Chemistry - an illustrated guide to science (794128), страница 18
Текст из файла (страница 18)
If the solution containssulfate ions, a white precipitate ofbarium sulfate is formed.© Diagram Visual Information Ltd.5 Calcium hydroxide[Ca(OH) 2] test for carbondioxide gas10 4PATTERNS—METALSKey wordsactinidescatalystorbitaloxidation stateshelltensile strengthtransition metalsThe transition metals:electron structureTable to show the electron structures of atoms and ions ofelements from scandium to zincElementSymbolElectronicstructureof atomCommonionElectronicstructureof ionScandiumSc(Ar)3d 14s2Sc3+(Ar)TitaniumTi(Ar)3d 24s2Ti 4+(Ar)VanadiumV(Ar)3d 34s2V3+(Ar)3d 2ChromiumCr(Ar)3d 54s1Cr 3+(Ar)3d 3ManganeseMn(Ar)3d 54s2Mn2+(Ar)3d 5IronFe(Ar)3d 6 4s2Fe2+(Ar)3d 6Fe3+(Ar)3d 5Characteristics oftransition metals© Diagram Visual Information Ltd.● Thetran sition m etals are any of themetallic elements with an incompleteinner electronic structure.
While theoutermost shell contains at most twoelectrons, their next-to-outermostshells have incompletely filled orbitals,which fill up going across a period.The filling is not always regular.● The 40 transitional metals areorganized into four series: The firstseries, shown in the table, runs fromelement 21 (scandium) to element 30(zinc) and is in period 4.
The secondseries, elements 39 (yttrium) to 48(cadmium), is in period 5. The third,elements 71 (lanthanum) to 80(mercury), is in period 6. The fourthseries, from 103 (lawrencium) to 112(ununbium), is the actin ides andtransactinides.● Moving away from the nucleus,successive electron shells becomeprogressively closer in energy. Theenergy levels of the third and fourthorbitals are close in the first series oftransition metals.● The electronic structure of all of theelements in period 4 can be written asthat of the element argon togetherwith additional electrons filling the 3dand 4s orbitals (see table).● Transition metals often have coloredcompounds because their ions containelectrons in the 3d orbitals that canmove between energy levels, givingout light.● Transition metals tend to have highten sile stren gth (the maximum stress amaterial can withstand withoutbreaking), density, and melting andboiling points.
They have a variety ofdifferent oxidation states and areoften good catalysts.CobaltCo(Ar)3d 74s2Co2+(Ar)3d 7NickelNi(Ar)3d 8 4s2Ni 2+(Ar)3d 8CopperCu(Ar)3d 10 4s1Cu+(Ar)3d 10Cu2+(Ar)3d 9Zn2+(Ar)3d 10ZincZn(Ar)3d 10 4s2(Ar) = electron structure of argonNote: As the shells of electrons get further and further from the nucleus successive shellsbecome closer in energy10 5The transition metals:ionization energies andphysical propertiesPATTERNS—METALSKey wordsboiling pointconductorionization energymelting pointtransition metals1 Graphs showing the second and third ionization energies ofthe elements from scandium to zinc1 Ionization energies● Ion ization40 0 0third ionizationenergyCu350 0ZnNiCoMnKJmol–1Cr30 0 0VFeTc250 0ScCu20 0 0Cr150 0TiVMnFeCoNiZnsecond ionizationenergySc10 0 050 020222426283032en ergy is the energyneeded to remove an electron from aneutral gaseous atom or ion againstthe attraction of the nucleus.● The second ionization energy is theenergy needed to go from M + to M 2+ ,(where M = metal), and the thirdionization energy is the energy neededto go from M 2+ to M 3+ .● The second ionization energyincreases across period 4 becausethere is an increasing positive chargeon the nucleus of the ion, making itincreasingly more difficult to removethe second electron.● The third ionization energy for allelements is significantly higher thanthe second.
Removal of the secondelectron results in a greater netdifference between the positive chargeon the nucleus of the ion and thenegative charge surrounding it, so itrequires more energy to remove athird electron.2 Physical propertiesAtomic number2 Physical properties of the elements from scandium to zincElementAtomicradius/ nmm.p./ °Cb.p./ °CDensity/gcm–3Ionic radius/ nmM 3+M2+ScandiumSc0 .16154027303.0TitaniumTi0 .15168032604.50 .0 900 .0 76VanadiumV0 .14190 0340 06.10 .0 880 .0 74Chromium Cr0 .13189024807.20 .0 840 .0 69Manganese Mn0 .141240210 07.40 .0 800 .0 66IronFe0 .13154030 0 07.90 .0 760 .0 64CobaltCo0 .13150 0290 08.90 .0 740 .0 63NickelNi0 .13145027308.90 .0 720 .0 62CopperCu0 .1310 80260 08.90 .0 70ZincZn0 .134209107.10 .0 740 .0 81other metals, tran sition m etalsare good con du ctors of both heat andelectricity.● The transition metals in general havehigher m eltin g poin ts and boilin gpoin ts than groups 1 and 2 metals.● The atomic radii and ionic radii for theM 2+ ion decrease across period 4because the increasing positive chargeon the nucleus of the atom and of theion provides a greater attraction forthe surrounding electrons.© Diagram Visual Information Ltd.● Like10 6PATTERNS—METALSKey wordsacidalkalialuminumamphotericcryoliteelectrolysiselectrolytefiltrateoreprecipitate1 Extractionthe ore from whichalu m in u m is obtained, containsimpurities, principally iron(III) oxide( Fe2O3), that must be removed beforethe ore can be processed to obtainaluminum.● Aluminum oxide is an am photericoxide (it reacts with both acids andalkalis).
After grinding, the ore ismixed with an excess of sodiumhydroxide solution, forming sodiumtetrahydroxoaluminate(III) solution.● Iron(III) oxide and the otherimpurities remain undissolved in thesodium hydroxide solution and arefiltered off.● The filtrate, containing sodiumtetrahydroxoaluminate(III), istransferred into a precipitation tank,where the solution decomposes,giving a precipitate of pure solidaluminum oxide.Aluminum1 Extraction of pure aluminum oxide (Al2 O3)Addition ofNaOH solutionFilter to removeFe2O3 and otherinsoluble matterBauxite(impure Al 2O3)● Bauxite,GrinderReactorAl(OH) 3precipitateSeed crystals orcarbon dioxideaddedHeater todecomposeAl(OH) 3Filter toobtain Al(OH) 3Solid Al(OH) 3Pure Al 2O32 The electrolytic manufacture of aluminum2 Manufacture© Diagram Visual Information Ltd.● Aluminumoxide is reduced byelectrolysis in a Hall-Hérault cell.● For electrolysis to occur, theelectrolyte must be molten so that theions are mobile and able carry electriccharge.
The electrolyte consists of asolution of aluminum oxide andmolten cryolite (a compound ofaluminum fluoride and sodiumfluoride).● Aluminum oxide dissociates in thecryolite solution, giving aluminumions, Al 3+ , and oxide ions, O2- .● Aluminum ions are reduced toaluminum metal, which is tapped offmolten from the bottom of the cell.Oxide ions are oxidized to oxygen.● The graphite anode readily reacts withthe oxygen produced to give carbondioxide. The graphite anode isgradually eaten away and must bereplaced at regular intervals.+aa–bcfdgea graphite anodesb solid crust of electrolytec molten electrolyte(aluminum oxide dissolved in cryolite)defgmolten aluminum oxidetapping holegraphite lining to cell (cathode)insulation10 7Iron: smeltingPATTERNS—METALSKey words1 The blast furnacefluxorereducing agentreductionslagiron ore, coke, and limestonesmeltinghot gasoutlet1 The blast furnace● Ironburning coke acts asa reducing agent725°C1,225°C1,725°Cmolten slaghot airmolten ironmolten ironoutlet2 Table of impurities of pig ironImpurity% impurityin pig ironCarbon3 to 5Silicon1 to 2Sulfur0 .0 5 to 0 .10Phosphorus0 .0 5 to 1.5Manganese0 .5 to 1.02 Impurities● Theiron that leaves the blast furnace(called pig iron) contains a variableamount of impurities, includingcarbon, silicon, sulfur, phosphorus,and manganese.© Diagram Visual Information Ltd.425°Cores such as hematite andmagnetite contain oxygen.
To createpure iron, the ores are smelted in ablast furnace to remove the oxygen.● A charge of iron ore, limestone, andcoke is fed into the top of the furnace,and hot air is blown in toward thebottom through pipes called tuyeres.● The coke is used as a fuel, as aredu cin g agen t, and also to supplycarbon, which dissolves in the molteniron formed.● The limestone acts as a flu x (cleaningagent), combining with acidicimpurities in the iron ore to form aliquid slag (the waste produce ofsm eltin g).● Molten iron falls to the bottom of thefurnace, where it is tapped.● Molten slag floats on the molten ironand is drawn off.● Hot gases (carbon monoxide, carbondioxide, sulfur dioxide, nitrogen, andunreacted oxygen) are removed at thetop of the furnace.● The conversion of iron oxide to iron isa redu ction .
The main reducing agentis carbon monoxide.● Iron oxide is reduced to iron bycarbon monoxide, which itself isoxidized to carbon dioxide.● The temperature inside the blastfurnace is sufficient to decomposelimestone into calcium oxide andcarbon dioxide. Calcium oxide thencombines with impurities such assilicon dioxide to form slag.10 8PATTERNS—METALSKey wordsalloyslagThe manufacture of steel1 Basic oxygen processpig iron1 Basic oxygen process● Steelis an alloy of iron, carbon, andother metals and non-metals.● In the basic oxygen process, thefurnace is charged with controlledamounts of steel scrap and molteniron from a blast furnace.
An oxygenlance, cooled by circulating water, islowered into the furnace, and highpurity oxygen is injected into thevessel at twice the speed of sound.Impurities are readily oxidized. Molteniron is also oxidized.● With the exception of carbonmonoxide, the remaining oxides allreact with calcium oxide, which isadded during the oxygen blow, to forma slag.● The resulting steel is highly oxidizedand not suitable for casting. It isdeoxidized by adding controlledamounts of aluminum and silicon in aseparate reaction vessel.
Additionalmetals and non-metals are added atthis point to make different types ofsteel.tuyeres(pipes)Charging the convertercompressed airenters herePosition during blowing2 Electric arc furnace© Diagram Visual Information Ltd.● Theelectric arc furnace process usesonly cold scrap metal. The furnace is acircular bath with a moveable roofthrough which carbon electrodes canbe raised or lowered as required.● Scrap steel is placed in the furnace,the roof closed, and the electrodeslowered into position. When a currentis passed, an arc forms between thescrap steel and the electrodes, and theheat generated melts the scrap steel.● Lime, fluorspar, and iron ore areadded, and these combine withimpurities forming a slag.
When thesteel has reached the correctcomposition, the slag is poured off,and the steel is tapped from thefurnace.Discharging the slagDischarging the steel2 Electric arc furnacegraphite electrodespower cablesrefractory liningswivel roofwater-cooled furnace roofwater-cooled panelsfurnacefurnace doorrefractory liningtapping spoutsteel scrap10 9RustingPATTERNS—METALSKey words1 Rust experimentTube ATube Bgalvanizinghydroxide ionironmagnesiumrustTube CanhydrouscalciumchlorideoilRustingironnail● RustingairboiledwaterwaterNo rustNo rustRustis the result of a chemical cellbeing formed on the surface of ironwhen it is in contact with water andoxygen from the air.1 Rust experiment● The2 Chemical processairdissolved oxygenFe(OH) 2water filmFe2O3.xH2 O(rust)Fe2+2OH–1+H2O + 2 O2+2e–Feiron (or steel)2e–anodic areacathodic areaelectron flow3 Rust preventionexperiment at left proves thatboth water and oxygen are needed forrusting.● Tube A: When water is boiled, the air itcontains is expelled, and oil preventsany air redissolving in the water.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
