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Experiment#4.ElementsandCompounds.
GoalsTopracticenamingandclassifyingelementsandcompoundsBackgroundPropertiesofElementsElements on the periodic table can be classified as metals, non-metals or metalloids. The zigzag line on the tableseparates themetals from the nonmetals. Themetalsmake up over 75%of knownelements and are foundon thelowerleftsideofthetable.Metalsareshiny,goodconductorsofheatandelectricity,andmalleable(canbepoundedintosheets).Nonmetalsarefoundontheupperrightcorneroftheperiodictable.Nonmetalsaredull,poorconductorsof heat and electricity, and brittle. Metalloids, or semi-metals are located on the zigzag line of the periodic table.Aluminum touches the line, but is considered a metal. Metalloids have properties that are intermediate betweenmetalsandnonmetals.Theytendtobeshiny,brittle,andaverageconductorsofheatandelectricity.
Elementscanalsobecategorizedbytheirgroup.Thewordperiodicreferstothefactthatpropertiesofelementsinthetablerepeat.Elementsarearrangedincolumns,orgroups,ontheperiodictablewhereallelementsinthegrouphavesimilarproperties.Forinstance,allelementsingroup8A,thenoblegases,areunreactive.Elementsingroup1A,thealkalimetals,arehighlyreactiveandproducehydrogenwhenmixedwithwater.Othernamedgroupsincludethealkalineearthmetals(2A),thehalogens(7A),andthetransitionmetals(elementsintheblockbetween2Aand3A).
CompoundsWhen two or more elements come together, a chemical compound is formed. In this lab you will practice
namingcompounds.NamingCompounds
Manyeverydayandcompoundshavecommonnames.Forexample,wateristhecommonnameforH2O,bakingsoda is the common name for NaHCO3. However, there are too many compounds (80 million +) for memorizingcommonnamestobepracticalsochemistshavedevelopedrulesfornaming.Inthisexerciseyouwillpracticerulesfornamingsimpleionicandcovalentcompoundsandlearntopredicttheratiosthatchemicalscombineinbasedontheirioniccharge.
IonicCompoundswithMetalChargesthatDoNotVary
Simple ioniccompoundsare formed fromametalandnon-metal ions. Themetal is thecation,orpositivelycharged ion and the nonmetal is the anion, or negatively charged ion. In the chemical formula, the cation is alwayswrittenfirstandtheanioniswrittensecond.Cationswithchargesthatdon’tvaryincludeGroup1Aalkalimetals,whichalwaysform1+cationsandGroup2Aalkalineearthmetalswhichalwaysform2+cations,andGroup3Ametals,whichalwaysform3+ions.
Toname this typeof ionic compound, the cation getswritten first using its full elementname. The anion is
writtensecondusingthestemofitselementnameandaddingan“ide”ending.Forinstance,fluorinebecomesfluorideandoxygenbecomesoxide.
Examples: NaCl sodiumchloride MgBr2magnesiumbromide
Ionic compounds are electronically neutral, meaning the charges on the anions andcationsbalancetozero.Todetermineaformulafromachemicalname,youmustfirstdeterminethechargesontheionsinthecompoundandthenfigureouthowmanyofeachareneededtobalancethecharges.ForinstancecalciumchlorideismadeofCa2+andCl-ions.ForthechargestobalancethereneedstobetwoCl-ions,thereforetheformulaisCaCl2.
IonicCompoundswithMetalChargesthatVary
Somemetalscanformionswithdifferentcharges.Forinstance,ironinioniccompoundsisfoundasbothFe2+andFe3+.Metalswithchargesthatvaryincludemosttransitionmetals(zinc,cadmiumandsilverareexceptions)plustinand lead. Sincemore than one charge is possible,more than one chemical formula is possible. Iron can form twocompoundswithchlorine:Fe2+formsFeCl2,Fe3+formsFeCl3.Thesetwodifferentcompoundshavedifferentphysicalandchemical properties. For example, FeCl2 has amelting point of 306° C,while FeCl3 melts at 677° C. Therefore,wecannotsimplycallbothcompounds“ironchloride.”
Whennamingcompoundswithmetalthathavevariablecharge,aromannumeralinparenthesesiswrittenafterthemetalnameandindicatedthechargeonthemetal. For instance,Fe2+ iscallediron(II)andFe3+ iscallediron(III).Theanioniswrittenasthe“ide”formoftheelement.
When starting with the formula, the charge of themetal has to be deducedfrom theanion charge. The formulaCuO indicatesoneatomofoxygen carryinga2-charge. In order for the charges to sum to zero, the copper atom must have a 2+.Thereforethenameiscopper(II)oxide.
The formula SnCl4 has 4 chloride ions, each with a 1- charge, so the totalnegativechargeis4-.Thechargeonthetinmustbe4+,sothecompoundisnamedtin(IV)chloride.
IonicCompoundswithPolyatomicIons
Polyatomicionsareionscomposedoftwoormorecovalentlybondedatomsthatcanbethoughtofasasingleunitcarryingacharge. Ioniccompoundsthathavethreeormoreelementsaregenerallycomposedofametalcationandpolyatomicanion.Ammonium(NH4
+)istheonlycommonpolyatomiccation.Thenames,formulasandchargesofpolyatomicionsmustbememorized(seetableofcommonpolyatomicionsbelow).Ioniccompoundswithpolyatomicionsgetnamed in thesamewayasType Iand IIbinary ioniccompoundswith thenameof thepolyatomic ion in theplaceoftheanionname.Ifmorethanonepolyatomicionisneededtobalancethecharges,thewholeiongetsputinparentheses.Examples: Li2CO3 lithiumcarbonate Pb(NO3)2 lead(II)nitrate NH4Cl ammoniumchloride
Ionswith1-charge Ionswith2-chargeNO2
- Nitrite SO32- Sulfite
NO3- Nitrate SO4
2- SulfateClO2
- Chlorite CO32- Carbonate
ClO3- Chlorate
CN- Cyanide OH- Hydroxide Ionswith3-chargeHCO3
- Hydrogencarbonate PO33- Phosphite
PO43- Phosphate
Ionswith1+charge NH4
+ Ammonium
Covalent(Molecular)Compounds
Covalentcompoundsaremadeoftwoormorenon-metals,asopposedtoametalandanon-metal.Thesystemfor naming covalent compounds is different from the one for ionic compounds and it is important to keep the twosystemsseparate.
Tonameacovalentcompound,thefirstelementiswrittenasitselementname,thesecondelementiswrittenasits“ide”form,andbothelementsgetaprefixthatindicatesthenumberofeachelementinacompound.Iftheprefixofthefirstelementismono,theprefixisdropped.
Examples: P2S5 diphosphorouspentasulfide
N2O dinitrogenmonoxide NO2 nitrogendioxide
Prefixes1 mono-2 di-3 tri-4 tetra-5 penta-
6 hexa-7 hepta8 octa-9 nona-10 deca-
Materials: elementvials samplesofCu,Zn,C,Si conductivityprobe Procedure
A.PropertiesofElements 1. Observethepropertiesofvariouselementssamplesinthelabeledbottles.Completelyfillouttheelement
propertiestableinthedatasheet.Ifanelementdoesnotbelongtoanamedgroup,writethegroupnumber(ex4A)inthelastcolumn.
2. Touchthetwowireendsoftheconductivityprobetothefourelementsintheconductivitytable.IftheLEDlights,thecircuitwascompletedmeaningthattheelementconductselectricity.
B.NamingCompounds3. Fill in the tables with the missing name, formula or ion. Refer to naming rules in the lab background or your
textbook.
Name_________________________
TeamName______________________
CHM101Lab–ElementsandCompounds–GradingRubricToparticipateinthislabyoumusthavesplash-proofgoggles,propershoesandattire.
Criteria Pointspossible Pointsearned
LabPerformance
Printedlabhandoutandrubricwasbroughttolab
3
Safetyandproperwastedisposalproceduresobserved
2
Followedprocedurecorrectlywithoutdependingtoomuchoninstructororlabpartner
3
Workspaceandglasswarewascleanedup
1
LabReport
PartA(elements)
3
PartA(conductivity)
2
PartB(Ionic)
4
PartB(Covalent)
2
Total
20
Subjecttoadditionalpenaltiesatthediscretionoftheinstructor.
ElementsandCompounds
ReportPage1of2
A.PropertiesofElements
Element Symbol AtomicNumber
Color ShinyorDull? Metal,nonmetalormetalloid?
GroupName(ornumberifnone)
Aluminum
Bismuth
Carbon
Copper
Helium
Iodine
Magnesium
Mercury
Nickel
Oxygen
Silicon
Sulfur
Tin
Zinc
Element Metal,nonmetalormetalloid? Conductive? Doesresultfityourexpectations?Silicon
Copper
Sulfur
Zinc
ElementsandCompounds
ReportPage2of2
B.CompletethefollowingtableforioniccompoundsFormula cation anion Name
Al2O3 Al3+ O2- aluminumoxide
Cu(NO3)2 Cu2+ NO3- copper(II)nitrate
iron(III)phosphide
Pb2+ Br-
Li2S
potassiumcarbonate
Ni(OH)3
Mg2+ N3-
cesiumnitrite
CoF2
tin(IV)oxide
(NH4)2SO4
calciumcyanide
CompletethefollowingtableofcovalentcompoundsFormula Name
NO2 nitrogendioxide
SO3
diphosphoroustrisulfide
CBr4
oxygendifluoride
IBr