Chapter 3 : Molecules, Compounds and Chemical Equations

Chapter 3 : Molecules, Compounds andChemical EquationsOutline1) Chemical Bonds2) Chemical Formulas and Molecular Models3) Ionic Compounds4) Molecular Compounds5) Formula Mass6) Composition of Compounds7) Writing and Balancing Chemical Equations

Hydrogen, Oxygen and Waterelements combine together to make an almost limitlessnumber of compoundsthe properties of the compound are totally different fromthe constituent elementsChemical Bonds

Chemical Bonds•compounds are made of atoms held together bychemical bondsChemical Bonds

Types of Chemical Bondstwo general types of bonding between atoms found incompounds, ionic and covalentionic bonds result when electrons have been transferredbetween atoms, resulting in oppositely charged ionsthat attract each othercovalent bonds result when two atoms share some oftheir electrons.Chemical Bonds

Chemical FormulasChemical Formula – a symbolic representation designed toindicate (at a minimum) the elements present and the relativenumber of atoms of each element.Three kinds of chemical formulas1)Empirical Formula2)Molecular Formula3)Structural FormulaRepresenting Compounds

Empirical Formulas – simplest formula for a compound;gives the types of atoms present and their relativenumbers.Molecular Formulas – based on an actual (existing)molecules.Empirical and molecular formulas give no info on howthe atoms are attached to each other.Structural Formulas – shows the order in which atoms arebonded together in a molecule and what types of bonds.There are different types of structural formulas.Representing Compounds

Example Ethylene Glycol (1,2 - ethanediol)Empirical Formula – CH 3 OMolecular Formula – C 2 H 6 O 2Structural FormulasOHOHH 2 C CH 2StructuralmodelBall and Stick modelSpace FillingmodelCondensedstructuralmodelCH 2 (OH) CH 2 (OH)Representing Compounds

Elements and Compoundsatomic elements molecular elements molecular compounds ionic compoundsElements and Compounds

Molecular ElementsElements and Compounds

Compound Ionic or Molecular ?CaBr 2Fe 2 O 3PCl 5AlCl 3H 2 OElements and Compounds

Ionic Compounds and their Formulas•metals + nonmetals•no individual molecule units, instead have a 3-dimensional array of cations and anions made offormula units• many contain polyatomic ionsseveral atoms attached together in one ionElements and Compounds

Ionic CompoundsExample : Sodium Chloride• Each Na + ion is surroundedby six Cl - ions (and viceversa)• Can’t assign one Cl - ionexclusively to one Na + ion• Ratio of Na + to Cl - is 1:1Ionic Compounds

Ionic Compounds : Formulas• compound must have no total charge, thereforewe must balance the numbers of cations andanions in a compound to get 0 for a net charge.•if Na + is combined with S 2- , you will need 2Na + ions for every S 2- ion to balance thecharges, therefore the formula must be Na 2 S.Ionic Compounds

Old Exam QuestionIonic Compounds

Naming Ionic Compounds1 st Make sure the compound is ionic !!2 nd Identify the and name the cationMetal that forms only one type of cation.Metal that forms more than one type of cation.3 rd Identify and name the anionNon-metals that form simple anions4 th Combine cation and anion names.Ionic Compounds

CationsMetals with Invariant ChargeGroups 1A +1 & 2A +2 ,Al +3 , Ag +1 , Zn +2 , Sc +3Ionic Compounds

Metals whose ions can havemore than one possible chargeMetals with VariableChargesdetermine charge bycharge on anionIonic Compounds

AnionsSimple AnionsRecognized as single, nonmetalsin an ioniccompound.Ionic Compounds

Polyatomic AnionsPolyatomic ions consist oftwo or more atoms,covalently bonded together,that carry an overall charge(usually negative)Ionic Compounds

Name the following compounds1.NaF2.Au 2 S 33.PbBr 24.Na 2 SO 45.Fe(ClO 3 ) 26.NH 4 Cl7.PCl 5Ionic Compounds

Polyatomic Ions and Oxyanions-Seldomly carry the suffix “ide” (Exceptions are OH -1 and CN -1 )- Often end in “ite” or “ate” and have prefixes “hypo” or “per”- The names of oxygen polyatomics (often called oxoanions)are related to the number of oxygen atoms in the ion.Formula # of oxygens NameClO -1hypochloriteClO-12ClO-13ClO-14chloritechlorateperchlorateIonic Compounds

All common oxyanions of Cl, Br and I carry a charge of -1Some series of oxoanions also contain varying numbersof H atoms and are named accordingly.- The prefix thio indicates that asulfur atom has replaced in oxygenatom.Ionic Compounds

Hydrates• hydrates are ionic compounds containing aspecific number of waters for each formulaunit• water of hydration often “driven off” byheating• in formula, attached waters follow ∙ CoCl 2 ∙6H 2 O• in name attached waters indicated by suffix -hydrate after name of ionic compound CoCl 2 ∙6H 2 O = cobalt(II) chloride hexahydrate CaSO 4 ∙½H 2 O = calcium sulfate hemihydrateHydrateCoCl 2 ∙6H 2 OAnhydrousCoCl 2PrefixhemiNo. ofWaters½mono 1di 2tri 3tetra 4penta 5hexa 6hepta 7octa 8Ionic Compounds

Molecular Compounds1 st Make sure the compound is a molecular compound2 nd Write the name of first element in formula3 rd Write the name of the second element in the formula with an-ide suffix4 th Use a prefix in front of each name to indicate the number of atomsUse a prefix in front of each name to indicate the number of atomsMolecular Compounds

Number Greek Prefix1 Mono2 Di3 Tri4 Tetra5 Penta6 HexaFormulaH 2 ONH 3H 2 O 2Common nameWaterAmmoniaHydrogen peroxideMolecular Compounds

Binary Acids-Acids are species that produce hydrogen ions when dissolved inwaterExample : HCl(aq) H + (aq) + Cl - (aq)-Binary acids have the general formula H a X-(aq) stands for aqueous (Latin for dissolved in water)-Because binary acids are so important we wish to emphasizetheir acidity with special names.-Use the Greek prefix hydro-Follow with the name of the other non-metal using the suffix “ic”Molecular Compounds

ExamplesHF (aq)HCl (aq)HBr (aq)HI (aq)HFHClHBrHIMolecular Compounds

Oxyacids- Contain three different elements (one being hydrogen, onebeing oxygen and the third another non-metal)- Basically the same rules used for oxyanions…except….- The suffix “ous” is used in place of “ite” and…- The suffix “ic” is used in place of “ate”Examples of oxyacids and their namesOxyanion Formulaof saltName of saltFormulaof acidName of acidClO -1 NaClO HClOClO-12 NaClO 2 HClO 2ClO-13 NaClO 3 HClO 3ClO-14 NaClO 4 HClO 4Molecular Compounds

Acid Formulas from Names•when name ends in acid, formulas starts with H•write formulas as if ionic, even though it is molecular•hydro prefix means it is binary acid, noprefix means it is an oxyacid•for oxyacid, if ending is –ic, polyatomic ion endsin –ate; if ending is –ous, polyatomic ion ends in–ousMolecular Compounds

Formula Mass and the Mole ConceptFormula mass – the mass of a formula unit in atomicmass units. Applies to molecular and ionic compounds•also known as molecular mass or molecular weightThe Mole Concept

One Mole of a compound – contains 6.022 x 10 23formula units (or molecular units for a molecularcompound).Molar Mass – mass of one mole of a compound.Numerically equivalent to the formula mass but withunits of g/mol !The Mole Concept

Chemical CompositionA molecular formula tells how many moles of anatom are in one mole of a molecular compound1 mole of C 2 H 6 O 2Chemical Composition

a) How many moles of ethylene glycol are in 25.00mg ofethylene glycol ?b) How many moles of carbon are in the above sample ?c) How many atoms of carbon are in the above sample ?Molecular Formula – C 2 H 6 O 2The Mole Concept

Percent CompositionChemical Composition

Percent CompositionChemical formulaPercent CompositionThe molecular formula for THC (the active ingredient inmarijuana) is C 21 H 30 O 2 . Calculate the percent mass of C,H,O.Chemical Composition

Working BackwardsPretty easy (after some practise) to get thepercent composition from a known molecularformula.Can you work backwards to get themolecular formula if you know the percentcomposition ?Chemical Composition

Percent CompositionChemical formulaAn unknown compound is analyzed (see later) and determined tobe 57.84 % C, 3.64 % H and 38.52% O (by mass). Can youdetermine the compound’s molecular formula ? See text 109-114.For compound C x H y O z%C MCxHyO z %H MCxHyO Mz %O CxHyOzx = ; y = ; z =100% M 100% M 100% M C H O Chemical Composition

Smallest coefficientDivide equations (1), (2) and (3) by equation (3)C x H y O z = C 4 H 3 OThe result is the empirical formulaChemical Composition

Combustion AnalysisHow percent composition is determined experimentallyChemical Composition

Some Examples to Try1) Diethyl ether is a carbon-hydrogen-oxygen compound.The mass percent of carbon, hydrogen and oxygen are64.82%, 13.60% and 21.58% respectively. What is itsempirical formula ?2)3)Chemical Composition

Chemical Reactions•Reactions involve chemical changes in matter resulting innew substances•Reactions involve rearrangement and exchange ofatoms to produce new moleculesReactants ProductsChemical Reactions

Shorthand way of describing a reactionProvides information about the reactionFormulas of reactants and productsStates of reactants and productsRelative numbers of reactant and productmolecules that are requiredCan be used to determine weights of reactants used andproducts that can be madesymbols used to indicate state after chemical(g) = gas; (l) = liquid; (s) = solid(aq) = aqueous = dissolved in waterChemical Reactions

• methane gas burns to produce carbon dioxidegas and gaseous waterwhenever something burns it combines with O 2 (g)CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O(g)• to show the reaction obeys the Law ofConservation of Mass, it must be balancedCH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g)Chemical Reactions

Rules for Balancing Chemical Equations- You can only change the coefficients.- You can NOT add new atoms or molecules intothe equation (doesn’t apply to REDOX reactions –see later).- You can NOT change the chemical formulas toforce a balanced equation.- Usually done by trial and error (see page 115 fora strategy if you find this tricky at first)Chemical Reactions

Solid cobalt (III) oxide reacts with elemental carbon to produce cobalt andcarbon dioxide.Write a skeletalequationBalance atoms incomplex substancesfirstBalance free elementsby adjusting coefficientin front of free elementIf fractional coefficients,multiply through bydenominatorCheckChemical Reactions

• CH 4 and O 2 are the reactants, and CO 2 and H 2 Oare the products• the (g) after the formulas tells us the state of thechemical• the number in front of each substance tells us thenumbers of those molecules in the reactionCH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g)called the coefficients• this equation is balanced, meaning that there areequal numbers of atoms of each element on thereactant and product sidesto obtain the number of atoms of an element, multiply thesubscript by the coefficientChemical Reactions

Example QuestionsName the following compounds1. NiCl 3 a) Nitrogen iodotrichlorideb) Nickel chloridec) Nickel trichlorided) Nickel(III) chloride2. ClO 2 a) Chlorine dioxideb) Chloro oxygenc) Chloro dioxygend) Chlorite

3. HF a) Hydrofluoric acidb) Hydrogen fluoridec) Monohydrogen fluorided) Monohydrogen monofluoride4. Ca(H 2 PO 4 ) 2 a) Calcium phosphateb) Calcium(II) phosphatec) Calcium dihydrogen phosphated) Calcium(II) dihydrogen phosphate

What is the correct formula for Iron(III) sulfate ?a) Fe 3 (SO 4 ) 3b) Fe 3 (SO 4 ) 2c) Fe 2 (SO 4 ) 2d) Fe 2 (SO 4 ) 3

What is Expected ?1) Match names with symbols for the first 36 elements(e.x. I shouldn’t have to tell you that As = Arsenic)3) Know the names and oxidation states of simple ions(ex. Table 3.1), polyatomic ions (Table 3.3) and oxyacids4) Give the names and formulas of inorganic compounds(i.e. all naming rules covered in Chapter 3)