Chemistry - an illustrated guide to science (794128), страница 12
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Theyexist as single atoms, and there arevery weak forces of attraction betweenthem. The boilin g poin t of theseelements increases in proportion tothe size of the atom.● The boiling points of the grou p 5 andgrou p 6 hydrides also increases withmolecular size. However, the boilingpoint of water and am m on ia aresignificantly higher than might beexpected when compared to the otherhydrides in their groups.
This is theresult of strong forces of attraction,called hydrogen bonding, betweenwater molecules and betweenammonia molecules.2 Strong bonding betweenwater molecules● Thereare five electrons in the outerorbital of a nitrogen atom. Inammonia, three of the electrons areused in nitrogen–hydrogen bonds,while the remaining two form a nonbonding or lon e pair.● The nitrogen atom in ammonia ismore electronegative than thehydrogen atoms.
The result is that apair of bonding electrons lies nearer tothe nitrogen atom than the hydrogenatom in each nitrogen–hydrogenbond.● This forms a dipole, a chemicalcompound with an unequallydistributed electric charge. Thenitrogen–hydrogen bond is polarized,leaving the nitrogen slightly negative(sometimes shown as !- ) and thehydrogen slightly positive (sometimesshown as !+ ).● The slightly positive hydrogen atom isattracted to the slightly negativenitrogen atom and the non-bondingpair of electrons on neighboringammonia molecules.© Diagram Visual Information Ltd.5068PATTERNS—NON-METALSKey wordsalkalibasecatalysthydridehydrogenhydrocarbonhydroxideoxideperoxide1 Preparation● Water,in the form of steam, can bereduced by either carbon orhydrocarbon s to give hydrogen .● This reaction is used to providehydrogen for the Haber process in theindustrial manufacture of ammonia(See page 74):CH4 (g) + H2O(g)CO(g) + 3H2(g)Basic reactions ofhydrogen1 PreparationA C + H2 OBC7H16 + 7H2O7CO + 15H2C2H2O + 2e–2OH– + H2DZn + 2HClZnCl 2 + H22 Reactions of hydrogenA2 Reactions of hydrogen● Hydrogenforms hydrides with bothmetals and non-metals.● Hydrogen can be used to reduce theoxides of metals that are low in thereactivity series, such as copper(II)oxide.3 The oxidesreacts with oxygen to formboth an oxide (water) and a peroxide(hydrogen peroxide).● Hydrogen peroxide contains anunstable peroxide –O-O- bond.● A variety of substances, includingmanganese(IV) oxide, act as catalyststo break this bond, forming water andoxygen.CO + H2B2Na + H22NaHN2 + 3H22NH3O2 + 2H22H2OCl 2 + H22HClCuO + H2Cu + H2O● Hydrogen3 The oxidesA2Na + 2H2OB2H2O2● All2H2O + O2NaOH + HClNaCl + H2O2NaOH + CuCl 2Cu(OH) 2↓ + 2NaCl5 Acids5 Acids● All© Diagram Visual Information Ltd.MnO24 The hydroxy compounds4 The hydroxy compoundsmetal hydroxides are bases.● Metal hydroxides that dissolve in waterare alkalis.● Sodium hydroxide solution can beused to form precipitates of insolublemetal hydroxides like copper(II)hydroxide.2NaOH + H2acids produce solutions containinghydrogen ions, H+ .1A1B1C1D2A2BHClH+ + Cl –HNO3H+ + NO3–H2SO42H+ + SO4 2–from coalfrom oilelectrolysis of brinelaboratory preparationit reduces other elementsit reduces compound3A water3B hydrogen peroxide4 metallic hydroxides are bases69The gases in airPATTERNS—NON-METALSKey words1 Composition of airargoncarbon dioxidecarbon monoxidecompoundelementmethaneozonepollutantsulfur dioxide1 Composition of air● Airis not a chemical com pou n d but amixture of elem en ts and compounds.The exact composition of air variesslightly from place to place dependingon conditions.
For example, theproportion of carbon dioxide in theair above a forest will be less than inthe air above a city. Trees removecarbon dioxide for photosynthesis,while burning fossil fuels releasescarbon dioxide.NitrogenCarbon dioxideArgonOxygen2 Gases present in cleandry air● CleanGasesSymbol or formulaPercentage of volumeNitrogenN78.0 8OxygenO20.95ArgonAr0.93Carbon dioxideCO20.0 4NeonNeHeliumHeKrptonKrXenonXetraces3 Gases that may be found in polluted airGasesSymbol or formulaExample of sourceAmmoniaNH3Industrial processesCarbon monoxideCOMotor vehicle exhaustMethaneCH4Decay of organic material, passed in windby herbivorous animalsNitrogen oxidesNOxMotor vehicle and furnace exhaustOzoneSulphur dioxideO3SO2Motor vehicle exhaustCoal-fired power stations3 Gases in polluted air● Airmay contain pollu tan ts releasedfrom a variety of sources.● Su lfu r dioxide and nitrogen oxidesdissolve in water in the atmosphereand increase the acidity of rainwater.● Carbon m on oxide is a poisonous gas.If it is inhaled, it bonds onto thehemoglobin in red blood cells andprevents them from transportingoxygen.● Ozon e is essential in the upperatmosphere (ozone layer), where itprevents harmful ultraviolet radiationfrom reaching Earth.
At ground level,however, it is responsible for theformation of smog.● Methan e and carbon dioxide aregreenhouse gases. In the upperatmosphere, they prevent heatradiation from passing out into space,thus causing the global temperature torise.© Diagram Visual Information Ltd.2 Gases present in clean dry airdry air is approximately 80percent nitrogen and 20 percentoxygen.● Argon makes up the largest portion ofthe remaining 10 percent.● Air usually contains water vapor, withthe amount depending on localconditions.70PATTERNS—NON-METALSKey wordsgroup 5nitrogensolubilitytriple bondNitrogen1 Nitrogen atom and moleculeN1 Nitrogen atom andmoleculeis in grou p 5 of the periodictable.
Nitrogen atoms have fiveelectrons in the outer orbital andrequire an additional three electronsin order to fill the shell.● Nitrogen exists as nitrogen molecules,N2, in which each nitrogen atomprovides three electrons. The nitrogenatoms are held together by a triplebon d. A large amount of energy isneeded to break the N!N triple bond(945.4 kJ mol-1), which accounts forthe unreactive nature of nitrogen.NN● NitrogenNitrogen atom,14 N7Nitrogen molecule, N 22 Physical properties of nitrogenPhysicalpropertiesNitrogenm.p./ °Cb.p./ °Cdensity(relativeto air)colorsmellsolubilityat STP–120–1960.97nonenone1.52 cm 3in 10 0 gof water2 Physical properties ofnitrogen● Themelting point and boiling point ofnitrogen are both very low, andnitrogen is only a liquid over a smallrange of temperature.
This indicatesthat the intermolecular forces innitrogen are weak.● The solu bility of gases decreases withincreasing temperature. The solubilityof nitrogen falls from 2.3 cm 3 per 100 gwater at 0°C to 1.0 cm 3 per 100 g waterat 100°C.3 Laboratory preparationof nitrogen● Nitrogenis formed by the thermaldecomposition of ammonium nitrite:3 Laboratory preparation of nitrogen from ammoniumchloride and sodium nitratea ammonium chloride and sodiumnitrate in solutionb heatc sand trayd nitrogene wateradNH4 NO2(s) ➞ 2H2O(g) + N2(g)nitrite is difficult to storebecause it decomposes over time.
It isbest made when it is needed by mixingammonium chloride and sodiumnitrite:© Diagram Visual Information Ltd.● AmmoniumceNH4 Cl(s) + NaNO2(s) ➞NH4 NO2(s) + NaCl(s)b71Other methods ofpreparing nitrogenPATTERNS—NON-METALSKey wordsammoniagroup 8inertnitrogensoluble1 Extraction of nitrogen from the atmospherecafOther methods● Indaddition to preparing n itrogen fromammonium chloride and sodiumnitrate, it can be extracted from the airor from the reduction of copper(II)oxide by am m on ia.dh1 Extraction of nitrogenfrom the atmosphere● Airgbeis approximately 80 percentnitrogen and 20 percent oxygen.Impure nitrogen can be obtained byremoving carbon dioxide and oxygenfrom air.● Potassium hydroxide solution reactswith carbon dioxide:KOH(aq) + CO2(g) ➞ KHCO3(aq)● A hotcopper pile reacts with oxygen:2Cu(s) + O2(g) ➞ 2CuO(s)● Nitrogenprepared in this way containsargon and other grou p 8 gases.However, because these are chemicallyin ert, they would not interfere withany subsequent reactions.2 Preparation of nitrogen from ammoniajif2 Preparation of nitrogenfrom ammonia● Ammoniadcan be used to reducecopper(II) oxide to copper.
Nitrogen isone of the other products of thisreaction:dh3CuO(s) + 2NH3(g) ➞3Cu(s) + 3H2O(g) + N2(g)geabcdefair intakepotassium hydroxide solution to absorb carbonhot copper coil to remove oxygenheatsafety trapdelivery tubeghijwaternitrogen collected over waterdry ammonia gasdry copper(II) oxideis not very solu ble and isreadily collected over water.● Water vapor condenses in the watertrough. Ammonia is very soluble, andunreacted ammonia dissolves in thewater.© Diagram Visual Information Ltd.● Nitrogen72PATTERNS—NON-METALSKey wordsammonianitratenitritenitrogennitrogen cycleThe nitrogen cycleNitrogen cycle schematic13Nitrogen cycleis continually being recycledbetween the soil and the air by naturalprocesses.● Lightning provides the energy foratmospheric nitrogen and oxygen toreact, forming nitrogen oxides.
Forexample:54● Nitrogen82N2(g) + O2(g) ➞ 2NO(g)N2(g) + 2O2(g) ➞ 2NO2(g)● These© Diagram Visual Information Ltd.oxides dissolve in water vaporin the atmosphere and eventually fallto the ground as rain.● Atmospheric nitrogen is alsoconverted into nitrogen compoundsby nitrogen-fixing bacteria found in theroot nodules of some plants.● Nitrogen compounds are released intothe soil as a result of the decay ofanimal waste products and by thedecay of dead plants and animals. Inthe soil, the am m on ia formed duringdecay processes is converted inton itrates by the action of nitrifyingbacteria:Ammonia ➞ Ammonium compounds➞ Nitrites ➞ Nitrates● Nitrogen compounds may also beadded to soil as artificial fertilizers.Ammonium nitrate is widely used byfarmers and gardeners to providegrowing plants with essential nitrogen.● Nitrogen compounds are taken out ofthe soil by plants, which use them tomake proteins and other essentialchemicals.
Animals subsequently eatthe plants.● Nitrogen compounds in the soil areconverted to nitrogen gas bydenitrifying bacteria.76All plants and animals need nitrogen, present in proteins and nucleic acids. Most living things,however, cannot use nitrogen directly from the atmosphere.1 Nitrogen in the air.2 Nitrogen in the atmosphere is trapped bysome plant roots.3 Plants use nitrogen for making proteins.4 Animals eat plant proteins.5 The proteins in dead organisms and in bodywastes are converted to ammonia bybacteria and fungi.6 Other bacteria convert the ammonia tonitrates.7 Artificial nitrates are added to the soil asfertilizer.8 Plants absorb the nitrates.Nitrogen cycle2143578673Preparation andproperties of ammoniaPATTERNS—NON-METALSKey wordsalkaliammoniaammoniumhydroxidebond angle1 Laboratory preparation of ammoniadlone pairshella1 Laboratory preparation ofammonia● Am m on iais formed by the reaction ofan ammonium compound, such asammonium chloride, with an alkali,such as sodium hydroxide:NH4 Cl(s) + NaOH(aq) ➞NH3(g) + NaCl(aq) + H2O(l)● Ammoniagas is dried by passing itthrough a column of calcium oxide.b2 Bonding angle● Theeabcdecsodium hydroxideammonium chlorideheatcalcium oxide for dryingdownward displacement of air2 Bonding angleNHHNHH107°five electrons in the outerelectron shell of nitrogen plus threeshared electrons from the hydrogenatoms form three pairs of bondingelectrons and one pair of non-bondingelectrons (lon e pair).● The four pairs of electrons aredirected toward the corners of atetrahedron.
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