हिन्दी अंग्रेज़ी परिभाषा A*/E low-field absorption/high-field emission with net absorptive character ab initio from first principles abscissa the name given to the horizontal axis in a set of two-dimensional coordinates. Commonly referred to as the x-axis. परम ताप absolute temperature This is a temperature reading made relative to absolute zero. We use the unit of Kelvins for these readings. परम शून्य absolute zero This is the lowest temperature possible. If you remember that temperature is a measurement of how much atoms move around in a solid, you can guess that they stop moving entirely at absolute zero. In reality, bonds still vibrate a little bit, but for the most part you don't see much happening. absorption filter filter which allow all light through except for that in a narrow region; this is caused by the light being absorbed by the filter material. ac arc a method of vaporization and excitation in emission spectroscopy, using voltages of less than 5000 V. Results with this method are more reproducible than that possible with a dc arc. ac spark put a charge of 40,000V across two electrodes; the electrons which flow between them will ionize the sample. acceleration slits positively charged ions produced in an ionization chamber of a mass spectrometer are passed into the analyzer by the accleration slits. Generally, two acceleration slits are used; one has a slight negative potential with respect to the ionization chamber in order to attract the positive ions, and the other slit has an extremely high voltage which accelerates that ions to up to half the speed of light. शुद्धि accuracy When you measure something, the accuracy is how close your measured value is to the real value. For example, if you're actually six feet tall and your brother measures your height as six feet, one inch, he's pretty accurate. However, if your cousin measures your height as twelve feet, 13 inches, he's not accurate at all. ACF activated carbon fibers अम्ल acid This is anything that gives off H+ ions in water. Acids have a pH less than 7 and are good at dissolving metals. They turn litmus paper red and phenolphthalein colorless. acid anhydride This is an oxide that forms an acid when you stick it in water. An example is SO3 - when you add water it turns into sulfuric acid, H2SO4. acid dissociation constant (Ka) This is equal to the ratio of the concentrations of an acid's conjugate base and the acid present when a weak acid dissociates in water. That is, if you have a solution of Acid X where the concentration of the conjugate base is 0.5 M and the concentration of the acid is 10 M, the acid dissociation constant is 0.5/10 = 0.05. activated complex In a chemical reaction, the reagents have to join together into a great big blob before they can fall back apart into the products. This great big blob is called the activated complex (a.k.a. transition state) activation energy The minimum amount of energy needed for a chemical reaction to take place. For some reactions this is very small (it only takes a spark to make gasoline burn). For others, it's very high (when you burn magnesium, you need to hold it over a Bunsen burner for a minute or so). activity series This is when you arrange elements in the order of how much they tend to react with water and acids. actual yield When you do a chemical reaction, this is the amount of chemical that you actually make (i.e. The amount of stuff you can weigh). addition reaction A reaction where atoms add to a carbon-carbon multiple bond. adhesion the force between unlike molecules adsorption When one substance collects of the surface of another one. प्रश्लिष aerosols dispersions of liquids in gases and solids in gases. afocal system where both the object and image are focused at infinity. Primarily used in magnification, or when a beam needs to be expanded but not focused. AIMD ab inito molecular dynamics एल्कोहल alcohol An organic molecule containing an -OH group aldehyde An organic molecule containing a -COH group alkali metals Group I in the periodic table. alkaline earth metals Group II in the periodic table. alkane An organic molecule which contains only single carbon-carbon bonds. alkene An organic molecule containing at least one C=C bond alkyne An organic molecule containing at least one C-C triple bond. allomorph any of two or more crystalline forms of a substance allotropes When you have different forms of an element in the same state. The relationship that white phosphorus and red phosphorus have to each other is that they're allotropes. allotropic variation of physical properties without change in substance. Example: graphite, charcoal and diamond are allotropes of carbon. मिश्रधातु alloy A mixture of two metals. Usually, you add very small amounts of a different element to make the metal stronger and harder. ALON also known as Raytran, Al23O27N5, a glass used in IR spectroscopy अल्फा कण alpha particle A radioactive particle equivalent to a helium nucleus (2 protons, 2 neutrons) alpha particles the helium nucleus. alpha-AgI A form of silver iodide which is stable at high temperatures. It acts as a superionic material, conducting electricity effectively through ionic transport. Degrades below 147 C to beta-AgI. alpha-electron an electron in which the spin is +1/2 aluminosilicates silicates with aluminum occupying some of the silicon sites. a-MCMB’s Activated mesocarbon microbeads. Show ferromagnetism at low temperatures amine An organic molecule which consists of an ammonia molecule where one or more of the hydrogen atoms has been replaced by organic groups. amino acid The basic building blocks of proteins. They're called "amino acids" because they're both amines (they contain nitrogen) and acids (carboxylic acids, to be precise) ammeter a device that measures current amphiprotic When something is both an acid and a base. Like amino acids, for example. ampholyte a substance that may act as either an acid or a base amphoteric When something is both an acid and a base. Sounds familiar, huh? analyzer tube a part of a mass spectrometer in which positive ions are separated according to their mass/charge ratios. In TOF, this part is straight, in others, curved. angstrom 10–10 meters. anion photoelectron spectroscopy what you do is hit a sample with a laser and create anions. A carrier gas takes the anions down to a magnetic-bottle time-of-flight photoelectron analyzer, where you can characterize them. anisotropy when something is not isotropic; you look at how much something is not random, and the measure of this non-randomness is the anisotropy. annealing the tempering of glass or metals by heat. Can also be used as a treatment for thin films to give them the desired properties. annealing point the temperature at which residual strain or stress in a glass will relieve itself in a few minutes. annulene totally conjugated hydrocarbon धनाग्र anode The electrode where oxidation occurs. In other words, this is where electrons are lost by a substance. anode the electrode where oxidation occurs antiferromagnetism where there is no net magnetic moment because the spin magnetic moments are randomly oriented, canceling them. antinodes points of constructive interference between two waves antireflection coating increases energy transmitted through optical surfaces by reducing Fresnel reflection losses. The criteria for such a coating are that the refractive index of the material must be equal to the square root of the substrate index when the substrate is in air; also, the phase difference between the incident wave and reflected wave must be an odd multiple of pi. anti-Stokes fluorescence although most fluorescence complies with the Stokes law, a weak fluorescence is found at a shorter wavelength than the exciting wavelength. This additional energy is gained from excited vibrational levels within the ground state. appearance potential the potential required to get fragmentation ions in a mass spectrometer. Generally, this value is 1-4 eV greater than the value for the ionization energy of the corresponding molecular ion. जलीय aqueous dissolved in water AR antireflective coating Archimedes principle the buoyant force on a body immersed in a fluid is equal to the weight of the fluid displaced by that object. armature where the coils of wire are mounted on an electric motor arsenic trisulfide material used in IR windows (0.6-11 microns) Arsenous acid H3AsO3 ASED atom superposition and electron delocalization: a method used in extended-Huckel calculations. asphaltanes heavy polyaromatics which are insoluble in n-hydrocarbon solvents, produced in oil refineries from the vacuum distillation of virgin crude oils and processed petroleum. They form unit sheets which are arranged in stacks; the number of unit sheets which join together and the height of these sheets is strongly solvent dependant. astigmatism when the lens is focused in one plane, but not in the plane 90 degrees to it. atmosphere 760 torr, 101.325 kPa atomic absorption spectroscopy (AAS) ionize a sample, and then hit the ions with light and see where absorptions take place. atomic emission spectroscopy (AES) heat a sample and it ionizes; measure the wavelengths of the relaxations of these ions. atomic fluorescence spectroscopy (AFS) same as AAS, but you measure the wavelengths that pass through without being absorbed. परमाणु द्रब्यमान इकाई atomic mass unit (a.m.u.) This is the smallest unit of mass we use in chemistry, and is equivalent to 1/12 the mass of carbon-12. To all intents and purposes, protons and neutrons weigh 1 a.m.u. परमाणू त्रिज्या atomic radius This is one half the distance between two bonded nuclei. Why don't we just measure the distance from the nucleus to the outside of the atom - after all, isn't that the same thing as a radius? It is, but atoms are also (theoretically) infinitely large (due to quantum mechanics), making this impossible to measure. atomic solid A solid where there's a bunch of atoms in the lattice. This is different from an ionic solid, where ions are the things that are sticking together. attenuator used in e.s.r, the attenuation of the microwave power passing along a waveguide is achieved by means of a metal plate placed along the axis of the waveguide. The degree of attenuation increases as the plate is moved away from the wall of the waveguide toward the center. In IR and UV spectroscopy, the attenuator is a toothed comb, grid, or star arrangement introduced into one beam of a spectrometer, operated either automatically through an electronic servosystem, or manually to balance the radiation in both beams. Auer burner one source of radiation for far-IR spectroscopy. Consists of a thorium oxide mantle heated to ~2000K by a burning gas. Optimum wavelength is ~50 microns. आफबाउ का सिद्धान्त Aufbau principle When you add protons to the nucleus to build up the elements, electrons are added into orbitals. Auger effect the emission of a second electron after high energy radiation has expelled another. Auger electron spectroscopy The use of the Auger effect to determine orbital energies and structure of the molecule. autoprotolysis solvent dissociation into anion and proton. auxochrome a saturated group with nonbonded electrons which, when attached to a chromophore, alters both the wavelength and intensity of an absorption. अवगाद्रो का नियम Avogadro's Law If you've got two gases under the same conditions of temperature, pressure, and volume, they've got the same number of particles (atoms or molecules). This law only works for ideal gases, none of which actually exist. azeotrope some composition of a binary mix in which the two portions cannot be separated by distillation. b A computer program that allows people to generate accurate structures for biomolecules background region the region of low transmission of a pass filter. bar 100 kPa barrier-layer cell a photoelectric detector which is made of iron coated with a semiconductor film; when light from 250-750 nm hits this cell, you get a current; this is a cell which is mainly good for intense light sources, because there is not a huge signal enhancement. क्षार base A compound that gives off OH- ions in water. They are slippery and bitter and have a pH greater than 7. base anhydride An oxide that forms a base when water is added. CaO is an example, turning into calcium hydroxide in water. basis set truncation error the error you get in computational methods from not expanding an infinite series all the way to infinity. the more terms you use, the less basis set truncation error you get. bathochromic shift shift of an absorption to a longer wavelength due to substitution or solvent effect (red shift). बैटरी battery This is when a bunch of voltaic cells are stuck together. Bayer process used to obtain aluminum from bauxite BEEQ mass spectrometer a type of mass spectrometer, where the B stands for the magnetic sector, E stands for the electric sector, and Q stands for the quadropole mass filter. All of these letters stand for devices which can be used to separate the ionic products into the desired types. bequerel SI unit of radioactivity, equal to one disintegration per second. Bernoulli’s principle where the velocity of a fluid is high, the pressure is low, and vice-versa beta electron an electron in which the spin is -1/2 बीटा कण beta particle A radioactive particle equivalent to an electron. beta particle electron bidentate ligand A ligand that can attach twice to a metal ion. bifurcation division into two parts or branches or where these branches split apart binary compound A compound only having two elements बंधन उर्जा binding energy The amount of energy that holds the neutrons and protons together in the nucleus of an atom. It's a lot of energy, which is why you don't see nuclei falling apart all over the place. BIOGRAF a computer program that allows the user to determine the positions of atoms or ions in biological molecules. birefringence when a single incident beam is split into two refracted beams. Both of the refracted beams are parallel, with one offset from the other. bistability when a system is able to exist in either of two steady states. blaze wavelength the wavelength or which the angle of reflection from the groove face of a grating and the diffraction angle are the same. BLM bilayer lipid membrane Bohr radius the radius of the n=1 orbital in hydrogen. .529exp(-10) m. bolometer an IR detector where changes in temperature of the responsive element due to incident radiation causes a change in conductivity of the element. बाण्ड उर्जा bond energy The amount of energy it takes to break one mole of bonds. बाण्ड लम्बाई bond length The average distance between the nuclei of two bonded atoms. bonded phase chromatography (BPC) where the stationary phase of the analyte actually bonds to a solid surface; the solid surface usually consists of silica-based particles. Born-Oppenheimer approximation nuclei are so heavy that they stay essentially stationary during the timescale of electron transfer processes Boudouard carbon A form of carbon which is generated catalytically in the gas phase. बायल का नियम Boyle's Law The volume of a gas at constant temperature varies inversely with pressure. In other words, if you put big pressure on something, it gets small. Bragg equation relates the angles at which X-rays are scattered from a crystal to the spacing between the layers of molecules. Brewster angle used in laser rod windows, at this angle light polarized in one direction passes through with very little reflection. Can be used to control the polarization of light leaving a laser. Can be calculated using tan(thetaBrewster)=n of the refractive material (where n is the refractive index). ब्रान्स्टेट-लौरी अम्ल Bronsted-Lowry acid Acids donate protons [H+ ions] and bases grab them Brusselators cells a theoretical system of oscillatory cells; useful because they can accurately model biological systems. बफर buffer A liquid that resists change in pH by the addition of acid or base. It consists of a weak acid and it's conjugate base (acetic acid and sodium acetate, for example). bulk modulus (K) defined as the ratio of hydrostatic pressure to fractional decrease in volume. calcite calcium carbonate उष्मामापन calorimetry The study of heat flow. Usually you'd do calorimetry to find the heat of combustion of a compound or the heat of reaction of two compounds. capacitor a device for storing electric charge; consists of two conducting objects placed near each other but not touching; typically, when there is a voltage gradient between them, the energy can be kept stored until it needs to be discharged or until the voltage grows high enough that it spontaneously discharges. carbon arc a carbon electrode superheated so that it emits light. Good for producing IR radiation between 10-100 microns. carbon filament atom reservoir used in atomic spectroscopy, it enables materials to be examined without the use of highly flammable materials. When the sample is passed through a graphite tube under high voltage, it is atomized. carboxylic acid An organic molecule with a -COOH group on it. Acetic acid is the most famous one. carrier gas any gas used in a process which serves as a solvent for the chemical of interest. Useful in GC and other processes. cascade process the procedure for increasing the strength of a weak signal by the progressive build-up of electron displacement in a series of dynode plates in a photomultiplier. CASSCRF complete active space multiconfiguration self-consistent field; something that is incorporated into very complete ab initio molecular dynamics calculations. catadiotropic systems optical systems which contain both reflecting and refracting elements; handy for correcting aberrations over wide angular fields. उत्प्रेरक catalyst A substance that speeds up a chemical reaction without being used up by the reaction. Enzymes are catalysts because they allow the reactions that take place in the body to occur fast enough that we can live. catenation the linking of like atoms to form chains or rings. ऋणाग्र cathode The electrode in which reduction occurs. Reduction is when a compound gains electrons. cathode electrode where reduction occurs CBS complete basis set cellulose a polysaccharide of glucose; the main component of plants. centripetal force the force which always points from a body in rotation to the center of rotation CESR conduction electron spin resonance शृंखला अभिक्रिया chain reaction A reaction in which the products from one step provide the reagents for the next one. This is frequently referred to in nuclear fission (when large nuclei break apart to form smaller ones) and in free-radical reactions. channeltron a variant of the electron multiplier; used to enhance electron signals चार्ल का नियम Charles's Law The volume of a gas at constant pressure is directly proportional to the temperature. In other words, if you heat something up, it gets big. CHARMM a computatinal method for simulate protein dynamics in water. रासायनिक समीकरण chemical equation The recipe that describes what you need to do to make a reaction take place. chemical equivalence when a nucleus or group of nuclei are related by a symmetry operation of the molecule and have the same chemical shifts. chemical oxygen-iodine lasers (COIL) Lasers in which O2(a1deltag) generated chemically spurs the subsequent excitation of iodine atoms. Multi-kilowatt power possible. रासायनिक गुण chemical properties Properties that can only be described by making a chemical change (by making or breaking bonds). For example, color isn't a chemical property because you don't need to change something chemically to see what color it is. Flammability, on the other hand, is a chemical property, because you can't tell if something burns unless you actually try to burn it. chemical shift the difference in the absorption spectrum of a particular proton from the absorption position of a reference proton. chemical vapor deposition use a vapor transport mechanism in which the gaseous reactants decompose and recombine to form some desired thin film. Decomposition and reaction are helped by having a heated substrate. chirality When a molecule has a nonsuperimposable mirror image. To imagine this, put your hands together. Although they are mirror images, you can't put them right on top of each other so they are interchangable. Well, normal people can't, anyway. choke coil a coil that has significant self-inductance Christiansen filter used as a bandpass filter, these filters transmit light where the refractive index of the material matches that of the light. This wavelength changes with temperature, so when using one of these filters the temperature must be kept roughly constant. chromatic aberration when the different wavelengths of light passing through a lens focus at different points. This effect arises from the fact that different wavelengths of light experience different refractive indexes when passing through a material. chromatography This is when you use a system containing a mobile phase (usually a liquid in general chemistry classes) and a stationary phase (something dissolved in the liquid) to separate different compounds. This is usually done by exploiting the differing polarities of solutes, though you can do it a whole slew o' ways. chromophore functional groups with characteristic optical absorptions or the molecules which contain them CIDEP chemically induced dynamic electron polarization परिपथ circuit The closed path in a circuit through which electrons flow. circular dichroism (CD) optically active materials absorb left and right circularly polarized light to different extents. clathrate a water cage that forms around a hydrocarbon in solution. cloud chamber A device which is used to determine which elementary particles are being generated in a nuclear reaction. What happens is that the elementary particles go zipping through a saturated water fog, and the ionized water molecules provide nucleation centers for the condensation of water. From following these tracks, the identities of the particles can be determined. coagulation When you destroy a colloid by letting the particles settle out. coexistance curve a plot of density versus temperature for some substance. It measures the range over which the liquid and vapor phases can exist in equilibrium. coherence length how long it is before waves from a light source get out of step. The less wide the spread of radiation leaving the source, the longer the coherence length. coherent Raman beat (CRB) an ESR technique in which you monitor the electron resonance using a single, weak microwave field. The purpose is to detect coherences between nuclear transitions that are in hyperfine contact with the unpaired electron spin. cohesion the force between like molecules cold mirror reflects visible and transmits IR light colligative property Any property of a solution that changes when the concentration changes. Examples are color, flavor, boiling point, melting point, and osmotic pressure. collimated forming a highly non-divergent beam colloid It's a suspension. colloid when large numbers of molecules swarm together due to intermolecular forces. The dispersed phase in a colloid has a huge surface area coma the variation of focal length with aperture. combination bands describes weak absorptions in IR spectra corresponding to the sum of two or more fundamental vibrational frequencies. These combination modes arise from the anharmonicities of the oscillators which leads to an interaction of the vibrational states in polyatomic molecules. ज्वलन combustion When a compound combines with oxygen gas to form water, heat, and carbon dioxide समान आयन प्रभाव common ion effect When the equilibrium position of a process is altered by adding another compound containing one of the same ions that's in the equilibrium. complex conjugate the imaginary portion of some function f(x) complex ion An ion in which a central atom (usually a transition metal) is surrounded by a bunch of molecules like water or ammonia (called "ligands") compression factor (Z) one way of determining how a gas deviates from ideality; Z=1 for ideal gases. Compton effect the observation that X-rays scattered off of materials have a lower frequency than the incident X-rays. Attributed to collisions between the X-rays and electrons. सांद्रता concentration A measurement of the amount of stuff (solute) dissolved in a liquid (solvent). The most common concentration unit is molarity (M), which is equal to the number of moles of solute divided by the number of liters of solution. condensation When a vapor reforms a liquid. This is what happens on your bathroom mirror when you take a shower. चालकता conductance A measurement of how well electricity can flow through an object. conduction the result of collisions between molecules; when one end of an object is heated, the molecules vibrate faster and the energy is transferred to their neighbors. युग्मी अम्ल conjugate acid The compound formed when a base gains a proton (hydrogen atom). युग्मी क्षार conjugate base The compound formed when an acid loses a proton (hydrogen atom). Continuous flow stirred tank reactors (CSTR) Reactors in which reagents go in, are stirred, and products come out. May also be used for other purposes, such as coupling many reaction chambers to each other in a network. सतत स्पेक्ट्रम continuous spectrum A spectrum that gives off all the colors of light, like a rainbow. This is caused by blackbody emission. convection when heat is transferred by the mass movement of molecules from one place to another. copolymer when two or more monomeric units of different type are strung togther into a polymer. coprecipitation when some precipitate contains an impurity within its bulk. Coriolis force used in rotating body problems, it is a pseudoforce that explains why bodies at the outer edge of a rotating disk experience higher linear speeds. corner-cube prisms also called retroreflectors, they have one corner of a cube which collects the light and returns it to the original source. Corning 9753 calcium aluminosilicate; transmits from 0.3-4.6 microns cornu mounting a prism system employed in spectrophotometers in which radiation is passed in through one face of the prism and out through the opposite face. The prism employed for this purpose is formed from two thirty degree quartz prisms, one of right-handed quartz and one of left-handed quartz. Produces very good dispersion but no polarization. COSMOSIL SPYE a material used in HPLC columns. Good for separating fullerenes. COSY correlated spectroscopy; a two-D NMR technique. coulombic attraction the positive-negative attraction which takes place when you have two charged particles in close proximity coulometric titration a titration method in which the current passed through the sample is used to indicate completion of the reaction. coupling constant the separation between the peaks of a first-order multiplet produced as a result of spin-orbit coupling. The larger the value of J, the greater the coupling between the nuclei. J is usually measured in Hertz, and is not dependant on the operating frequency of the instrument. covalent bond A chemical bond formed when two atoms share two electrons. CPMAS NMR stands for charge polarized magic angle spinning nuclear magnetic resonance. Basically this is a method for taking molecules that have high degrees of spin and imparting some of that spin to molecules that have none. It’s handy for getting NMR signals off of atoms that usually do not have signals. क्रान्तिक द्रब्यमान critical mass The minimum amount of radioactive material needed to undergo a nuclear chain reaction. क्रान्तिक बिन्दु critical point The end point of the liquid-vapor line in a phase diagram. Past the critical point, you get something called a "supercritical liquid", which has weird properties. cross-product A cross B = [A][B]sin(theta) cryoscopic constant used to measure the freezing point depression with the addition of a solvent. क्रिस्टल crystal A large chunk of an ionic solid. crystal lattice see "lattice" curie 3.7 exp10 nuclear disintegrations/sec. Curie temperature where a ferromagnetic transition occurs CVD chemical vapor deposition cyclic voltammetry a method for determining the kinetics of electrode processes. Current is monitored as the potential of the electrode is changed. डाल्टन का आंशिक दाब का सिद्धान्त Dalton's law of partial pressures The total pressure in a mixture of gases is equal to the sums of the partial pressures of all the gases put together. damped harmonic motion when there is friction within an oscillating system, the amplitudes of the oscillation decrease over time due to this damping force. dark current the background current that flows in photoemissive and photoconductive detectors when no radiation is falling on the detector. It is a temperature-dependant effect, and can be decreased by many orders of magnitude by operating below -20C. dc arc put a voltage of 200-300 V across two graphite electrodes separated by about one centimeter; resulting heat causes ionization of the sample. This is commonly used in atomic absorption spectroscopy. Debye temperature the temperature above which a certain crystal behaves classically; the temperature above which thermal vibrations are more important than quantum effects decomposition When a big molecule falls apart to make two or more little ones. degeneracy when one energy level corresponds to two or more states of motion. It arises when the symmetry of a molecule is such that certain fundamental frequencies are equal and is a common feature in IR spectroscopy. degenerate Things (usually orbitals) are said to be degenerate if they have the same energy. This term is used a whole lot in quantum mechanics. Also when dealing with kids who steal cars. deintercalation the expulsion of a foreign atom from some crystal lattice where it has been residing (usually in interstitial spaces). The opposite of intercalation. delocalization This is when electrons can move around all over a molecule. This happens when you have double bonds on adjacent atoms in a molecule (conjugated hydrocarbon) denature When the 3-D structure of a protein breaks down due to heat (or pH, etc), it's said to be denatured. This means that it unravels because the intermolecular forces between atoms in the chain aren't strong enough to hold it together anymore. depolarization factor by enclosing the sample tube in polarizing sheets, each line in a Raman spectrum can be split into a horizontal component and a vertical component. The depolarization factor is the ratio of these two components. Devarda’s alloy 50% Cu, 45% Al, 5% Zn; used to reduce inorganic nitrates and nitrites to ammonia. dew point when air containing a given amount of water is cooled, the temperature at which the partial pressure of water equals the saturated vapor pressure. DFT density functional theory dialysis the separation of small solute particles from colloid particles by means of a semi-permeable membrane. diamagnetic a diamagnetic material has no unpaired spins; when such a material without permanent dipoles has a magnetic field applied to it, the magnetic dipoles induced in the material line up opposite to that of the induced field. diastereotopic non-interchangeable protons; the chemical shift is not ever equivalent diathermic something that allows energy transfer as heat विसरण diffusion When particles move from areas of high concentration to areas of low concentration. For example, if you open a bottle of ammonia on one end of the room, the concentration of ammonia molecules in the air is very high on that side of the room. As a result, they tend to migrate across the room, which explains why you can smell it after a little while. Be careful not to mix this up with effusion (see definition) dilute-spin species when you have a species that is not very abundant; there is very little chance that there will be more than one magnetically-active isotope in a molecule. तनुकरण dilution When you add solvent to a solution to make it less concentrated. द्विध्रुव आघूर्ण dipole moment When a molecule has some charge separation (usually because the molecule is polar), it's said to have a dipole moment. द्विध्रुव-द्विध्रुव बल dipole-dipole force When the positive end of a polar molecule becomes attracted to the negative end of another polar molecule. dispersion the spreading of white light into the full spectrum बिलयन dissociation When water dissolves a compound. आसवन distillation This is when you separate a mixture of liquids by heating it up. The one with the lowest boiling point evaporates first, followed by the one with the next lowest boiling point, etc. distortion departure of image shape from that predicted by first-order Gaussian optics; one example, when a rectangle is shaped like a pillow. Doppler effect the phenomena that the frequencies of waves are blue-shifted when the source moves toward the observer and red-shifted when the source moves away from the observer. dot product A dot B = AB cos (theta) double-displacement reaction (a.k.a. double replacement reaction) When the cations of two ionic compounds switch places. Dove prisms used to rotate the image in optical systems DQ duroquinone, also known as tetramethyl-1,4-benzoquinone drift region the length that the charged ions travel through in a TOF mass spec. ductility how much strain a material will take before it breaks. dynode the anodes which are used to amplify the signal in photomultiplier tubes. E/A* low field emission/high field absorption with net absorptive character ebullioscopic constant used to measure the boiling point elevation of a solvent with the addition of a solute effective nuclear charge the net positive charge experienced by an electron in a many-electron atom. effusion When a gas moves through an opening into a chamber that contains no pressure. Effusion is much faster than diffusion because there are no other gas molecules to get in the way. effusion the rate at which a gas escapes through an orifice or hole. EHMO extended Huckel molecular orbital einsel lens produces focusing without an overall change in the energy of the transmitted particle. A lens used in TOF mass spec devices. einstein the amount of energy absorbed by one mole of material undergoing a photochemical reaction elastic deformation the linear region on a strain versus stress plot where a material will still assume its original shape. विद्युत अपघटन electrolysis When electricity is used to break apart a chemical compound. विद्युत अपघट्य electrolyte An ionic compound that dissolves in water to conduct electricity. Strong electrolytes break apart completely in water; weak electrolytes only fall apart a little bit. (Actually, this isn't entirely true, as Raji Heyovska informs me. Apparently strong electrolytes also dissociate partially in water, though much more so than weak ones. For more info, check out his paper at http://www.jh-inst.cas.cz/~rheyrovs. However, it is also true that the usual definition of a strong electrolyte is one that dissociates completely in water, which is why I include that definition above.) electrolytic cell an electrochemical cell in which a non-spontaneous reaction is driven by an outside current electron affinity The energy change that accompanies the addition of an electron to an atom in the gas phase. electron affinity how much something wants to pick up electrons. A exothermic electron gain corresponds to a positive electron affinity. electron gun use a controlled beam of electrons striking a surface to elevate a local area to evaporation temperature; often used in manufacture of films by vapor deposition electron impact (EI) a commonly-used mode in a mass spec where molecules in the vapor phase are bombarded with a high-energy electron beam. These impacts are recorded as a spectrum of positive ions separated on the basis of mass/charge (m/z). electron magnetic resonance (EMR) covers a wide range of experimets including ESE, CRB, and others in the field of ESR. electron spin echo (ESE) a method in which you initially hit your sample, and follow that up with other pulses to generate these spin echoes. An ESR technique. electron spin echo envelope modulation (ESEEM) a method similar to CRB, except that you typically require three pulses instead of the one required by CRB. electron spin resonance (ESR) Also known as electron paramagnetic resonance (EPR), this method is used to determine whether radicals are formed in solution. Although it is very useful at this purpose, the sensitivity toward determination of structure is poor. It is the study of molecules containing unpaired electrons by observing the magnetic fields at which they come into resonance with monochromatic radiation. The radiation is in the microwave region, and the magnetic fields are about .3 Tesla. It can be used to study radicals generated either through chemical reactions or radiation, as well as d-metal complexes and molecules in triplet states. electron volt corresponds to the energy acquired by an electron accelerated through a potential difference of one volt. 1eV corresponds to 1.602exp(-19)J. electronegativity A measurement of how much an atom tends to steal electrons from atoms that it's bonded to. Elements at the top right of the periodic table (excluding the noble gases) are very electronegative while atoms in the bottom left are not very electronegative (a.k.a. "electropositive") electroosmosis The process by which charged particles will tend to migrate toward a less charged area. Generally, when we think of this, we think of an electrolysis process where cations move in one direction, anions move in the other, and the net movement over the sample is zero. However, commonly there are areas of higher charge density, and the electroosmotic effect can greatly affect the behavior of the liquid. electropositive When something is not at all electronegative. In fact, it tends to lose electrons rather than to gain them. Elements that are electropositive are generally to the left and bottom of the periodic table. electrostatics the study of charges at rest empirical formula A reduced molecular formula. If you have a molecular formula and you can reduce all of the subscripts by some constant number, the result is the empirical formula. emulsion When very small drops of a liquid are suspended in another. An example of an emulsion is salad dressing after you've shaken it up. emulsion dispersions of liquids in liquids, as in milk enantiomers molecules that are nonsuperimposable mirror images of each other. enantiotopic protons that are interchangeable through any symmetry operation (except rotation). The chemical shift is the same for these protons in an achiral environment. ENDOR electron nuclear double resonance; an ESR technique endothermic When a process absorbs energy (gets cold). endpoint The point where you actually stop a titration, usually because an indicator has changed color. This is different than the "equivalence point" because the indicator might not change colors at the exact instant that the solution is neutral. energy level A possible level of energy that an electron can have in an atom. enthalpy A measurement of the energy content of a system. entropy A measurement of the randomness in a system. enzyme A biological molecule that catalyzes reactions in living creatures. epitaxial the growth of one layer of crystals on another such that they have the same structure equilibrium When the forward rate of a chemical reaction is the same as the reverse rate. This only takes place in reversible reactions because these are the only type of reaction in which the forward and backward reactions can both take place. equivalence point The point in a titration at which the solution is completely neutral. This is different than the "endpoint" (see above). escape depth the maximum depth under a surface from which ionized electrons come ester An organic molecule with R-CO-OR' functionality. eutectic temperature the temperature in a 2-component mixture where a liquid solution and both pure solids exist at a fixed pressure. evanescent wave a wave on the other side of a surface from a total internal reflection; decays exponentially with distance. even function a function in which f(x)=f(-x) EXAFS extended X-ray absorption fine structure excess reagent Sometimes when you do a chemical reaction, there's some of one reagent left over. That's called the excess reagent. excimer a combination of two atoms which survives only in an excited state and which dissolves as soon as the excitation has been lost Excimer laser A laser which is used to pump another laser, usually dye, laser. excited state A higher energy level that electrons can jump to when energy is added. exothermic When a process gives off energy (gets hot). expectation value equal to the integral of (complex conjugate of psi)A(psi) d(tau). Gives the most probable value for that operator. extensive property any property that depends on the size of the system (m, V) extraordinary ray the beam that is deviant on being split by a birefringent crystal. It is parallel to the ordinary ray. family The same thing as a "group" (see above) faraday the total charge of a mole of electrons; 96,500 coulombs. faraday cap used as a collector for the direct detection of a current of charged particles FEP free energy perturbation Fermi resonance the term given to accidental degeneracy arising in polyatomic molecules in which two different vibrational states accidentally possess approximately the same energy and interact with each other. ferromagnetism when paramagnetic solids align such that the spins are oriented along the magnetic field. first law of thermodynamics The energy of the universe is constant. It's the same thing as the Law of conservation of energy. first law of thermodynamics the internal energy of a system is constant unless changed by doing work or heating. संलयन fission A nuclear reaction where a big atom breaks up into little ones. This is what happens in nuclear power plants. flame emission spectroscopy (FES) burn the sample and measure the spectral lines emitted from the elements. This method is only good for doing an elemental analysis on elements that are easily excited. flame ionization detector when you burn the gas coming out of a GC, any organics present will be ionized. Through the use of electrodes in a detector, the current caused from the presence of these ions can be measured with high sensitivity. flow injection analysis (FIA) when streams of reagents are mixed together and cause a chemical reaction which quickly passes into a detector; mostly handy for studying the dynamics of a reaction that happens on a microsecond timescale or more. fluence refers to the energy density from an optical souce impingent on a sample. The higher the energy density, the higher the fluence. fluorescence spontaneously emitted radiation which ceases immediately after exitation ceases. Comes from electonic transitions in which there is no change in multiplicity. fluorolube a mixture of fluorinated hydrocarbons used as a mulling agent for solids in IR spectroscopy, specially formulated to obtain the spectrum in which Nujol absorption bands appear. fluorophor any molecule in an excited state which is capable of exhibiting fluorescence. force field a kind of calculation which is used in molecular dynamics. The calculation is semi-empirical, which means that the wavefunctions of the system are not determined. FRAP fluorescence recovery after photobleaching मुक्त उर्जा free energy also called "Gibbs free energy", it's the capacity of a system to do work. free inductance decay (FID) a measure of how fast magnetic relaxations take place; an exponentially decaying sine wave with the frequency equal to the difference between the applied frequency and the resonance frequency for that nucleus. free radical An atom or molecule with an unpaired electron. They're way reactive. Fresnel lens an aspheric lens whose surface is broken up into many concentric annular rings. Each ring refracts incident rays to a common focus, so that a very large-aperture and small f-number thin aspheric lens results. Not to be used for precision focusing applications. fullerene onions round fullerenes whith several layers of carbon on top of one another. fullerenes also called buckyballs, these are an elemental form of carbon consisting of some closed surface with no degrees of unsaturation. The most well-known of these is buckminsterfullerene, C60. Related to carbon nanotubes. functional group A generic term for a group of atoms that cause a molecule to react in a specific way. It's really common to talk about this in organic chemistry, where you have "aldehydes, carboxylic acids, amines" and so on. G2 calculations an ab initio method for determining the entropies and enthalpies of reaction from the Schrodinger equation. galvanic cell electrochemical cell that produces electricity spontaneously galvanometer consists of a coil of wire suspended in the magnetic field of a permanent magnet. When current flows through this coil of wire, the magnetic field exerts a torque on the loop, which is opposed by a spring. When you attach a pointer to this coil, you get an analog readout of the current. गामा किरण gamma ray High energy light given off during a nuclear process. When a nucleus gives off this light, it goes to a lower energy state, making it more stable. gangue material of no value that accompanies the desired material in raw ores. Gaussian broadening when broadening comes from the varying Doppler shifts of emitting species in a gas. geisser tubes gas discharge tubes constructed to concentrate the discharge in a capillary tube joining two glass bulbs containing the anode and cathode. The tubes are operated by induction coils and produce intense glow discharges when small quantities of gases or vapors are contained inside the tube. gel a semi-rigid mass of a lyophilic sol in which the dispersion medium has been absorbed by the sol molecules GEMC the Gibbs Monte Carlo computer simulation technique; can use to simulate data on the coexisting vapor and liquid phases of a material at a given temperature. geminate united or arranged in pairs geodesic the shortest distance between two points on a sphere geometrical isomer isomerism where atoms or groups of atoms can take up different positions around a double bond or a ring. This is also called cis- trans- isomerism. g-factor a measure of how much the spin magnetic moment interacts with the local magnetic field. Used in ESR. glass transition when a supercooled liquid becomes a glass; this is not a real phase change but represents a slowing down of the fluid relaxational motion to a point where the relaxation time is far greater than the time of observation. Not a sharp transition. globar emits radiation from 4-15 microns. Bonded SiC rod five cm. long and 5 mm. diameter operated at 1500K. Accurately simulates a blackbody emitter. graft terpolymers a polymer backbone onto which are grafted two series of chemically dissimilar sidechains. Depending on what these sidechains are, they can either order into periodic forms or remain microscopically mixed. Gran plot measures the volume of acid or base or any substance to be titrated versus the volume of titrant added. ground state The lowest energy state possible for an electron. group A column (the things up and down) in the periodic table. Elements in the same group tend to have the same properties. These are also called "families". अर्ध आयु half-life The time required for half of the radioactive atoms in a sample to decay. When talking about chemical reactions, it's the amount of time required to make half the reagent react. half-reaction The oxidation or reduction part of a redox reaction. half-wave plate a crystal that rotates the polarization of light by 90 degrees. हैलोजन halogen The elements in group 17. They're really reactive. उष्मा heat The kinetic energy of the particles in a system. The faster the particles move, the higher the heat. heat of reaction The amount of heat absorbed or released in a reaction. Also called the "enthalpy of reaction" Heisenberg uncertainty principle (deltax)(deltap)>h/2pi; (deltaE)(deltat)>h/2pi Helmholtz coil an electromagnet wound around a charged-particle optical detector used to cancel out the effect of the earth’s magnetic field. Requires two coils. हेस का नियम Hess's Law The enthalpy change for a change is the same whether it takes place in one big step or in many small ones. Heterogeneous catalysis A process where you have one material supporting the actual catalyst for a reaction. One common example is where a porous inorganic material (such as a zeolite) supports small metal particles. Through using small particles, you maximize the catalyst surface area, making it more efficient. heterogeneous mixture A mixture where the substances aren't equally distributed. hexapole selection a method by which molecules can be oriented in space; this can be used to set the up-down symmetry. HFCC hyperfine coupling constant hohlraum a laboratory device to produce blackbody radiation. Consists of a closed metal tube, blackened on the inside, with a narrow slit cut into one of the flat ends. On heating the tube the radiation escaping from the slit is virtually identical with that expected from a blackbody. HOMCOR homonuclear correlated spectroscopy; a 2-D NMR technique. homogeneous mixture A mixture that looks really "smooth" because everything is mixed up really well. homotopic protons that are interchangeable through an axis of symmetry. The chemical shift of these protons is the same in any environment. hot mirror reflect IR light and transmit visible. हुन्ड का नियम Hund's rule The most stable arrangement of electrons occurs when they're all unpaired. HWOT half-wave optical thickness hybrid orbital An orbital caused by the mixing of s, p, d, and f-orbitals. hydration When a molecule has water molecules attached to it. hydrocarbon A molecule containing carbon and hydrogen. hydrodynamics the study of fluid in motion hydrogen bond The tendency of the hydrogen atom stuck to an electronegative atom to become attracted to the lone pair electrons on another electronegative atom. It's a pretty strong intermolecular force, which explains why water has such a high melting and boiling point. hydrogenation When hydrogen is added to a carbon-carbon multiple bond. hydronium ion The H+ ion, made famous by acids. hydroxide ion The OH- ion, made famous by bases. hyperchromic effect an increase in absorption intensity; if structural modification leads to an increase in the molar extinction coefficient for a particular chromophoric group it is said to have brought about a hyperchromic effect. hyperfine structure the multiplet of peaks you see in the ESR spectrum. The source of this splitting is the magnetic field arising from nuclear magnetic momets within the molecule. Generally, for molecules with a spin of I, you see 2n+1 peaks coming from the splitting. The appearance of the peaks is governed by pascal’s triangle, much like the fine structure in NMR. hyperpolarizability the second order polarizability of a molecule. It describes how easily you can push or pull electrons around the molecule. A high hyperpolarizability is good if you want to detect second order processes like second harmonic generation. hypochromic effect a decrease in absorption intensity. hypsochromic shift the shift of an absorption to a shorter wavelength due to substitution or solvent effect (blue shift). hysteresis the tendency of a magnetic substance to remain in a certain magnetic condition Hyugen’s principle every point on a wave front can be considered as a source of tiny wavelets that spread out in the forward direction at the speed of the wave itself. The new wave front is the envelope of all these wavelets.
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