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130-470: The SuperKEKB design reuses many components from KEKB. Under normal operation, SuperKEKB collides electrons at 7 GeV with positrons at 4 GeV (compared to KEKB at 8 GeV and 3.5 GeV respectively). The centre-of-momentum energy of the collisions is therefore at the mass of the Υ(4S) resonance (10.58 GeV/c). The accelerator will also perform short runs at energies of other Υ resonances , in order to obtain samples of other B mesons and baryons. The asymmetry in

260-440: A chemical equation . While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons. The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism . A chemical reaction can be envisioned to take place in

390-404: A de Broglie wave in the manner of light . That is, under the appropriate conditions, electrons and other matter would show properties of either particles or waves. The corpuscular properties of a particle are demonstrated when it is shown to have a localized position in space along its trajectory at any given moment. The wave-like nature of light is displayed, for example, when a beam of light

520-432: A subatomic particle with a negative one elementary electric charge . Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton . Quantum mechanical properties of the electron include an intrinsic angular momentum ( spin ) of

650-648: A charged droplet of oil from falling as a result of gravity. This device could measure the electric charge from as few as 1–150 ions with an error margin of less than 0.3%. Comparable experiments had been done earlier by Thomson's team, using clouds of charged water droplets generated by electrolysis, and in 1911 by Abram Ioffe , who independently obtained the same result as Millikan using charged microparticles of metals, then published his results in 1913. However, oil drops were more stable than water drops because of their slower evaporation rate, and thus more suited to precise experimentation over longer periods of time. Around

780-467: A chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often laboratory glassware . Chemical reactions can result in

910-470: A chemical transformation is the rearrangement of electrons in the chemical bonds between atoms. It can be symbolically depicted through a chemical equation , which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. (When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay .) The type of chemical reactions

1040-490: A circumference of 3016 m with four straight sections and experimental halls in the centre of each, named "Tsukuba", "Oho", "Fuji", and "Nikko". The Belle II experiment is located at the single interaction point in Tsukuba Hall. The target luminosity for SuperKEKB is 6.5×10 cms, this is 30 times larger than the luminosity at KEKB . The improvement is mostly due to a so-called 'nano-beam' scheme, originally proposed for

1170-412: A dense core called the atomic nucleus surrounded by a space occupied by an electron cloud . The nucleus is 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

1300-535: A directed beam in a vacuum in a mass spectrometer . Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry. Some molecules contain one or more unpaired electrons, creating radicals . Most radicals are comparatively reactive, but some, such as nitric oxide (NO) can be stable. The "inert" or noble gas elements ( helium , neon , argon , krypton , xenon and radon ) are composed of lone atoms as their smallest discrete unit, but

1430-410: A fourth state of matter in which the mean free path of the particles is so long that collisions may be ignored. In 1883, not yet well-known German physicist Heinrich Hertz tried to prove that cathode rays are electrically neutral and got what he interpreted as a confident absence of deflection in electrostatic, as opposed to magnetic, field. However, as J. J. Thomson explained in 1897, Hertz placed

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1560-494: A friction that slows the electron. This force is caused by a back-reaction of the electron's own field upon itself. Photons mediate electromagnetic interactions between particles in quantum electrodynamics . An isolated electron at a constant velocity cannot emit or absorb a real photon; doing so would violate conservation of energy and momentum . Instead, virtual photons can transfer momentum between two charged particles. This exchange of virtual photons, for example, generates

1690-801: A fundamental level. For example, chemistry explains aspects of plant growth ( botany ), the formation of igneous rocks ( geology ), how atmospheric ozone is formed and how environmental pollutants are degraded ( ecology ), the properties of the soil on the Moon ( cosmochemistry ), how medications work ( pharmacology ), and how to collect DNA evidence at a crime scene ( forensics ). Chemistry has existed under various names since ancient times. It has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in

1820-560: A half-integer value, expressed in units of the reduced Planck constant , ħ . Being fermions , no two electrons can occupy the same quantum state , per the Pauli exclusion principle . Like all elementary particles, electrons exhibit properties of both particles and waves : They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neutrons and protons because electrons have

1950-429: A lower mass and hence a longer de Broglie wavelength for a given energy. Electrons play an essential role in numerous physical phenomena, such as electricity , magnetism , chemistry , and thermal conductivity ; they also participate in gravitational , electromagnetic , and weak interactions . Since an electron has charge, it has a surrounding electric field ; if that electron is moving relative to an observer,

2080-464: A model of the electron – the Dirac equation , consistent with relativity theory, by applying relativistic and symmetry considerations to the hamiltonian formulation of the quantum mechanics of the electro-magnetic field. In order to resolve some problems within his relativistic equation, Dirac developed in 1930 a model of the vacuum as an infinite sea of particles with negative energy, later dubbed

2210-399: A new world record for the highest instantaneous luminosity for a colliding-beam accelerator: 2.22×10 cms. (On June 21, 2020, SuperKEKB broke its own record and achieved an instantaneous luminosity of 2.40×10 cms.) The previous world record of 2.14×10 cms was achieved by LHC in 2018. Electron The electron ( e , or β in nuclear reactions) is

2340-411: A number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like

2470-456: A particle with a positive charge, such as the proton, and a repulsive force on a particle with a negative charge. The strength of this force in nonrelativistic approximation is determined by Coulomb's inverse square law . When an electron is in motion, it generates a magnetic field . The Ampère–Maxwell law relates the magnetic field to the mass motion of electrons (the current ) with respect to an observer. This property of induction supplies

2600-424: A particular substance per volume of solution , and is commonly reported in mol/ dm . In addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase

2730-405: A pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds , such that the structure

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2860-553: A single electron. This prohibition against more than one electron occupying the same quantum energy state became known as the Pauli exclusion principle . The physical mechanism to explain the fourth parameter, which had two distinct possible values, was provided by the Dutch physicists Samuel Goudsmit and George Uhlenbeck . In 1925, they suggested that an electron, in addition to the angular momentum of its orbit, possesses an intrinsic angular momentum and magnetic dipole moment . This

2990-482: A solution that determined the location of an electron over time, this wave equation also could be used to predict the probability of finding an electron near a position, especially a position near where the electron was bound in space, for which the electron wave equations did not change in time. This approach led to a second formulation of quantum mechanics (the first by Heisenberg in 1925), and solutions of Schrödinger's equation, like Heisenberg's, provided derivations of

3120-609: A substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws . Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure , phase, as well as their chemical compositions . They can be analyzed using the tools of chemical analysis , e.g. spectroscopy and chromatography . Scientists engaged in chemical research are known as chemists . Most chemists specialize in one or more sub-disciplines. Several concepts are essential for

3250-437: A surplus of the charge carrier, and which situation was a deficit. Between 1838 and 1851, British natural philosopher Richard Laming developed the idea that an atom is composed of a core of matter surrounded by subatomic particles that had unit electric charges . Beginning in 1846, German physicist Wilhelm Eduard Weber theorized that electricity was composed of positively and negatively charged fluids, and their interaction

3380-407: Is a challenging problem of modern theoretical physics. The admission of the hypothesis of a finite radius of the electron is incompatible to the premises of the theory of relativity. On the other hand, a point-like electron (zero radius) generates serious mathematical difficulties due to the self-energy of the electron tending to infinity. Observation of a single electron in a Penning trap suggests

3510-467: Is a combination of the words electr ic and i on . The suffix - on which is now used to designate other subatomic particles, such as a proton or neutron, is in turn derived from electron. While studying electrical conductivity in rarefied gases in 1859, the German physicist Julius Plücker observed the radiation emitted from the cathode caused phosphorescent light to appear on the tube wall near

3640-414: Is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z . The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have

3770-409: Is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature . Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition , which is when energy put into or taken out of the system goes into rearranging

3900-586: Is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics . A reaction is feasible only if the total change in the Gibbs free energy is negative, Δ G ≤ 0 {\displaystyle \Delta G\leq 0\,} ; if it is equal to zero the chemical reaction is said to be at equilibrium . There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by

4030-496: Is actually smaller than its true value, and the charge decreases with increasing distance from the electron. This polarization was confirmed experimentally in 1997 using the Japanese TRISTAN particle accelerator. Virtual particles cause a comparable shielding effect for the mass of the electron. The interaction with virtual particles also explains the small (about 0.1%) deviation of the intrinsic magnetic moment of

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4160-422: Is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology . Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. More than simple attraction and repulsion,

4290-439: Is also used to identify the composition of remote objects – like stars and distant galaxies – by analyzing their radiation spectra. The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. When a chemical substance is transformed as a result of its interaction with another substance or with energy,

4420-592: Is analogous to the rotation of the Earth on its axis as it orbits the Sun. The intrinsic angular momentum became known as spin , and explained the previously mysterious splitting of spectral lines observed with a high-resolution spectrograph ; this phenomenon is known as fine structure splitting. In his 1924 dissertation Recherches sur la théorie des quanta (Research on Quantum Theory), French physicist Louis de Broglie hypothesized that all matter can be represented as

4550-479: Is approximately 9.109 × 10  kg , or 5.489 × 10   Da . Due to mass–energy equivalence , this corresponds to a rest energy of 0.511 MeV (8.19 × 10  J) . The ratio between the mass of a proton and that of an electron is about 1836. Astronomical measurements show that the proton-to-electron mass ratio has held the same value, as is predicted by the Standard Model, for at least half

4680-464: Is called a mixture. Examples of mixtures are air and alloys . The mole is a unit of measurement that denotes an amount of substance (also called chemical amount). One mole is defined to contain exactly 6.022 140 76 × 10 particles ( atoms , molecules , ions , or electrons ), where the number of particles per mole is known as the Avogadro constant . Molar concentration is the amount of

4810-523: Is composed of gaseous matter that has been completely ionized, usually through high temperature. A substance can often be classified as an acid or a base . There are several different theories which explain acid–base behavior. The simplest is Arrhenius theory , which states that acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid–base theory , acids are substances that donate

4940-472: 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 number , and preferred types of bonds to form (e.g., metallic , ionic , covalent ). A chemical element

5070-464: Is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs . Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as

5200-455: Is in existence, the Coulomb force from the ambient electric field surrounding an electron causes a created positron to be attracted to the original electron, while a created electron experiences a repulsion. This causes what is called vacuum polarization . In effect, the vacuum behaves like a medium having a dielectric permittivity more than unity . Thus the effective charge of an electron

5330-537: Is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines . Different kinds of spectra are often used in chemical spectroscopy , e.g. IR , microwave , NMR , ESR , etc. Spectroscopy

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5460-570: Is one of humanity's earliest recorded experiences with electricity . In his 1600 treatise De Magnete , the English scientist William Gilbert coined the Neo-Latin term electrica , to refer to those substances with property similar to that of amber which attract small objects after being rubbed. Both electric and electricity are derived from the Latin ēlectrum (also the root of

5590-407: Is passed through parallel slits thereby creating interference patterns. In 1927, George Paget Thomson and Alexander Reid discovered the interference effect was produced when a beam of electrons was passed through thin celluloid foils and later metal films, and by American physicists Clinton Davisson and Lester Germer by the reflection of electrons from a crystal of nickel . Alexander Reid, who

5720-468: Is the crystal structure , or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water). Less familiar phases include plasmas , Bose–Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it

5850-458: Is the quantum mechanical model . Traditional chemistry starts with the study of elementary particles , atoms , molecules , substances , metals , crystals and other aggregates of matter . Matter can be studied in solid, liquid, gas and plasma states , in isolation or in combination. The interactions, reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of

5980-507: Is the probability of a molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation . The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound . A related concept free energy , which also incorporates entropy considerations,

6110-526: Is useful in identifying periodic trends . A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements. The standard nomenclature of compounds is set by the International Union of Pure and Applied Chemistry (IUPAC). Organic compounds are named according to the organic nomenclature system. The names for inorganic compounds are created according to

6240-461: The Dirac sea . This led him to predict the existence of a positron, the antimatter counterpart of the electron. This particle was discovered in 1932 by Carl Anderson , who proposed calling standard electrons negatrons and using electron as a generic term to describe both the positively and negatively charged variants. In 1947, Willis Lamb , working in collaboration with graduate student Robert Retherford , found that certain quantum states of

6370-458: The Lamb shift observed in spectral lines . The Compton Wavelength shows that near elementary particles such as the electron, the uncertainty of the energy allows for the creation of virtual particles near the electron. This wavelength explains the "static" of virtual particles around elementary particles at a close distance. An electron generates an electric field that exerts an attractive force on

6500-476: The Standard Model of particle physics. Individual electrons can now be easily confined in ultra small ( L = 20 nm , W = 20 nm ) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4  K ) to about −258 °C (15  K ). The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in

6630-509: The Woodward–Hoffmann rules often come in handy while proposing a mechanism for a chemical reaction. According to the IUPAC gold book, a chemical reaction is "a process that results in the interconversion of chemical species." Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction . An additional caveat is made, in that this definition includes cases where

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6760-416: The absolute value of this function is squared , it gives the probability that a particle will be observed near a location—a probability density . Electrons are identical particles because they cannot be distinguished from each other by their intrinsic physical properties. In quantum mechanics, this means that a pair of interacting electrons must be able to swap positions without an observable change to

6890-414: The age of the universe . Electrons have an electric charge of −1.602 176 634 × 10 coulombs , which is used as a standard unit of charge for subatomic particles, and is also called the elementary charge . Within the limits of experimental accuracy, the electron charge is identical to the charge of a proton, but with the opposite sign. The electron is commonly symbolized by e , and

7020-726: The alloy of the same name ), which came from the Greek word for amber, ἤλεκτρον ( ēlektron ). In the early 1700s, French chemist Charles François du Fay found that if a charged gold-leaf is repulsed by glass rubbed with silk, then the same charged gold-leaf is attracted by amber rubbed with wool. From this and other results of similar types of experiments, du Fay concluded that electricity consists of two electrical fluids , vitreous fluid from glass rubbed with silk and resinous fluid from amber rubbed with wool. These two fluids can neutralize each other when combined. American scientist Ebenezer Kinnersley later also independently reached

7150-455: The chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory . The chemistry laboratory stereotypically uses various forms of laboratory glassware . However glassware is not central to chemistry, and a great deal of experimental (as well as applied/industrial) chemistry is done without it. A chemical reaction is a transformation of some substances into one or more different substances. The basis of such

7280-493: The chemical industry . The word chemistry comes from a modification during the Renaissance of the word alchemy , which referred to an earlier set of practices that encompassed elements of chemistry, metallurgy , philosophy , astrology , astronomy , mysticism , and medicine . Alchemy is often associated with the quest to turn lead or other base metals into gold, though alchemists were also interested in many of

7410-405: The double-slit experiment . The wave-like nature of the electron allows it to pass through two parallel slits simultaneously, rather than just one slit as would be the case for a classical particle. In quantum mechanics, the wave-like property of one particle can be described mathematically as a complex -valued function, the wave function , commonly denoted by the Greek letter psi ( ψ ). When

7540-469: The duet rule , and in this way they are reaching the electron configuration of the noble gas helium , which has two electrons in its outer shell. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals. In

7670-462: The e / m ratio but did not take the step of interpreting their results as showing a new particle, while J. J. Thomson would subsequently in 1899 give estimates for the electron charge and mass as well: e  ~  6.8 × 10   esu and m  ~  3 × 10  g The name "electron" was adopted for these particles by the scientific community, mainly due to the advocation by G. F. FitzGerald , J. Larmor , and H. A. Lorentz . The term

7800-510: The inorganic nomenclature system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components. In addition the Chemical Abstracts Service has devised a method to index chemical substances. In this scheme each chemical substance is identifiable by a number known as its CAS registry number . A molecule is the smallest indivisible portion of

7930-500: The interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events'). An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons,

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8060-529: The intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H 2 O); a liquid at room temperature because its molecules are bound by hydrogen bonds . Whereas hydrogen sulfide (H 2 S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole–dipole interactions . The transfer of energy from one chemical substance to another depends on

8190-414: The muon and the tau , which are identical to the electron in charge, spin and interactions , but are more massive. Leptons differ from the other basic constituent of matter, the quarks , by their lack of strong interaction . All members of the lepton group are fermions because they all have half-odd integer spin; the electron has spin ⁠ 1 / 2 ⁠ . The invariant mass of an electron

8320-438: The size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat

8450-459: The spectral lines of the hydrogen atom. However, Bohr's model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atoms. Chemical bonds between atoms were explained by Gilbert Newton Lewis , who in 1916 proposed that a covalent bond between two atoms is maintained by a pair of electrons shared between them. Later, in 1927, Walter Heitler and Fritz London gave

8580-399: The spinon , the orbiton and the holon (or chargon). The electron can always be theoretically considered as a bound state of the three, with the spinon carrying the spin of the electron, the orbiton carrying the orbital degree of freedom and the chargon carrying the charge, but in certain conditions they can behave as independent quasiparticles . The issue of the radius of the electron

8710-599: The 1870s, the English chemist and physicist Sir William Crookes developed the first cathode-ray tube to have a high vacuum inside. He then showed in 1874 that the cathode rays can turn a small paddle wheel when placed in their path. Therefore, he concluded that the rays carried momentum. Furthermore, by applying a magnetic field, he was able to deflect the rays, thereby demonstrating that the beam behaved as though it were negatively charged. In 1879, he proposed that these properties could be explained by regarding cathode rays as composed of negatively charged gaseous molecules in

8840-477: The Coulomb force. Energy emission can occur when a moving electron is deflected by a charged particle, such as a proton. The deceleration of the electron results in the emission of Bremsstrahlung radiation. An inelastic collision between a photon (light) and a solitary (free) electron is called Compton scattering . This collision results in a transfer of momentum and energy between the particles, which modifies

8970-515: The Valence Shell Electron Pair Repulsion model ( VSEPR ), and the concept of oxidation number can be used to explain molecular structure and composition. An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and

9100-420: The atmosphere. The antiparticle of the electron is called the positron ; it is identical to the electron, except that it carries electrical charge of the opposite sign. When an electron collides with a positron , both particles can be annihilated , producing gamma ray photons . The ancient Greeks noticed that amber attracted small objects when rubbed with fur. Along with lightning , this phenomenon

9230-494: The atom is a positively charged ion or cation . When an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion . Cations and anions can form a crystalline lattice of neutral salts , such as the Na and Cl ions forming sodium chloride , or NaCl. Examples of polyatomic ions that do not split up during acid–base reactions are hydroxide (OH ) and phosphate (PO 4 ). Plasma

9360-652: The beam energy provides a relativistic Lorentz boost to the B meson particles produced in the collision. The direction of the higher-energy beam determines the 'forward' direction, and that affects the design of much of the Belle II detector . As with KEKB , SuperKEKB consists of two storage rings: one for the high-energy electron beam (the High Energy Ring, HER) and one for the lower energy positron beam (the Low Energy Ring, LER). The accelerator has

9490-480: The beginning of the twentieth century, it was found that under certain conditions a fast-moving charged particle caused a condensation of supersaturated water vapor along its path. In 1911, Charles Wilson used this principle to devise his cloud chamber so he could photograph the tracks of charged particles, such as fast-moving electrons. By 1914, experiments by physicists Ernest Rutherford , Henry Moseley , James Franck and Gustav Hertz had largely established

9620-536: The cancelled SuperB experiment. In the nano-beam scheme at SuperKEKB, the beams are squeezed in the vertical direction and the crossing angle is increased, which reduces the area of the crossing. The luminosity is further increased by a factor of two, due to a higher beam current than KEKB. The focus and crossing angle is achieved by two new superconducting quadrupole magnets at the interaction point that were installed in February 2017. On June 15, 2020, SuperKEKB set

9750-402: The cathode; and the region of the phosphorescent light could be moved by application of a magnetic field. In 1869, Plücker's student Johann Wilhelm Hittorf found that a solid body placed in between the cathode and the phosphorescence would cast a shadow upon the phosphorescent region of the tube. Hittorf inferred that there are straight rays emitted from the cathode and that the phosphorescence

9880-411: The changes they undergo during reactions with other substances . Chemistry also addresses the nature of chemical bonds in chemical compounds . In the scope of its subject, chemistry occupies an intermediate position between physics and biology . It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at

10010-553: The charge carriers were much heavier hydrogen or nitrogen atoms. Schuster's estimates would subsequently turn out to be largely correct. In 1892 Hendrik Lorentz suggested that the mass of these particles (electrons) could be a consequence of their electric charge. While studying naturally fluorescing minerals in 1896, the French physicist Henri Becquerel discovered that they emitted radiation without any exposure to an external energy source. These radioactive materials became

10140-588: The concept of an indivisible quantity of electric charge to explain the chemical properties of atoms. Irish physicist George Johnstone Stoney named this charge "electron" in 1891, and J. J. Thomson and his team of British physicists identified it as a particle in 1897 during the cathode-ray tube experiment . Electrons participate in nuclear reactions , such as nucleosynthesis in stars , where they are known as beta particles . Electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance, when cosmic rays enter

10270-412: The context of chemistry, energy is an attribute of a substance as a consequence of its atomic , molecular or aggregate structure . Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of

10400-430: The deflecting electrodes in a highly-conductive area of the tube, resulting in a strong screening effect close to their surface. The German-born British physicist Arthur Schuster expanded upon Crookes's experiments by placing metal plates parallel to the cathode rays and applying an electric potential between the plates. The field deflected the rays toward the positively charged plate, providing further evidence that

10530-427: The effects of quantum mechanics ; in reality, the so-called classical electron radius has little to do with the true fundamental structure of the electron. There are elementary particles that spontaneously decay into less massive particles. An example is the muon , with a mean lifetime of 2.2 × 10  seconds, which decays into an electron, a muon neutrino and an electron antineutrino . The electron, on

10660-454: The electron from the Bohr magneton (the anomalous magnetic moment ). The extraordinarily precise agreement of this predicted difference with the experimentally determined value is viewed as one of the great achievements of quantum electrodynamics . The apparent paradox in classical physics of a point particle electron having intrinsic angular momentum and magnetic moment can be explained by

10790-560: The electron has an intrinsic magnetic moment along its spin axis. It is approximately equal to one Bohr magneton , which is a physical constant that is equal to 9.274 010 0657 (29) × 10  J⋅T . The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity . The electron has no known substructure . Nevertheless, in condensed matter physics , spin–charge separation can occur in some materials. In such cases, electrons 'split' into three independent particles,

10920-429: The energies and distributions characterize the availability of an electron to bond to another atom. The chemical bond can be a covalent bond , an ionic bond , a hydrogen bond or just because of Van der Waals force . Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals . In many simple compounds, valence bond theory ,

11050-456: The energy states of an electron in a hydrogen atom that were equivalent to those that had been derived first by Bohr in 1913, and that were known to reproduce the hydrogen spectrum. Once spin and the interaction between multiple electrons were describable, quantum mechanics made it possible to predict the configuration of electrons in atoms with atomic numbers greater than hydrogen. In 1928, building on Wolfgang Pauli's work, Paul Dirac produced

11180-448: The first high-energy particle collider was ADONE , which began operations in 1968. This device accelerated electrons and positrons in opposite directions, effectively doubling the energy of their collision when compared to striking a static target with an electron. The Large Electron–Positron Collider (LEP) at CERN , which was operational from 1989 to 2000, achieved collision energies of 209 GeV and made important measurements for

11310-406: The formation of virtual photons in the electric field generated by the electron. These photons can heuristically be thought of as causing the electron to shift about in a jittery fashion (known as zitterbewegung ), which results in a net circular motion with precession . This motion produces both the spin and the magnetic moment of the electron. In atoms, this creation of virtual photons explains

11440-444: The formation or dissociation of molecules, that is, molecules breaking apart to form two or more molecules or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction , dissociation , acid–base neutralization and molecular rearrangement are some examples of common chemical reactions. A chemical reaction can be symbolically depicted through

11570-568: The full explanation of the electron-pair formation and chemical bonding in terms of quantum mechanics . In 1919, the American chemist Irving Langmuir elaborated on the Lewis's static model of the atom and suggested that all electrons were distributed in successive "concentric (nearly) spherical shells, all of equal thickness". In turn, he divided the shells into a number of cells each of which contained one pair of electrons. With this model Langmuir

11700-421: The hydrogen atom, which should have the same energy, were shifted in relation to each other; the difference came to be called the Lamb shift . About the same time, Polykarp Kusch , working with Henry M. Foley , discovered the magnetic moment of the electron is slightly larger than predicted by Dirac's theory. This small difference was later called anomalous magnetic dipole moment of the electron. This difference

11830-445: The ionic bond is the electrostatic force of attraction between them. For example, sodium (Na), a metal, loses one electron to become an Na cation while chlorine (Cl), a non-metal, gains this electron to become Cl . The ions are held together due to electrostatic attraction, and that compound sodium chloride (NaCl), or common table salt, is formed. In a covalent bond, one or more pairs of valence electrons are shared by two atoms:

11960-421: The light and free electrons is called Thomson scattering or linear Thomson scattering. Chemistry Chemistry is the scientific study of the properties and behavior of matter . It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms , molecules and ions : their composition, structure, properties, behavior and

12090-489: The magnetic field and the electron velocity. This centripetal force causes the electron to follow a helical trajectory through the field at a radius called the gyroradius . The acceleration from this curving motion induces the electron to radiate energy in the form of synchrotron radiation. The energy emission in turn causes a recoil of the electron, known as the Abraham–Lorentz–Dirac Force , which creates

12220-516: The magnetic field that drives an electric motor . The electromagnetic field of an arbitrary moving charged particle is expressed by the Liénard–Wiechert potentials , which are valid even when the particle's speed is close to that of light ( relativistic ). When an electron is moving through a magnetic field, it is subject to the Lorentz force that acts perpendicularly to the plane defined by

12350-473: The main characteristics of a molecule is its geometry often called its structure . While the structure of diatomic, triatomic or tetra-atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature. A chemical substance is a kind of matter with a definite composition and set of properties . A collection of substances

12480-426: The negatively charged particles produced by radioactive materials, by heated materials and by illuminated materials were universal. Thomson measured m / e for cathode ray "corpuscles", and made good estimates of the charge e , leading to value for the mass m , finding a value 1400 times less massive than the least massive ion known: hydrogen. In the same year Emil Wiechert and Walter Kaufmann also calculated

12610-1001: The observer will observe it to generate a magnetic field . Electromagnetic fields produced from other sources will affect the motion of an electron according to the Lorentz force law . Electrons radiate or absorb energy in the form of photons when they are accelerated. Laboratory instruments are capable of trapping individual electrons as well as electron plasma by the use of electromagnetic fields. Special telescopes can detect electron plasma in outer space. Electrons are involved in many applications, such as tribology or frictional charging, electrolysis, electrochemistry, battery technologies, electronics , welding , cathode-ray tubes , photoelectricity, photovoltaic solar panels, electron microscopes , radiation therapy , lasers , gaseous ionization detectors , and particle accelerators . Interactions involving electrons with other subatomic particles are of interest in fields such as chemistry and nuclear physics . The Coulomb force interaction between

12740-430: The other hand, is thought to be stable on theoretical grounds: the electron is the least massive particle with non-zero electric charge, so its decay would violate charge conservation . The experimental lower bound for the electron's mean lifetime is 6.6 × 10 years, at a 90% confidence level . As with all particles, electrons can act as waves. This is called the wave–particle duality and can be demonstrated using

12870-419: The other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals . However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up

13000-551: The photon, have symmetric wave functions instead. In the case of antisymmetry, solutions of the wave equation for interacting electrons result in a zero probability that each pair will occupy the same location or state. This is responsible for the Pauli exclusion principle , which precludes any two electrons from occupying the same quantum state. This principle explains many of the properties of electrons. For example, it causes groups of bound electrons to occupy different orbitals in an atom, rather than all overlapping each other in

13130-456: The positive protons within atomic nuclei and the negative electrons without allows the composition of the two known as atoms . Ionization or differences in the proportions of negative electrons versus positive nuclei changes the binding energy of an atomic system. The exchange or sharing of the electrons between two or more atoms is the main cause of chemical bonding . In 1838, British natural philosopher Richard Laming first hypothesized

13260-452: The positron is symbolized by e . The electron has an intrinsic angular momentum or spin of ⁠ ħ / 2 ⁠ . This property is usually stated by referring to the electron as a spin-1/2 particle. For such particles the spin magnitude is ⁠ ħ / 2 ⁠ , while the result of the measurement of a projection of the spin on any axis can only be ± ⁠ ħ / 2 ⁠ . In addition to spin,

13390-631: The questions of modern chemistry. The modern word alchemy in turn is derived from the Arabic word al-kīmīā ( الكیمیاء ). This may have Egyptian origins since al-kīmīā is derived from the Ancient Greek χημία , which is in turn derived from the word Kemet , which is the ancient name of Egypt in the Egyptian language. Alternately, al-kīmīā may derive from χημεία 'cast together'. The current model of atomic structure

13520-403: The rays carried negative charge. By measuring the amount of deflection for a given electric and magnetic field , in 1890 Schuster was able to estimate the charge-to-mass ratio of the ray components. However, this produced a value that was more than a thousand times greater than what was expected, so little credence was given to his calculations at the time. This is because it was assumed that

13650-478: The reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy . The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor e − E / k T {\displaystyle e^{-E/kT}} – that

13780-433: The reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions ,

13910-544: The resulting electrically neutral group of bonded atoms is termed a molecule . Atoms will share valence electrons in such a way as to create a noble gas electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule . However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow

14040-403: The rules of quantum mechanics , which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions. The phase of a substance is invariably determined by its energy and the energy of its surroundings. When

14170-455: The same conclusion. A decade later Benjamin Franklin proposed that electricity was not from different types of electrical fluid, but a single electrical fluid showing an excess (+) or deficit (−). He gave them the modern charge nomenclature of positive and negative respectively. Franklin thought of the charge carrier as being positive, but he did not correctly identify which situation was

14300-474: The same mass number; atoms of an element which have different mass numbers are known as isotopes . For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon , but atoms of carbon may have mass numbers of 12 or 13. The standard presentation of the chemical elements is in the periodic table , which orders elements by atomic number. The periodic table is arranged in groups , or columns, and periods , or rows. The periodic table

14430-423: The same orbit. In a simplified picture, which often tends to give the wrong idea but may serve to illustrate some aspects, every photon spends some time as a combination of a virtual electron plus its antiparticle, the virtual positron, which rapidly annihilate each other shortly thereafter. The combination of the energy variation needed to create these particles, and the time during which they exist, fall under

14560-489: The single particle formalism, by replacing its mass with the effective mass tensor . In the Standard Model of particle physics, electrons belong to the group of subatomic particles called leptons , which are believed to be fundamental or elementary particles . Electrons have the lowest mass of any charged lepton (or electrically charged particle of any type) and belong to the first generation of fundamental particles. The second and third generation contain charged leptons,

14690-593: The solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids , are organized in such a way as to lack the existence of identifiable molecules per se . Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt ), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. One of

14820-435: The state of the system. The wave function of fermions, including electrons, is antisymmetric, meaning that it changes sign when two electrons are swapped; that is, ψ ( r 1 , r 2 ) = − ψ ( r 2 , r 1 ) , where the variables r 1 and r 2 correspond to the first and second electrons, respectively. Since the absolute value is not changed by a sign swap, this corresponds to equal probabilities. Bosons , such as

14950-484: The structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons. In 1913, Danish physicist Niels Bohr postulated that electrons resided in quantized energy states, with their energies determined by the angular momentum of the electron's orbit about the nucleus. The electrons could move between those states, or orbits, by the emission or absorption of photons of specific frequencies. By means of these quantized orbits, he accurately explained

15080-695: The structure of the system, instead of changing the bulk conditions. Sometimes the distinction between phases can be continuous instead of having a discrete boundary' in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids , liquids , and gases . Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases

15210-421: The study of chemistry; some of them are: In chemistry, matter is defined as anything that has rest mass and volume (it takes up space) and is made up of particles . The particles that make up matter have rest mass as well – not all particles have rest mass, such as the photon . Matter can be a pure chemical substance or a mixture of substances. The atom is the basic unit of chemistry. It consists of

15340-504: The subject of much interest by scientists, including the New Zealand physicist Ernest Rutherford who discovered they emitted particles. He designated these particles alpha and beta , on the basis of their ability to penetrate matter. In 1900, Becquerel showed that the beta rays emitted by radium could be deflected by an electric field, and that their mass-to-charge ratio was the same as for cathode rays. This evidence strengthened

15470-423: The term electrolion in 1881. Ten years later, he switched to electron to describe these elementary charges, writing in 1894: "... an estimate was made of the actual amount of this most remarkable fundamental unit of electricity, for which I have since ventured to suggest the name electron ". A 1906 proposal to change to electrion failed because Hendrik Lorentz preferred to keep electron . The word electron

15600-522: The threshold of detectability expressed by the Heisenberg uncertainty relation , Δ E  · Δ t  ≥  ħ . In effect, the energy needed to create these virtual particles, Δ E , can be "borrowed" from the vacuum for a period of time, Δ t , so that their product is no more than the reduced Planck constant , ħ ≈ 6.6 × 10  eV·s . Thus, for a virtual electron, Δ t is at most 1.3 × 10  s . While an electron–positron virtual pair

15730-426: The upper limit of the particle's radius to be 10  meters. The upper bound of the electron radius of 10  meters can be derived using the uncertainty relation in energy. There is also a physical constant called the " classical electron radius ", with the much larger value of 2.8179 × 10  m , greater than the radius of the proton. However, the terminology comes from a simplistic calculation that ignores

15860-487: The view that electrons existed as components of atoms. In 1897, the British physicist J. J. Thomson , with his colleagues John S. Townsend and H. A. Wilson , performed experiments indicating that cathode rays really were unique particles, rather than waves, atoms or molecules as was believed earlier. By 1899 he showed that their charge-to-mass ratio, e / m , was independent of cathode material. He further showed that

15990-473: The wavelength of the photon by an amount called the Compton shift . The maximum magnitude of this wavelength shift is h / m e c , which is known as the Compton wavelength . For an electron, it has a value of 2.43 × 10  m . When the wavelength of the light is long (for instance, the wavelength of the visible light is 0.4–0.7 μm) the wavelength shift becomes negligible. Such interaction between

16120-563: Was Thomson's graduate student, performed the first experiments but he died soon after in a motorcycle accident and is rarely mentioned. De Broglie's prediction of a wave nature for electrons led Erwin Schrödinger to postulate a wave equation for electrons moving under the influence of the nucleus in the atom. In 1926, this equation, the Schrödinger equation , successfully described how electron waves propagated. Rather than yielding

16250-416: Was able to qualitatively explain the chemical properties of all elements in the periodic table, which were known to largely repeat themselves according to the periodic law . In 1924, Austrian physicist Wolfgang Pauli observed that the shell-like structure of the atom could be explained by a set of four parameters that defined every quantum energy state, as long as each state was occupied by no more than

16380-734: Was caused by the rays striking the tube walls. Furthermore, he also discovered that these rays are deflected by magnets just like lines of current. In 1876, the German physicist Eugen Goldstein showed that the rays were emitted perpendicular to the cathode surface, which distinguished between the rays that were emitted from the cathode and the incandescent light. Goldstein dubbed the rays cathode rays . Decades of experimental and theoretical research involving cathode rays were important in J. J. Thomson 's eventual discovery of electrons. Goldstein also experimented with double cathodes and hypothesized that one ray may repulse another, although he didn't believe that any particles might be involved. During

16510-672: Was governed by the inverse square law . After studying the phenomenon of electrolysis in 1874, Irish physicist George Johnstone Stoney suggested that there existed a "single definite quantity of electricity", the charge of a monovalent ion . He was able to estimate the value of this elementary charge e by means of Faraday's laws of electrolysis . However, Stoney believed these charges were permanently attached to atoms and could not be removed. In 1881, German physicist Hermann von Helmholtz argued that both positive and negative charges were divided into elementary parts, each of which "behaves like atoms of electricity". Stoney initially coined

16640-426: Was later explained by the theory of quantum electrodynamics , developed by Sin-Itiro Tomonaga , Julian Schwinger and Richard Feynman in the late 1940s. With the development of the particle accelerator during the first half of the twentieth century, physicists began to delve deeper into the properties of subatomic particles . The first successful attempt to accelerate electrons using electromagnetic induction

16770-415: Was made in 1942 by Donald Kerst . His initial betatron reached energies of 2.3 MeV, while subsequent betatrons achieved 300 MeV. In 1947, synchrotron radiation was discovered with a 70 MeV electron synchrotron at General Electric . This radiation was caused by the acceleration of electrons through a magnetic field as they moved near the speed of light. With a beam energy of 1.5 GeV,

16900-413: Was originally coined by George Johnstone Stoney in 1891 as a tentative name for the basic unit of electrical charge (which had then yet to be discovered). The electron's charge was more carefully measured by the American physicists Robert Millikan and Harvey Fletcher in their oil-drop experiment of 1909, the results of which were published in 1911. This experiment used an electric field to prevent

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