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TrendsinthePeriodicTableofTheElements Theperiodictableincluded118elements,92ofwhichoccurnaturally.Eachelementisassigned itsownboxinthetablecontainingthatelement’ssymbol,atomicnumber,atomicmass.Theboxesare arrangedinorderofincreasingatomicnumber. Thehorizontalrowsintheperiodictablearecalledperiodsandthesearenumberedbeginningatthe topfrom1downto7. Eachverticalcolumniscalledafamilyorgroupandthesearelabeledusingoneoftwoschemes.The oldersystemassignseachcolumnanumberfrom1to8combinedwitheithertheletterAorB.Anewer systemsimplynumberseachgroupfrom1to18andusesnoletters. 1. Elementsinthesamefamilyhavesimilarchemicalpropertiesbecausetheyhavesimilar outerelectronconfigurations. 2. Aswemovedownachemicalfamilyoracrossaperiod,thereareregularchangesin thesepropertiescalledperiodictrends. 3. Groups1and2ontheleftand13-18ontherightcontaintherepresentativeofthemain groupelements.Group3-12arethetransitionelements.Withinthetransition elementstherearetwohorizontalseriescollectivelycalledinnertransitionelements. Thefirstseries,knownaslanthanides,fitsbetweenelements56and72inthe6th periodandthesecondseries,calledactinides,fitsbetweenelements88and104inthe 7thperiod. About¾oftheelementsaremetals.Propertiesofmetalsinclude: • • • • • Solidsatroomtemp.exceptforHg Generallyshinyorlustrouswhenfreshlycutorpolished Goodconductorsofheatandelectricity Generallymalleable,ductile,flexible Tendtogiveupelectronsduringchemicalreactions TheNon-Metalsarelocatedintheupperrightportionofthetable.Propertiesofnonmetalsinclude: • Usuallygasesorbrittlesolidsatroomtemp. • Solidnon-metalsranginginappearancefromdullorlustrousandtranslucentto apaque • Poorconductorsofheatandelectricity • Duringchemicalchangestendtogainelectronsfrommetalstoformanionsor shareelectronswithothernon-metals 1 Theperiodictableisarrangedaccordingtotheatomicnumberoftheelements.This organizationshowsthatthechemicalandphysicalpropertiesrepeatinaregular,periodic pattern. Anelement’speriodnumberisthesameasthenumberofenergylevelsthatitselectrons occupy. Forthemaingroupelements,thenumberofvalencee-‘sisequaltothegroupnumber(1,2)or equaltothegroupnumberminus10(13-18). AtomicRadius(Size) Anatom’ssizeismeasuredbyit’sradius:thedistancefromthenucleustotheapproximate outerboundaryofthecloud-likeregionofitselectrons Asyougodownagroup,thesizeoftheatomincreases.Thevalencee-‘sarefartherandfarther awayfromapositivenucleusandtheinnerelectronsshieldthevalencee-‘sfromthepositive charge. Acrossaperiod,thesizeofanatomdecreases.Eventhoughthenumberofelectronsincreases, theystayinthesameenergylevel.Theincreasingpositivechargeofthenucleuspullsthe electronscloser,reducingtheatom’ssize. Homeworkpg.34#13,15,16,17 IonizationEnergy Anatomthatgainselectronsbecomesnegativelycharged(anion).Anatomthatloseselectrons becomespositivelycharged(cation).Theenergyrequiredtoremoveane-fromanatomis calledionizationenergy(IE). Ionizationenergy_____________________downagroupand_______________acrossaperiod. 2 ElectronAffinity Electronaffinity(EA)isthechangeinenergythatoccurswhenane-isaddedtotheouter energylevelofanatomtoformananion.AhighEAmeansthatenergyisreleasedwhenan atomgainsane-,andthatitislikelytoformananion.AlowEAmeansthatenergyisabsorbed whenanatomgainsane-,andthatitisnotlikelytoformananion. Electronaffinitygenerally______________________downagroupand____________________acrossa period. 3