" at distance "a" from the ionic nucleus, referenced to a point infinitely far away, is: formula_1 Since the electron is negatively charged, it is drawn inwards by this positive electrostatic potential. The energy required for the electron

neg: Enrico Fermi induce radioactivity with Rasetti's polonium-beryllium neutron source. Neutrons had no electric charge, and so would not be deflected by the positively charged nucleus. This meant that they needed much less energy to penetrate the nucleus than charged particles, and so would not require a particle accelerator, which the Via Panisperna boys did not have. Fermi had the idea to resort to replacing the polonium-beryllium neutron source with a radon-beryllium one, which he created by filling a glass bulb with beryllium powder, evacuating the air, and then adding 50 mCi of radon gas, supplied by Giulio Cesare Trabacchi. This created a

neg: Target peptide via interaction with the KDEL receptor in the Golgi apparatus. If the signal is KKXX, the retention mechanism to the ER will be similar but the protein will be transmembranal. A "nuclear localization signal" (NLS) is a target peptide that directs proteins to the nucleus and is often a unit consisting of five basic, positively charged amino acids. The NLS normally is located anywhere on the peptide chain. A "nuclear export signal" (NES) is a target peptide that directs proteins from the nucleus back to the cytosol. It often consists of several hydrophobic amino acids (often leucine) interspaced by 2-3

neg: Atom model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. Until these experiments, atomic number was not known to be a physical and experimental quantity. That it is equal to the atomic nuclear charge remains the accepted atomic model today. Chemical bonds between atoms were now explained, by Gilbert Newton Lewis in 1916, as the interactions between their constituent electrons. As the chemical properties of the elements were known to largely repeat themselves according to the periodic law, in 1919 the American chemist

neg: Molecular orbital theory together. An anti-bonding orbital concentrates electron density "behind" each nucleus (i.e. on the side of each atom which is farthest from the other atom), and so tends to pull each of the two nuclei away from the other and actually weaken the bond between the two nuclei. Electrons in non-bonding orbitals tend to be associated with atomic orbitals that do not interact positively or negatively with one another, and electrons in these orbitals neither contribute to nor detract from bond strength. Molecular orbitals are further divided according to the types of atomic orbitals they are formed from. Chemical substances will

neg: Nuclear localization sequence Nuclear localization sequence A nuclear localization signal "or" sequence (NLS) is an amino acid sequence that 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different nuclear localized proteins may share the same NLS. An NLS has the opposite function of a nuclear export signal (NES), which targets proteins out of the nucleus. These types of NLSs can be further classified as either monopartite or bipartite. The major structural differences between the two is that the

neg: Paul Moskowitz "coffee cup on the car" patent along with over one thousand other patents. According to the "Wall Street Journal", "The Google spokesman declined to comment on the purchase price." While working at the University of Grenoble in France, Paul Moskowitz and French Physicist Maurice Lombardi published an empirical relation that has come to be called the Moskowitz-Lombardi rule or ML rule. The rule helps give nuclear physicists insight into the complex structure of the atomic nucleus which may contain two hundred or more individual protons and neutrons. A charged atomic nucleus with non-zero spin produces a magnetic field whose strength

neg: KIAA1211L alpha helixes, 8.9% beta sheets, and 17.9% turns. The high number of turns is consistent with the fact that KIAA1211L is proline rich. The KIAA1211L protein is predicted to be located in the nucleus. The orthologs, including the elephant shark, horse, rock dove, and chimp, are also predicted to be located in the nucleus. The nuclear location signal is located on amino acids 25-43 which is depicted in both the conceptual translation and schematic figures. . This signal is conserved throughout the orthologs. Additionally, this location (amino acids 24-43) is positively charged, probably due to the high amount of lysine

neg: Nuclear binding energy uranium or plutonium—into smaller fragments, and that is what nuclear power reactors do. An example that illustrates nuclear binding energy is the nucleus of C (carbon-12), which contains 6 protons and 6 neutrons. The protons are all positively charged and repel each other, but the nuclear force overcomes the repulsion and causes them to stick together. The nuclear force is a close-range force (it is strongly attractive at a distance of 1.0 fm and becomes extremely small beyond a distance of 2.5fm), and virtually no effect of this force is observed outside the nucleus. The nuclear force also pulls neutrons

neg: Target peptide other amino acids. Many proteins are known to constantly shuttle between the cytosol and nucleus and these contain both NESs and NLSs. The nucleolus within the nucleus can be targeted with a sequence called a "nucleolar localization signal" (abbreviated NoLS or NOS). The "mitochondrial targeting signal" is a 10-70 amino acid long peptide that directs a newly synthesized protein to the mitochondria. It is found at the N-terminus end consists of an alternating pattern of hydrophobic and positively charged amino acids to form what is called an amphipathic helix. Mitochondrial targeting signals can contain additional signals that subsequently target the

neg: Phospholipid scramblase import sequence lacks a continuous stretch of positively charged residues, and it is enriched in hydrophobic residues. Thus, Scramblase can transport negatively charged phospholipids from the inside of the cell to the outside of the cell. The importin structure is composed of many alpha helices that integrate the protein into membranes. The role of importin is to move proteins such as scramblase into the nucleus. Recent findings suggest that PLSCR3 is involved in regulation of biosynthesis of cardiolipin in mitochondria, and its overexpression in cultured cells resulted in increased cardiolipin synthase, activity. As cardiolipin is synthesized in the luminal side

neg: Atmospheric escape through electric force field acceleration. Stellar EUV and XUV photoionize molecular and atomic species in the upper atmosphere, producing free electrons. The electrons are less massive than their parent ions, and as a result are more easily accelerated up to and beyond the escape velocity of the planet, leaving the ionosphere of Venus and flowing out into the stellar wind. This charge separation between the escaping, low-mass electrons and significantly heavier, positively-charged ions sets up a polarization electric field. That electric field, in turn, acts to pull the positively charged ions along behind the escaping electrons, out of the atmosphere.

neg: Helion (chemistry) chain reaction in stellar fusion. Helion (chemistry) A helion is a short name for the naked nucleus of helium, a doubly positively charged "helium ion". In practice, "helion" refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other stable isotope of helium, helium-4 isotope, which consists of two protons and two neutrons, is specifically called an alpha particle. This particle is emitted in the decay of tritium, an isotope of hydrogen: According to CODATA, the mass of a helion particle is 5.006 412 700(62) × 10 kg. Helions are

neg: Helion (chemistry) Helion (chemistry) A helion is a short name for the naked nucleus of helium, a doubly positively charged "helium ion". In practice, "helion" refers specifically to the nucleus of the helium-3 isotope, consisting of two protons and one neutron. The nucleus of the other stable isotope of helium, helium-4 isotope, which consists of two protons and two neutrons, is specifically called an alpha particle. This particle is emitted in the decay of tritium, an isotope of hydrogen: According to CODATA, the mass of a helion particle is 5.006 412 700(62) × 10 kg. Helions are intermediate products in the proton-proton

neg: Histone deacetylase I HDACs, HDAC 1, 2, and 3 are found primarily in the nucleus, whereas HDAC8 is found in both the nucleus and the cytoplasm, and is also membrane-associated. Class II HDACs (HDAC4, 5, 6, 7 9, and 10) are able to shuttle in and out of the nucleus, depending on different signals. HDAC6 is a cytoplasmic, microtuble-associated enzyme. HDAC6 deacetylates tubulin, Hsp90, and cortactin, and forms complexes with other partner proteins, and is, therefore, involved in a variety of biological processes. Histone tails are normally positively charged due to amine groups present on their lysine and arginine amino acids. These

neg: Niels Bohr Niels Bohr Niels Henrik David Bohr (; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. Bohr was also a philosopher and a promoter of scientific research. Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. Although the Bohr model has been supplanted

neg: Atom majority of atoms combine to form various compounds, including water, salt, silicates and oxides. Atoms can also combine to create materials that do not consist of discrete molecules, including crystals and liquid or solid metals. This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter. While isotopes with atomic numbers higher than lead (82) are known to be radioactive, an "island of stability" has been proposed for some elements with atomic numbers above 103. These superheavy elements may have a nucleus that is relatively stable against radioactive decay. The most likely

neg: Karl P. Cohen to work for Standard Oil Development Company to advise on nuclear energy. Edward Teller’s autobiography "Memoirs" reflects positively on Cohen and Urey's centrifuge method for producing U-235 when he writes: “What if we had the atomic bomb a year earlier? The easiest and least expensive method of separating isotopes, a method used throughout the world today, is based on a centrifuge procedure that Harold Urey proposed in 1940. General Groves chose the diffusion method instead. Karl Cohen, Urey’s able assistant during that period, believes that Groves’ decision delayed the atomic bomb by a year. “If Dr. Cohen is right, atomic

neg: Lipofectamine neutral co-lipid (helper lipid). The DNA-containing liposomes (positively charged on their surface) can fuse with the negatively charged plasma membrane of living cells, due to the neutral co-lipid mediating fusion of the liposome with the cell membrane, allowing nucleic acid cargo molecules to cross into the cytoplasm for replication or expression. In order for a cell to express a transgene, the nucleic acid must reach the nucleus of the cell to begin transcription. However, the transfected genetic material may never reach the nucleus in the first place, instead being disrupted somewhere along the delivery process. In dividing cells, the material

neg: Antimatter tests of Lorentz violation in Physical Review Letters in 1999. The antihydrogen atom is the antimatter counterpart of the hydrogen atom. It has a negatively charged antiproton at the nucleus that attracts a positively charged positron orbiting around it. The spectral lines of hydrogen have frequencies determined by the energy differences between the quantum-mechanical orbital states of the electron. These lines have been studied in thousands of spectroscopic experiments and are understood in great detail. The quantum mechanics of the positron orbiting an antiproton in the antihydrogen atom is expected to be very similar to that of the hydrogen atom. In fact, conventional physics

neg: Nuclear shell model "cloud" of alpha particles. Nuclear shell model In nuclear physics and nuclear chemistry, the nuclear shell model is a model of the atomic nucleus which uses the Pauli exclusion principle to describe the structure of the nucleus in terms of energy levels. The first shell model was proposed by Dmitry Ivanenko (together with E. Gapon) in 1932. The model was developed in 1949 following independent work by several physicists, most notably Eugene Paul Wigner, Maria Goeppert Mayer and J. Hans D. Jensen, who shared the 1963 Nobel Prize in Physics for their contributions. The shell model is partly analogous to

neg: Anharmonicity we may replace "F" by its linear approximation "F"="F'(0)*(x-x)" at zero displacement. The approximating function "F" is linear, so it will describe simple harmonic motion. Further, this function "F" is accurate when "x-x" is small. For this reason, anharmonic motion can be approximated as harmonic motion as long as the oscillations are small. There are many systems throughout the physical world that can be modeled as anharmonic oscillators in addition to the nonlinear mass-spring system. For example, an atom, which consists of a positively charged nucleus surrounded by a negatively charged electronic cloud, experiences a displacement between the center of

neg: Nuclide Nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons "Z", its number of neutrons "N", and its nuclear energy state. The word "nuclide" was proposed by Truman P. Kohman in 1947. Kohman originally suggested "nuclide" as referring to a "species of atom characterized by the constitution of its nucleus" defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus. A nuclide is a species of an atom with

neg: Atom deuterium in the Universe, and perhaps some of the beryllium and boron. Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons. Where the temperature is much higher than ionization potential, the matter exists in the form of plasma—a gas of positively charged ions (possibly, bare nuclei) and electrons. When the temperature drops below the ionization potential, atoms become statistically favorable. Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang—an epoch called recombination, when

neg: Taft equation acid and base catalyzed mechanisms, both of which proceed through a tetrahedral intermediate. In the base catalyzed mechanism the reactant goes from a neutral species to negatively charged intermediate in the rate determining (slow) step, while in the acid catalyzed mechanism a positively charged reactant goes to a positively charged intermediate. Due to the similar tetrahedral intermediates, Taft proposed that under identical conditions any steric factors should be nearly the same for the two mechanisms and therefore would not influence the ratio of the rates. However, because of the difference in charge buildup in the rate determining steps it was

neg: Charge radius Charge radius The rms charge radius is a measure of the size of an atomic nucleus, particularly of a proton or a deuteron. It can be measured by the scattering of electrons by the nucleus and also inferred from the effects of finite nuclear size on electron energy levels as measured in atomic spectra. The problem of defining a radius for the atomic nucleus is similar to the problem of atomic radius, in that neither atoms nor their nuclei have definite boundaries. However, the nucleus can be modeled as a sphere of positive charge for the interpretation of electron scattering

neg: Rutherford scattering (the pudding). If the plum-pudding model were correct, the positive "pudding", being more spread out than in the correct model of a concentrated nucleus, would not be able to exert such large coulombic forces, and the alpha particles should only be deflected by small angles as they pass through. However, the intriguing results showed that around 1 in 8000 alpha particles were deflected by very large angles (over 90°), while the rest passed through with little deflection. From this, Rutherford concluded that the majority of the mass was concentrated in a minute, positively-charged region (the nucleus) surrounded by electrons. When

neg: Enriched uranium processes have been investigated or are under development. Separation of Isotopes by Laser Excitation (SILEX) is well advanced and licensed for commercial operation in 2012. "Atomic vapor laser isotope separation" employs specially tuned lasers to separate isotopes of uranium using selective ionization of hyperfine transitions. The technique uses lasers tuned to frequencies that ionize U atoms and no others. The positively charged U ions are then attracted to a negatively charged plate and collected. "Molecular laser isotope separation" uses an infrared laser directed at UF, exciting molecules that contain a U atom. A second laser frees a fluorine atom, leaving

neg: Dipole the molecule into a net negative part and a net positive part. Consider a collection of "N" particles with charges "q" and position vectors r. For instance, this collection may be a molecule consisting of electrons, all with charge −"e", and nuclei with charge "eZ", where "Z" is the atomic number of the "i" th nucleus. The dipole observable (physical quantity) has the quantum mechanical dipole operator: Notice that this definition is valid only for non-charged dipoles, i.e. total charge equal to zero. To a charged dipole we have the next equation: where formula_3 is the center of mass of

neg: History of physics and Pierre coined the term "radioactivity" to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel's forms of radiation with electrons and the element helium. Rutherford identified and named two types of radioactivity and in 1911 interpreted experimental evidence as showing that the atom consists of a dense, positively charged nucleus surrounded by negatively charged electrons. Classical theory, however, predicted that this structure should be unstable. Classical theory had also failed to explain successfully two other experimental results that appeared in the late 19th century. One of

neg: Voltaic pile to the evolution of hydrogen gas from the copper or silver electrode. The modern, atomic understanding of a cell with zinc and copper electrodes separated by an electrolyte is the following. When the cell is providing an electrical current through an external circuit, the metallic zinc at the surface of the zinc anode is oxidised and dissolves into the electrolyte as electrically charged ions (Zn), leaving 2 negatively charged electrons () behind in the metal: This reaction is called oxidation. While zinc is entering the electrolyte, two positively charged hydrogen ions (H) from the electrolyte accept two electrons at the

neg: Robotic spacecraft the propellant atom becoming a positively charged atom. The positively charged ions are guided to pass through positively charged grids that contains thousands of precise aligned holes are running at high voltages. Then, the aligned positively charged ions accelerates through a negative charged accelerator grid that further increases the speed of the ions up to 90,000 mph. The momentum of these positively charged ions provides the thrust to propel the spacecraft forward. The advantage of having this kind of propulsion is that it is incredibly efficient in maintaining constant velocity, which is needed for deep-space travel. However, the amount of

neg: Aufbau principle to the nucleus and feel on average a less strongly screened nuclear charge. A periodic table in which each row corresponds to one value of "n + ℓ" was suggested by Charles Janet in 1927. In 1936, the German physicist Erwin Madelung proposed his empirical rules for the order of filling atomic subshells, based on knowledge of atomic ground states determined by the analysis of atomic spectra, and most English-language sources therefore refer to the Madelung rule. Madelung may have been aware of this pattern as early as 1926. In 1962 the Russian agricultural chemist V.M. Klechkowski proposed the first