Chemistry - an illustrated guide to science (794128), страница 35
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Bonds are forces and are caused by electrons.bond angle In a molecule, the angle between the twostraight lines joining the centers of the atoms concerned.bromine (Br) A non-metallic element that is isolated as adark red liquid. It is a very reactive oxidizing agent.brown dwarf A ball of gas like a star but whose mass is toosmall to have nuclear fusion occur at its core.Brownian motion The random movement of particlesthrough a liquid or gas.buckminsterfullerene See buckyball.buckyball The nickname for buckminsterfullerene. Anallotropic form of carbon.
It has a cage-like structure and hasthe formula C50 , C60 , or C70 .burette A long, graduated glass tube with a tap at the lowerend. It is used to measure a volume of liquid accurately.calcium (Ca) A soft, slivery-white metal.calcium carbonate A white solid, occurring naturally inmarble and limestone, that dissolves in dilute acids.carbide A compound that contains carbon and an elementwith lower electronegativity.carbon (C) A non-metallic element whose compoundsoccur widely in nature.carbonate A salt of carbonic acid (containing the ionCO32–).carbon cycle The circulation of carbon through thebiosphere.carbon dioxide (CO2 ) A dense, colorless, odorless gasthat does not support combustion.
It exists in theatmosphere and is instrumental in the carbon cycle.carbonic acid (H2 CO3) A very weak acid formed bydissolving carbon dioxide in water.carbon monoxide(CO) A colorless, odorless, verypoisonous gas. It is sparingly soluble in water.carboxyl group The organic radical –CO.OH.carboxylic acid An organic acid that contains one or morecarboxyl groups.catalyst A substance that alters the rate of a chemicalreaction but remains chemically unchanged by it.catalytic cracking The process used in the petroleumindustry to convert large-chain hydrocarbon molecules tosmaller ones.catenation The formation of chains of bonded atoms.cathode The electrode carrying the negative charge in asolution undergoing electrolysis.cathode rays A stream of electrons emitted from thecathode in a vacuum tube.cation An ion having a positive charge.cellulose A complex carbohydrate that is the maincomponent of the cell walls of plants.centrifuge A machine that rotates an object at high speed.chain reaction A self-sustaining nuclear reaction yieldingenergy and electrons emitted by the fission of an atomicnucleus, which proceeds to cause further fissions.chemical compound A substance composed of two ormore elements linked by chemical bonds that may be ionic orcovalent.chemical energy The energy stored in the bonds betweenatoms and molecules that is released during a chemicalreaction.chemical reaction The process in which one or moresubstances reacts to form new substances.chiral An object or a system that differs from its mirrorimage.chloride A compound containing chlorine and anotherelement.chlorine (Cl) A poisonous, greenish, gaseous element thatis a powerful oxidizing agent.chlorophyll A green pigment found in most plants.
Itabsorbs light energy during photosynthesis.chromatography A technique for separating andidentifying mixtures of solutes in a solution.chromium (Cr) A hard, brittle, gray-white metallic elementthat is very resistant to corrosion and takes a high polish.cobalt (Co) A hard, lustrous, silvery-white metallic elementfound in ores,colloid A substance made of very small particles whose size(1–100 nm) is between those of a suspension and those insolution.compound See chemical compoundconcentration A measure of the quantity of solutedissolved in a solution at a given temperature.conductor A material that is able to conduct heat andelectricity.convection current A circular current in a fluid such as air.coordinate bonding A type of covalent bond in which oneof the atoms supplies both electrons.coordination number The number of atoms, ions, ormolecules to which bonds can be formed.copper (Cu) A pinkish metallic element used widely inalloys and electrical wires.covalent bond A bond formed when two electrons areshared between two atoms (usually between two non-metallicatoms), one contributed by each atom.covalent compound A compound in which the atoms inthe molecules are held together by covalent bonds.crust The outer layer of Earth.cryolite A compound of aluminum fluoride and sodiumfluoride.crystal A substance with an orderly arrangement of atoms,ions, or molecules in a regular geometrical shape.daughter nucleus In radio active decay, the nucleusproduced by the decay of the previous nucleus.© Diagram Visual Information Ltd.KEY WORDS20 0© Diagram Visual Information Ltd.KEY WORDSdehydrating agent A substance that has an attraction forwater and is therefore used as a drying agent.dehydrogenation The chemical process of removal ofhydrogen atoms from a molecule (a form of oxidation),increasing its degree of unsaturation.density The mass per unit volume of a given substance.detergent The term for a synthetic soap substitute.diamond A transparent crystalline allotrope of carbon.
It isthe hardest naturally occurring substance.diatomic molecule A molecule that consists of two atoms.diffusion The process of rapid random movement of theparticles of a liquid or gas that eventually form a uniformmixture.dipole A chemical compound with an unequally distributedelectric charge.disaccharide A sugar molecule formed by a condensationreaction between two monosaccharide molecules.displacement reaction A reaction in which a morereactive substance displaces the ions of a less reactivesubstance.dissociation The breaking down of a molecule into smallermolecules, atoms, or ions.dissolve To add a solute to a solvent to form a uniformsolution.distillation A process in which a solution is boiled and itsvapor then condensed.double bond A covalent bond formed between two atomsin which two pairs of electrons contribute to the bond..dry gas A gas from which all water has been removedductile Capable of being drawn out, shaped, or bent.effective collision A collision that brings about a reaction.electric field A field of force around a charged particle.electrode A conductor that allows current to flow throughan electrolyte, gas, vacuum, or semiconductor.electrolysis The process by which an electrolyte isdecomposed when a direct current is passed through itbetween electrodes.electrolyte A substance that forms ions when molten ordissolved in a solvent and that carries an electric currentduring electrolysis.electron One of the three basic subatomic particles.
Verylight and carrying a negative charge, it orbits around thenucleus of an atom.element A substance that cannot be split into simplersubstances using chemical methods.emulsion A colloidal dispersion of small droplets of oneliquid dispersed within another, such as oil in water or waterin oil.enantiomer One of two “mirror images” of a chiralmolecule.end point The point at which a reaction is complete.endothermic a chemical change during which heat isabsorbed.enthalpy A measure of the stored heat energy of asubstance.enzyme An organic catalyst, made of proteins, that increasesthe rate of a specific biochemical reaction.equilibrium The state of a reversible chemical reactionwhere the forward and backward reactions take place at thesame rate.equivalence point The point at which there are equivalentamounts of acid and alkali.ester A member of a hydrocarbon group that is formed by areaction between a carboxylic acid and an alcohol.ethane (C2 H6 ) A colorless, flammable alkane that occurs innatural gas.ethanol (C2 H5 OH) A volatile, colorless liquid alcohol usedin beverages and as a gasoline octane enhancer.ethene (C2 H4 ) A colorless, flammable unsaturated gas,manufactured by cracking petroleum gas, used in ethanol andpolyethene production.evaporation The change in state from liquid to vapor.exothermic A chemical change resulting in the liberation ofheat.face-centered cubic close packing A crystal structurein which one atom sits in each “face” of the cube.Faraday constant The amount of electricity needed toliberate one mole of a monovalent ion during electrolysis(9.648 670 x 10–4 C mol–1).fatty acid A hydrocarbon chain with a carboxyl group atone end.filtrate A clear liquid that has passed through a filter.filtration The process of removing particulate matter froma liquid by passing the liquid through a poroussubstance.fission A process during which a heavy atomic nucleusdisintegrates into two lighter atoms and the lost mass isconverted to energy.fluorescence The emission of light from an object that hasbeen irradiated by light or other radiations.fluorine (F) A gaseous non-metallic element that ispoisonous and very reactive gas.flux A substance that combines with another substance(usually an oxide), forming a compound with a lower meltingpoint than the oxide.foam A dispersion of gas in a liquid or solid.
Small bubblesof gas are separated by thin films of the liquid or solid.formula mass The relative molecular mass of a compoundcalculated using its molecular formula. The mass of a mole ofthe substance.forward reaction A reaction in which reactants areconverted to products.fractional distillation The separation of a mixture orliquids that have differing but similar boiling points.fullerenes Allotropes of carbon in the form of a hollowsphere (buckyball) or tube (nanotube).functional group The atom (or group of atoms) present ina molecule that determines the characteristic properties ofthat molecule.fusion The process by which two or more light atomicnuclei join, forming a single heavier nucleus. The products offusion are lighter than the components.
The mass lost isliberated as energy.galvanizing The coating of iron or steel plates with a layerof zinc to protect against rusting.gamma radiation Very short-wave electromagneticradiation emitted as a result of radioactive decay.gas One of the states of matter. In a gas, the particles canmove freely throughout the space in which it is contained.Gas is the least dense of the states of matter.20 1KEY WORDSin which the mobile phase is a carrier gas and the stationaryphase is a microscopic layer of liquid on an inert solidsupport.gel A colloidal solution that has formed a jelly. The solidparticles are arranged as a fine network in the liquid phase.geometric isomerism A form of isomerism that describesthe orientation of functional groups at the ends of a bondwhere no rotation is possible.glucose In animals and plants, the most widely distributedhexose sugar and the most common energy source inrespiration.glycogen A polysaccharide composed of branched chains ofglucose, used to store energy in animals and some fungi..gold (Au) A shiny, yellow metallic element used in coins,jewelry, and electrical contacts.grade The concentration of ore in rock.Graham’s law The velocity with which a gas will diffuse isinversely proportional to the square root of its density.graphite A soft, grayish-black, solid allotrope of carbon.ground state The lowest allowed energy state of an atom,molecule, or ion.group The vertical columns of elements in the periodictable.
Elements in a group react in a similar way and havesimilar physical properties.group 1 elements The alkali metals. The elements lithium,sodium, potassium, rubidium, cesium, and francium. Theseelements have one electron in their outer shell.group 2 elements The alkaline earth metals.
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