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10
PartI
orbitaroundthenucleus.Thenucleusismadeofprotonsandneutrons.(1)
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---.Hydrogenatomhas1electronwhichorbitsthenucleus.Helium
atomhastwoelectrons.Normallyanatomhasanequalnumberofprotons
andelectronsandsotheoverallchargeonamaterialiszero.Wecallsuch
atomsbalancedatoms.However,whenyourubthematerialwithanother
materialsomeelectronsmaymovefromonematerialtotheotherand
consequentlytheybecomecharged,e.g.whenyourubapolyethylenerod
withwool,someelectronsfromwoolmovetothepolyethylenerodandit
becomesnegativelycharged.
Somematerialslettheelectronspassthroughthemeasily,othersprevent
theflowofcharge.Theformerarecalledconductors,thelatterarecalled
insulators.
Conductorsarematerialswhichmaketheflowofcurrentpossible.The
mostpopularconductorinelectricalapplicationsiscopper.Copperatomhas
29electronswhichorbitthenucleusindifferentorbitscalledshells.(2)
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--.Thiselectroniscalledthevalenceelectron.Valenceelectronscan
becomefreeelectronswhentheyreceiveenoughenergyandfreeelectrons
arenecessaryfortheflowofcurrenttotakeplace.
Conductorsareusedtocarrycurrent,whereasinsulatorsareusedto
preventcurrentflow.Theirelectronsaretightlyheldtoatomsandtheyhave
veryfewfreeelectrons.(3)---
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--.
Semiconductorshavefewerfreeelectronsthanconductorsbutmorethan
insulators.(4)---
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--.Buttheyarethebasisformodernelectronic
devices,forexamplethediodeorintegratedcircuit.Siliconandgermanium
areexamplesofsemiconductors.
B.Readthesentencesanddecideiftheyaretrueorfalseandthen
correctthefalsesentences
1.Anatomisthesmallestparticleofanelementthatretainsthe
characteristicsoftheelement.
2.Theelectronisthebasicparticleofpositivecharge.
3.Whenelectronsintheinnermostshellofanatom(valenceelectrons)
breakaway,theybecomeions.
4.Freeelectronsmakecurrentpossible.
5.Silverandcopperarethebestconductors.
6.Siliconandgermaniumarecommoninsulatingmaterials.
7.Insulatorscancarrycurrentbecausetheyhaveveryfewfree
electrons.
