Experiment #4. Elements and Compounds. Goals To practice naming and classifying elements and compounds Background Properties of Elements Elements on the periodic table can be classified as metals, non-metals or metalloids. The zigzag line on the table separates the metals from the nonmetals. The metals make up over 75% of known elements and are found on the lower left side of the table. Metals are shiny, good conductors of heat and electricity, and malleable (can be pounded into sheets). Nonmetals are found on the upper right corner of the periodic table. Nonmetals are dull, poor conductors of 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 between metals and nonmetals. They tend to be shiny, brittle, and average conductors of heat and electricity. Elements can also be categorized by their group. The word periodic refers to the fact that properties of elements in the table repeat. Elements are arranged in columns, or groups, on the periodic table where all elements in the group have similar properties. For instance, all elements in group 8A, the noble gases, are unreactive. Elements in group 1A, the alkali metals, are highly reactive and produce hydrogen when mixed with water. Other named groups include the alkaline earth metals (2A), the halogens (7A), and the transition metals (elements in the block between 2A and 3A). Compounds When two or more elements come together, a chemical compound is formed. In this lab you will practice naming compounds. Naming Compounds Many everyday and compounds have common names. For example, water is the common name for H 2 O, baking soda is the common name for NaHCO 3 . However, there are too many compounds (80 million +) for memorizing common names to be practical so chemists have developed rules for naming. In this exercise you will practice rules for naming simple ionic and covalent compounds and learn to predict the ratios that chemicals combine in based on their ionic charge.
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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.
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
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.
+)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.