1 group 2 Alevel考试化学课件.pptx

GroupⅡIntroductionGeneralpropertiesoftheGroup2elements

strontiumRedmagnesiumwhiteCalciumBrickredBariumGreenThesemetalsburninairwithcharacteristicflamecolours

Theyareallmetals.Theyaregoodconductorsofheatandelectricity.Theircompoundsareallwhiteorcolourless.Inalltheircompoundstheyhaveanoxidationnumber+2.Theircompoundsareionic.Theyarecalledalkalineearthmetalsbecausetheiroxidesandhydroxidesarebasic.Theyreactwithacidstogivehydrogen.

ComparewithgroupⅠmetalsTheyareharderanddenserTheyhavehighermeltingpointsTheyexhibitstrongermetallicbonding(becausetheyhavetwoouter-shellelectronsinsteadofone)

MagnesiumUSESMagnesiumburnswithabrightwhitelight.Itwasonceusedinphotographicflashbulbs.Magnesiumiswidelyusedtoprotectsteelobjectssuchasships.Magnesiumisalsofoundinchlorophyll,thesubstanceinplantswhichperformsphotosynthesis.

MagnesiumhydroxideUSESMagnesiumhydroxideisaweakalkaliandisusedinindigestionmemedies.Magnesiumhydroxideisaweakalkaliandisusedintoothpastes

MagnesiumoxideMeltingpoint:2852℃Boilingpoint:3600℃USESMagnesiumoxideisarefractorymaterial,whichmeansthatitisresistanttoheat(itsmeltingpointisover3000K).Itsmainuseisfortheliningoffurnaces.

MagnesiumfluorideUSESMagnesiumfluorideisusedtocoatthesurfaceofcameralenses,toreducetheamountofreflectedlight.Itisresponsibleforthevioletcolouronthesurfaceofthelens.

CalciumoxideUSESCalciumoxidewasusedincement,mortarandplastermanufacture.Additionofwatertodrycalciumoxidecausesthesolidtocrumble,inanexothermicreactionproducingcalciumhydroxide.

CalciumoxideCalciumhydroxideCalciumoxideistheoriginofthetheatricalterm‘limelight’,becauseitglowswithabrightwhitelightwhenstronglyheatedanwasoriginallyusedinstagelighting.Calciumhydroxideisalsousedonacidicsoil,toreducetheacidityofthesoil.