化學(xué)專業(yè)外語課件

Lesoon1

SizeofAtomsandIonsLesoon1SizeofAtomsandIonsThesizeofatomsdecreasesfromlefttorightacrossaperiodinperiodictable.Forexample,onmovingfromlithiumtoberyllium,thenumberofchargesonthenucleusisincreasedbyone,sothatalltheorbitalelectronsarepulledinclosertothenucleus.Inagivenperiod,thealkalimetalisthelargestatomandthehalogenthesmallest.Whenarowoftentransitionelementsorfourteeninnertransitionelementsoccursinahorizontalperiod,thecontractioninsizeisevenmoremarked.Ondescendingagroupintheperiodictablesuchaslithium,sodium,potassium,rubidium,caesium,thesizeoftheatomsincreasesduetotheeffectofextrashellsofelectronsbeingadded;thisoutweighstheeffectofincreasednuclearcharge.Thustheeffectivenuclearchargeisincreasedandtheelectronsarepulledin.

Apositiveionisthereforesmallerthanthecorrespondingatomandthemoreelectronsremoved(thatis,thegreaterthechargeontheion),thesmalleritbecomes.AtomicradiusNa0.157nmAtomicradiusFe0.117nmIonicradiusNa+0.098nmIonicradiusFe2+0.076nmIonicradiusFe3+0.064nmWhenanegativeionisformed,oneormoreelectronsareaddedtoanatom,theeffectivenuclearchargeisreducedandhencetheelectroncloudexpands.Negativeionsarebiggerthanthecorrespondingatom.VanderWallsnon-boundedradiusCl0.140nmIonicradiusCl-0.181nm范德瓦爾斯（1837-1923），荷蘭物理學(xué)家、化學(xué)家、生物學(xué)家，1910年獲得諾貝爾物理獎，他提出了包括氣態(tài)和液態(tài)的“物態(tài)方程”。氫Hydrogen

氦Helium

鋰Lithium

鈹Beryllium

硼B(yǎng)oron碳Carbon

氮Nitrogen

氧Oxygen

氟Fluorine

氖Neon鈉Sodium

鎂Magnesium

鋁Aluminum

硅Silicon

磷Phosphorus硫Sulfur氯Chlorine氬Argon鉀Potassium鈣Calcium碳Carbon

氮Nitrogen

氧Oxygen

氟Fluorine

氖Neon硫Sulfur氯Chlorine氬Argon鉀Potassium鈣Calcium溴bromine碘iodine硒selenium砷arsenic鍺germanium錫tin鉛lead鋅zinc汞mercury銅copper銀silver金gold鎳nickel鉑platinum鐵iron錳manganese鎢tungsten(wolfram)鋇barium鉻chromium鈦titaniumLesson2MetallicCharacter

Metalsareelectropositiveandhaveatendencytolosselectrons,ifsuppliedwithenergy:M→M++e.

Thestrongerthistendency,themoreelectropositiveandmoremetallicanelementis.

Thetendencytolosselectronsdependsontheionizationenergy.Sinceitiseasiertoremoveanelectronfromalargeatomthanfromasmallone,metalliccharacterincreasesaswedescendthegroupsintheperiodictable.

Electropositivityisreallytheconverseofelectronegativity,butitisconvenienttoretaintheconceptofelectropositivitywhendescribingmetals.Stronglyelectropositiveelementsgiveioniccompounds.Metallicoxidesandhydroxidesarebasicsincetheyionize,andgivenhydroxylions:NaOH→Na++OH-CaO+H2O→Ca2++2OH-Thedegreeofelectropositivityisshowninavarietyofways.Stronglyelectropositiveelementsreactwithwaterandacids.Theyformstronlybasicoxidesandhydroxides,andtheyreactwithoxyacidstogivestablesaltssuchascarbonates,nitratesandsulphates.Weaklyelectropositiveelementsareunaffectedbywaterandaremuchlessreadilyattackedbyacids.Theiroxidesarefrequentlyamphoteric,andreactwithbothacidsandalkalis.Theyarenotbasicenoughtoformstablecarbonates.Thedegreeofelectropositivityisshowninavarietyofways.Stronglyelectropositiveelementsreactwithwaterandacids.

Weaklyelectropositiveelementsareunaffectedbywaterandaremuchlessreadilyattackedbyacids.Theyformstronglybasicoxidesandhydroxides,andtheyreactwithoxyacidstogivestablesaltssuchascarbonates,nitratesandsulphates.Theiroxidesarefrequentlyamphoteric,andreactwithbothacidsandalkalis.Theyarenotbasicenoughtoformstablecarbonates.Theelectropositivenatureofametalisalsoshowninthedegreeofhydrationoftheions.Inthechange:

thepositivechargebecomesspreadoverthewholecomplexion.

Sincethechargeisnolongerlocalizedonthemetal,thisisalmostthesameasthechangeM+→M.

Stronglyelectropositivemetalshaveagreattendencytotheoppositechange:M→M+,sothattheyarenotreadilyhydrated.Thelesselectropositivethemetal,theweakerthetendencyM→M+andthestrongerthedegreeofhydration.

ThustheelementsinGroupⅡaremoreheavilyhydratedthanthoseinGroupⅠ,andthedegreeofhydrationdecreasesdownagroup,e.g.and.Saltsofstronglyelectropositivemetalshavelittletendencytohydrolyzeandformoxysalts.Sincethesizeofthemetalionislargeithaslittletendencytoformcomplexes.

Ontheotherhand,saltsofweaklyelectrop