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8-1 CB I Chemical Bonding CHEM101/3, J1 8-2 2007 10 01 Nomenclature & Stoichiometry HT Suitable Textbook Problems General Advice In each section, try the more difficult problems first. If you have difficulties try the simpler ones also, until you are fully proficient with the topic Nomenclature • General 3: 55 - 59 odds • Nomenclature Review Mole Concept • Stoichiometry Review 3: 5 - 13 odds Balancing Chemical Equations Ref Prob 10: 1 - 2 1: 5 - 7 3: 1 - 3, 6 4: 1 - 5 4: 1 - 9 odds Percent Composition 3: 15 - 21, 25 -33 • see list next page • HMWK #4 and #5 Stoichiometry 4: 13 - 21, 27 - 31, 37, 39, 43, 45, 55, 57, 63, 65 Adv Rdg 10: 3 - 4 8-3 8-4 General At STP (standard temp. & pressure), few elements exist as single atoms: N. G., (noble gases) only The rest of the elements have bonds: metals: metallic bond non-metals: covalent bond In compounds, 2 kinds of bonds exist ionic transfer of e–’s covalent Ionic Bonding metal loses e–’s cation non-metal gains e–’s anion Ions held together (bound) by electrostatic (“Coulombic”) forces. Notes: In solids, 3- D lattice (grid, network) exists (no “one - on - one” relationship !) see Pet. Fig. 12.38 sharing of e–’s Driving force: to get “octet” of e–’s = “full shells” =“max Zeff” on each atom ion pairs, Na+ Cl– , may exist in gas state or liquid (molten) phase generally, in aqueous solution cations and anions are separated by H2O 8-5 8-6 Pet. Fig. 12.38 3 - D Lattice of Ionic Solids Covalent Bonding • e–’s shared to get “octet” for every atom • lowest energy at “certain distance” = bond length • this energy = bonding energy, = energy required to separate bonded atoms completely • Ex. Covalent bonding in H2 molecule see Pet. Fig. 11.1 8-7 8-8 Pet. Fig. 3.4 Covalent Bonding in S and P Pet. Fig. 11.1 Covalent Bonding in H2 S8 P4 8-9 1. Know symbol ↔ name & find position in P.T. quickly for Cs Ba HF (aq) __________________ HI (aq) ____________________ 5. Binary Ionic Cmpds first 36 elements plus Sr 8-10 4. Binary acids in H2O: hydro …ic acid Nomenclature Pd Ag Cd Sn Sb Pt Pb Bi Au Hg A. main group elements I Xe U 2. Diatomic/ Multiatomic Elements in their “standard states”: • cation, anion (…ide) • determine charge on ions (group in P.T.) • smallest whole number ratio, balance for electroneutrality = “crossover method” “ Cl i f Br o h n “ → Cl2, I2, F2, Br2, O2, H2, N2 also S8 , P4 3. Binary Covalent Cmpds ( “nonmetal + nonmetal”) • less electronegative element first • more electronegative element second (ending …ide) • use Latin/Greek prefixes ((mono), di, tri, tetra, penta, hexa, hepta, octa, CaO _____________________ beryllium fluoride ____________ SrI2 _____________________ magnesium nitride ____________ K2S _____________________ barium sulfide ____________ B. transition metals, also Sn, Pb nona, deca) CO ____________________ SF6 ____________________ P4O10 ____________________ Indicate charge on cation w/ Roman numeral TiCl4 _____________________ chromium(II) chloride ___________ NiS _____________________ copper(I) oxide ____________ Fe2S3 _____________________ iron(III) sulfide ____________ 8-11 8-12 8. Acidic Anions 6. Standard Oxoacids & Derived Anions H2CO3 carbonic acid CO32– carbonate HNO3 nitric acid NO3– ______________ HSO4– _____________________ sodium hydrogen sulfate _________ H3PO4 phosphoric acid PO43– ______________ NaHSO3 ____________________ dihydrogen phosphate anion ______ H2SO4 sulfuric acid SO42– ______________ K2HPO3 ____________________ sodium hydrogen carbonate _______ HClO3 chloric acid ClO3– ______________ HBrO3 bromic acid BrO3– _______________ HIO3 IO3– (incomplete loss of H from acid): hydrogen ….ate, ite, … 9. Hydrates: indicate # of H2O by Greek/Latin letters CuSO4 • 5H2O copper(II) sulfate pentahydrate iodic acid _______________ Na2SO4• 10H2O _______________________________________ 10. Special Cases 7. More or Less O than “standard” acid/anion 2 less O : hypo…..ous acid; 1 less O : …..ous acid; 1 more O: per…..ic acid; hypo…..ite …..ite per…..ate HClO2 _____________________ potassium perchlorate ___________ HIO4 _____________________ sodium nitrite ____________ HNO2 _____________________ sodium sulfite ____________ KBrO _____________________ ammonium phosphite ___________ NH3 ammonia OH – NH4+ ammonium CN – H2O water C2H3O2– acetate cyanide MnO4 H2O2 hydrogen peroxide HC2H3O2 (= CH3CO2H) hydroxide acetic acid – 2– CrO4 permanganate chromate Cr2O72– dichromate 8-13 8-14 4. Binary acids in H2O: hydro …ic acid Nomenclature w/ Answers HF (aq) hydrofluoric acid 1. Know symbol ↔ name & find position in P.T. quickly for HI (aq) hydroiodic acid 5. Binary Ionic Cmpds first 36 elements plus A. main group elements Sr Cs Ba Pd Ag Cd Sn Sb Pt Pb Bi Au Hg I Xe U • cation, anion (…ide) • determine charge on ions (group in P.T.) • smallest whole number ratio, balance for electroneutrality = “crossover method” 2. Diatomic/ Multiatomic Elements in their “standard states”: “ Cl i f Br o h n “ → Cl2, I2, F2, Br2, O2, H2, N2 also S8 , P4 CaO calcium oxide beryllium fluoride BeF2 SrI2 strontium iodide magnesium nitride Mg3N2 K2S potassium sulfide barium sulfide BaS 3. Binary Covalent Cmpds ( “nonmetal + nonmetal”) • less electronegative element first • more electronegative element second (ending …ide) • use Latin/Greek prefixes ((mono), di, tri, tetra, penta, hexa, hepta, octa, B. transition metals, also Sn, Pb Indicate charge on cation w/ Roman numeral nona, deca) TiCl4 titanium(IV) chloride chromium(II) chloride CrCl2 NiS nickel(II) sulfide copper(I) oxide Cu2O Fe2S3 iron(III) sulfide iron(III) sulfide Fe2S3 CO carbon monoxide SF6 sulfur hexafluoride P4O10 tetraphosphorus decaoxide 8-15 8-16 8. Acidic Anions 6. Standard Oxoacids & Derived Anions (incomplete loss of H from acid): hydrogen ….ate, ite, … HSO4– hydrogen sulfate sodium hydrogen sulfate NaHSO4 H2CO3 carbonic acid CO32– carbonate HNO3 nitric acid NO3– nitrate NaHSO3 sodium hydrogen sulfite dihydrogen phosphate anion H2PO4 – H3PO4 phosphoric acid PO43– phosphate K2HPO3 potassium hydrogen phosphite H2SO4 sulfuric acid SO42– sulfate HClO3 chloric acid ClO3– chlorate HBrO3 bromic acid BrO3– bromate HIO3 IO3– sodium hydrogen carbonate NaHCO3 9. Hydrates: indicate # of H2O by Greek/Latin letters CuSO4 • 5H2O copper(II) sulfate pentahydrate Na2SO4• 10H2O sodium sulfate decahydrate 10. Special Cases iodic acid iodate 7. More or Less O than “standard” acid/anion 2 less O : hypo…..ous acid; 1 less O : …..ous acid; 1 more O: per…..ic acid; hypo…..ite …..ite per…..ate HClO2 chlorous acid potassium perchlorate KClO4 HIO4 perchloric acid sodium nitrite NaNO2 HNO2 nitrous acid sodium sulfite Na2SO3 KBrO potassium hypobromite ammonium phosphite (NH4)3PO3 OH – NH3 ammonia + NH4 ammonium CN H2O2 hydrogen peroxide C2H3O2– acetate cyanide MnO4 – H2O water HC2H3O2 (= CH3CO2H) hydroxide – acetic acid 2– CrO4 permanganate chromate Cr2O72– dichromate 8-17 8-18 Derivation of Avogadro’s Number, NA Chem. Formulas Ex. hydrogen peroxide • empirical The following are definitions: (arbitrary, but optimal selection) • (relative) atomic mass of C-12 = 12 u (exact) (HO) smallest whole number ratio of atoms • 1 mol of C-12 = 12 g C-12 (exact) • molar mass (MM) of C-12 = 12 g/mol • molecular gives the number To find the number of atoms per mol (NA), H2O2 of each atom in molecule we need to determine the absolute mass (m) of a C-12 atom; • structural (this can be done by mass spectrometry, X-ray crystalography ...) shows all bonds, H–O–O–H m of C-12 (by experiment) = 1.993 x 10–23 g may include geometric info, H ∴ O O MM 12 g/mol NA = m = 1.993x10–23g = 6.022 x 1023 mol–1 H 8-19 8-20 Mole Concept Mass Moles 1 mol = 6.02 x 1023 “things” Use MM as CF (conversion factor) NA = Avogadro’s #; units: mol–1 Practice can refer to # of moles in 89.2 g NaF ? atoms molecules formula units ions electrons photons electronic transitions molecular conversions (“dogs” ?) Molar Mass (MM) mass of 1 mol of “particles”; g units: mol to determine, see Pet., p. 72 W G MM = 42.0 g/mol 1 mol 89.2 g x 42.0 g = 2.12 mol 8-21 8-22 balancing ... Balancing Chem. Equations Ex. • # of atoms of each kind same on both sides __ PCl5 + __ H2O • total charges same on both sides • “systematic trial & error method” P: 1 - start with an element in most complicated cmpd __ H3PO4 + __ HCl 1 Cl: (1 x 5) - balance O, H near end 5 O: 4 (4) - do elements last H: - multiply/ divide to get simplest whole number coefficients (4 x 2) 1 PCl5 + 4 H2O (3 x 1) (5 x 1) 1 H3PO4 + 5 HCl 8-23 8-24 Stoichiometric Calculations W G MM mass G moles G • Check how much Product each Reactant can make MM moles W Limiting Reactant (L.R.) mass W • Reactant that makes least Product = L.R. W G = M.R. (molar ratio) of W/G Yield Ex. In the synthesis of NH3, how many g of N2 are needed to convert 35.2 g H2? W G N2 + 3 H2 → 2 NH3 1mol H2 1mol N2 28.0g N2 35.2 g H2 x 2.02g H x 3mol N x 1mol N 2 2 2 = 163 g N2 actual: obtained in experiment ( g or mol) theoretical: calculated by stoichiometry ( g or mol) (take into account L.R.) % yield: actual theoretical x 100% 8-25 % Composition from Chem. Formula 8-26 Determination of Empirical Formula (from “mass data”, or “combustion data”, or ...) Ex. Percentage of U in “Yellow Cake” ? convert to mole data for each element, then find simplest whole number ratio “yellow cake” = U3O8 Ex. A cmpd contains 74.1% C, 8.64% H, 17.3% N. Empirical formula ? Imaginary Reaction: U3O8 + ... → 3 U + ... Base on 100g cmpd: base on 100g compound mass (g) divide by MM moles (mol) divide by “lowest moles” nearest whole numbers 1mol U3O8 3mol U 238g U 100g U3O8 x 842g U O x 1mol U O x 1mol U 3 8 3 8 = 84.8 g U C 74.1 12.01 6.17 4.99 5 H 8.64 1.008 8.57 6.93 7 This corresponds to 84.8% U in “yellow cake”, since we based our calculation on 100 g. N 17.3 14.01 1.24 1.00 1 ∴ Empirical Formula: (C5H7N) 8-27 8-28 Molecular Formula Miscellaneous Need MM data (from experiment) Density Divide usually: MM of cmpd by MM of “empirical formula” solids, liquids : g/mL gases: g/L (can be used as C.F.’s) to get multiplication factor Ex. Empirical formula = (CH); MM ≈ 80 g/mol Molecular Formula? Concentration MM of “empirical formula”: 13.0 g/mol usually: mol/L (“M”) Divide: 80 g/mol 13 g/mol = 6.15 Dilution close to 6; multiply emprical formula by 6 a.) c1V1 = c2V2 , or Molecular formula: (CH) x 6 = C6H6 V1 V3 b.) c1 x V x V x .... = cfinal 2 4 8-29 CB I Summary • Distinguish between ionic and covalent bonding • Systematic Nomenclature Review: distiguish 8 different cases; convert name↔ formula • Systematic Stoichiometry Review mole concept balancing chem. equations mass relations in chem. rxns chem. compostion from formula empirical formula from composition or reaction data molecular formula from molecular mass and empirical formula