chm2045ch3 - M ol ecul es, I ons, & Compounds Chapter 3...

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Unformatted text preview: M ol ecul es, I ons, & Compounds Chapter 3 NaCl, salt Ethanol, C2H6O Buckyball, C60 Chapter Goals Interpret, predict, and write formulas for ionic and molecular compounds Nomenclature Properties of ionic compounds. More on molar mass. Percent composition and derivation of formulas from experimental data. Molecule an assembly of 2 or more atoms (mostly of non-metals) bound together in a particular ratio and a particular manner Elements that exist as molecules Atoms of most of the nonmetals form discrete molecules, except for the noble gases: H2, O2, N2, F2, Cl2, Br2, I2 Some elements can exist in more than one form of molecule; the different forms are called allotropes. Examples are: Diamond, graphite, and buckyballs for carbon. O2 and O3 (ozone) for oxygen. ChemNow 3.2 ELEM EN T S T H AT EXI ST AS M OLECU LES Allotropes of C ELEM EN T S T H AT EXI ST AS POLYAT OM I C M OLECU LES White P4 and polymeric red phosphorus Sulfur: crownshaped rings of S8 molecules Molecular compounds Are made of non-metals H2O, CO2, NH3, HNO3, ethanol, CH3CH2OH, are examples among thousands - show how atoms are grouped together ChemNow 3.3 Molecular compounds: Formulas NAME MOLECULAR FORMULA CONDENSED FORMULA STRUCTURAL FORMULA Ethanol C2H6O CH3CH2OH H H | | HC COH | | H H H H | | HC O CH | | H H Dimethyl ether C2H6O CH3OCH3 Ethanol and dimethyl ether are said to be structural isomers. Ionic Compounds Ion charged particle [atom, Cl-, or group of atoms, ClO4-) cation: + charge (Na+) anion: charge (Cl-) Ionic compounds consist of positive and negative ions, mostly a metal and a non-metal, respectively. have attractions called ionic bonds between positively (cations) and negatively charged ions (anions). have high melting and boiling points. are solid at room temperature. Charge Balance NaCl, sodium chloride Monatomic Cations Group 1 (1A) metals of group lose one electron to produce a mono-positive ion Na 11 p+ 11 e- Na+ + e11 p+ 10 e- Monatomic Cations Metal atoms of group 2A lose two electrons to produce di-positive ions Monatomic Anions Nonmetals often gain one or more electrons and form ions having a negative charge equal to 8 minus the group number of the element: Charges of Representative Elements Monatomic Cations Transition metals (B-group elements) form a variety of cations: Group Atom Electrons loss Resulting cation 7B Mn 2 Mn2+ 8B Fe 2 Fe2+ 8B Fe 3 Fe3+ 1B Cu 1 Cu+ 1B Cu 2 Cu2+ 2B Zn 2 Zn2+ 2B Cd 2 Cd2+ Transition Metals form Positive Ions Most transition metals and Group 4A metals form 2 or more positive ions. Zn, Ag, and Cd form only one ion. Names of Some Common Ions Main group metals element name only Nonmetal: change the last part of the name to ide Naming Cations transition metals and In, Sn, Tl, Pb, Bi new system: element name (charge in Roman numerals) eg. Mn2+ manganese(II) Mn3+ manganese(III) Cr2+ chromium(II) Cr3+ chromium(III) Fe2+ iron(II) Fe3+ iron(III) Exceptions: when only one cation + 2+ 2+ Previous system Latin name plus suffix suffix = -ic for higher charge, -ous for lower charge eg. Cu+ copper(I) cuprous ion Cu2+ copper(II) cupric ion Co2+ cobalt(II) cobaltous ion Co3+ cobalt(III) cobaltic ion Fe2+ iron(II) ferrous ion Fe3+ iron(III) ferric ion Polyatomic Ions A polyatomic ion is a group of atoms. has an overall positive or negative charge. Polyatomic Ions (learn) Some examples of polyatomic ions are NH4+ ammonium hydronium OH- hydroxide H3O+ N3- CN- azide cyanide C2O42- NO2- PO33- oxalate CO32- carbonate CH3CO2- NO3- acetate nitrate nitrite phosphite PO43- phosphate Hydrogenated Polyatomic Ions HCO3- HSO4- HSO3- hydrogen carbonate (bicarbonate) hydrogen sulfate (bisulfate) hydrogen sulfite (bisulfite) HPO42- hydrogen phosphate H2PO4- dihydrogen phosphate HS- hydrogen sulfide (from Oxyanions that end in -ate Group III A BO33 borate Group IV A CO32 carbonate SiO32 silicate Group VA NO3 nitrate PO43 phosphate AsO43 arsenate SO42 sulfate SeO42 TeO42 tellurate ClO3 chlorate BrO3 IO3 iodate Group VI A Group VII A selenate bromate Other oxyanions: From ions ending in -ate, those with different nos of O atoms are named with the following prefixes and suffixes 2 oxygen less 1 oxygen less than the "ate" than the "ate" ion is ion is hypo__ite ___ite 1 oxygen more than "ate" ion is per__ate BrO2 BrO4 bromite perbromate Halogens; P; As ClO4 perchlorate ClO3 chlorate ClO2 chlorite ClO hypochlorite The same with other halogens (except for F) IO4 periodate IO3 iodate IO2 iodite P and As PO53 PO43 PO33 PO23 AsO53 AsO43 AsO33 AsO23 perphosphate phosphate phosphite hypophosphite perarsenate arsenate arsenite hypoarsenite combination of ions in simplest whole number ratio to be electrically neutral (the simplest unit of an ionic compound) consists of positively and negatively charged ions. is neutral. has charge balance. total positive charge = total negative charge The symbol of the metal is written first followed by the symbol of the nonmetal. Formula Unit Naming Ionic Compounds with Two Elements To name a compound that contains two elements, identify the cation and anion. name the cation first followed by the name of the anion. Examples, name each below KBr K+ potassium Br bromide potassium bromide AlF3 Al3+ aluminum F fluoride aluminum fluoride Sr3P2 Sr2+ -6 strontium P3 phosphide Sr 3 (+2) = +6 P 2 (-3) = strontium phosphide CuCl2 Cl chloride Cu2+ copper(II) cupric Cu 1 (+2) = +2 Cl 2 (-1) = -2 copper(II) chloride, or cupric chloride CuCl: copper(I) chloride WF6 F -6 fluoride W6+ tungsten(VI) W 1 (+6) = +6 F 6 (-1) = tungsten(VI) fluoride Naming Ionic Compounds with Polyatomic Ions The positive ion is named first followed by the name of the polyatomic ion. NaNO3 K SO4 Fe(HCO3)3 (NH ) PO3 sodium nitrate potassium sulfate iron(III) bicarbonate or iron(III) hydrogen carbonate ammonium phosphite Writing Formulas with Polyatomic Ions The formula of an ionic compound containing a polyatomic ion must have a charge balance that equals zero (0). Na+ and NO NaNO with two or more polyatomic ions has the polyatomic ions in parentheses. Mg2+ and 2NO Mg(NO ) subscript 2 for charge balance Aluminum sulfate 2Al3+ and 3SO42- Al2(SO ) calcium phosphide Ca Ca2+ P For neutrality we need P3 3 Ca2+ and 2 P3 Ca3P2 that is, +6 6 = 0 niobium(IV) sulfite Nb4+ In order to have the same SO32 total + and charge, we need one Nb ion and two SO , that is 1 (+4) + 2 (2) = 4 4 =0 (neutrality) Nb(SO3)2 El ectr osta ti c For ces The oppositely charged ions in ionic compounds are attracted to one another by ELECT ROSTAT I C FORCES. These forces are governed by COU LOM B'S L AW. El ectr osta ti c For ces COU LOM B'S L AW As ion charge increases, the attractive force increases. As the distance between ions (d) increases, the attractive force decreases. T hi s i dea i s i mpor ta nt a nd wi l l come up ma ny ti mes i n futur e di scussi ons! Q cQ a F 2 d + Product of charges 1 2 4 6 strongest force NaCl 2 Na 2+ Cl CaCl CaS 3 2 Al S Ca2+ Ca3+ Al Cl 2 S 2 S Q cQ a F 2 d + d + d Na d NaF has the strongest force and NaI the weakest F Na Cl d + + Na I Na Br Naming Acids H+ is only cation Binary Acids hydrogen bonded to one other element hydro-anion-ic acid Examples HCl H+ and Cl anion is chloride hydro-chlor-ic acid hydrochloric acid H2S hydrosulfuric acid H3P hydrophosphoric acid H2Te hydrotelluric acid Oxoacids hydrogen, oxygen, and another element anion-suffix acid anion suffix: -ate -ic, -ite -ous acid Examples PO43 phosphate H PO phosphoric acid H SO sulfuric acid SO42 sulfate PO33 phosphite SO32 sulfite If more than two oxoacids, that with less O than the ous will be hypo ous; that with more O than the ic will be per ic. BrO hypobromite BrO2 bromite Molecular Compounds contain only nonmetals bound by covalent bonds methane, CH4 Covalent bonds form when atoms share electrons to complete octets. There are no ions!!! Naming Molecular (Covalent) Compounds To name covalent compounds STEP 1: Name the first nonmetal as an element. STEP 2: Name the second nonmetal with an ide ending. STEP 3: Use prefixes to indicate the number of atoms (subscript) of each element. Prefixes Used in Naming Covalent Compounds # of Atoms Prefix 1 Mono 2 Di 3 Tri 4 Tetra 5 Penta 6 Hexa 7 Hepta 8 Octa 9 Nona 10 Deca Exception prefix mono- is omitted from name of first element eg. CO2 carbon dioxide, not monocarbon dioxide Example What is the name of SO3? 1. The first nonmetal is S sulfur. 2. The second nonmetal is O named oxide. 1. The subscript 3 of O is shown as the prefix tri. SO3 sulfur trioxide The subscript 1 (for S) or mono is understood (not used for first element!!) Example P2O5 phosphorus Diphosphorus (two P atoms) oxygen oxide Pentoxide(5 O atoms) diphosphorus pentoxide P3Br6 phosphorus triphosphorus bromine bromide hexabromide triphosphorus hexabromide Learning Check Write the name of each molecular (covalent) compound. CO CO2 PCl3 CCl4 N2O _____________________ _____________________ _____________________ _____________________ _____________________ Learning Check Write the correct formula for each of the following. A. phosphorus pentachloride B. dinitrogen trioxide C. sulfur hexafluoride Common Names H2O PH3 CaCO3 CaO Ca(OH)2 CH4 NaCl water phosphine limestone lime slaked lime methane table salt N2O NaHCO3 Na2CO310H2O MgSO47H2O Mg(OH)2 Ca(SO4)2H2O laughing gas baking soda washing soda epsom salt milk of magnesia gypsum Hydrogen belongs in group all its own generally considered a nonmetal forms both H+ and H in ionic compounds HCl (in aqueous solution) H and Cl NaH Chemical Formulas empirical formula indicates the elements present and their simplest, whole-number ratio in a compound molecular formula indicates elements present and the exact number of atoms of each in a unit of a compound structural formula a molecular formula that includes structural information Benzene structural formula H H C H C C C H C H C H molecular formula C6H6 empirical formula CH (after dividing by 6) Dimethylether Dimethyl ether C 2H 6O CH3OCH3 H H | | HC O CH | | H H condensed formula H3COCH3 molecular formula C2H6O empirical formula C2H6O Calcium Chloride (ionic) structural formula molecular formula formula unit empirical formula none none (it is ionic) CaCl2 CaCl2 Other examples NAME butanoic acid C2H4O diboron hexahydride BH3 Molecular Empirical formula formula C 4H 8 O 2 C 4H 8 O 2 2 B2H6 2 2 B2H6 2 2 sodium dithionite Na2S2O4 NaSO2 Molar Mass of a Compound is the mass (g) of one mole (6.022 x 10 ) of formula units for ionic compounds molecules for molecular compounds The molar mass of a compound is the sum of the molar masses of the elements in the formula. molecular/formula weight = amu/molecule molar mass = g/mol of molecules Molar Mass of a Compound Example: Calculate the molar mass of CaCl2 (ionic) Element Number of Moles Atomic Mass Total Mass Ca 1 40.1 g/mole 40.1 g Cl 2 35.5 g/mole 71.0 g 2 Molar Mass (M), Avogadro's number, and atoms of elements 1 mole = 6.022 x 10 particles = molar mass (g) 6 12 6 23 Molar Mass and Avogadro's number The mass (in grams) of a single molecule The molar mass of water, H2O, is 2 x 1.008 + 16.00 = 18.02 g/mol (about 18 mL) Does a water molecule have a mass of 18.02 g? No, it doesn't. 18.02 g (the molar mass) 1 mol H2O -------------------- 6.022 x 1023 H2O molecules by diving, we get 2.99x10 g per H O molecule What is the mass of 12.0 million benzene (C6H6) molecules? Molar mass = (6 mol C)(12.01 g/mol C) + (6 mol H)(1.008 g/mol H) = 78.11 g/mol C6H6 12.0 million= 12,000,000 = 1.20 x 107 molecules 1.20 x 10 molec.x 1 mol x 78.11 g 6.022 x 10 molecules 1 mol 78.11 g = 1.99 x 1017 mol C6H6 = mol C6H6 1.56 x 1015 g C6H6 Consider 4.49 g Ca (PO ) . Its formula weight FW = many mol 2x(30.97 + 4x16.00)=310.18 g/mol How 3x40.08 + of Ca3(PO4)2 is this? 1 mol 4.49 g x = 0.0145 moles Ca3(PO4)2 310.18g How many mol of Ca2+ ions does this contain? 3 moles Ca2+ 0.0145 mol Ca3(PO4)2 x = 0.0435 mol Ca2+ 1 mol Ca3(PO4)2 How many atoms of Ca2+ ions are there? 0.0435 mol Ca2+ x = 2.61x1022 ions 6.022 x10 Ca2+ Consider 4.49 g Ca (PO ) How many mol of P does that amount of Ca3(PO4)2 FW = 310.18 g/mol contain? 2 moles P 0.0145 mol Ca3(PO4)2 x = 0.0290 mol P 1 mol Ca3(PO4)2 How many mol of O does that amount contain? 8 moles O 0.0145 mol Ca3(PO4)2 x = 0.116 mol O 1 mol Ca3(PO4)2 How many grams of O is that? 16.0 g O 0.116 mol O x = 1.86 g O 1 mol O Consider 4.49 g Ca (PO ) How many phosphate ions does that amount of FW = 310.18 g/mol Ca3(PO4)2 contain? First we calculate how many moles of phosphate 2 moles PO43- 0.0145 mol Ca3(PO4)2 x = 0.0290 mol PO43- 1 mol Ca3(PO4)2 6.02 x 1023 PO43- 0.0290 mol PO43- x = 1.75 x 1022 What mass of C H O is required to Molar mass = 72.10 g/mol supply 1.43 x 10 C atoms? 1 mol C atoms 1 mol C4H8O Empirical Formula from Analysis See next example A compound was found to be 40.92 % C, 4.58 % H, and 54.50 % O by mass. Determine its empirical formula. CxHyOz x, y, and z are the simplest whole number ratios of atoms in compound. Assume exactly 100 g of compound then 40.92 g C, 4.58 g H, and 54.50 g O are contained in those 100 g Firstly, calculate the number of moles of C, H, and O in that amount of compound... next 1 mole C 40.92 g C x = 3.407 moles C 12.01 g C 1 mole H 4.58 g H x = 4.54 moles H 1.008 g H 1 mole O 54.50 g O x = 3.406 moles O 16.00 g O C3.407H4.54O3.406 C3.407H4.54O3.406 3.406 3.406 3.406 Now, divide all # by the smallest The result is C1.0H1.33O1.0 Empirical formula is 3 4 3 Finally, 1.33 x 3 = 4 Determine the empirical formula of a compound that is 36.4% Mn, 21.2% S, and 42.4% O by mass. assuming exactly 100 g compound 1 mole Mn 36.4 g Mn x = 0.663 moles Mn 54.9 g Mn 1 mole S 21.2 g S x = 0.660 moles S 32.1 g S 1 mole O 42.4 g O x = 2.65 moles O 16.0 g O Mn0.663S0.660O2.65 Mn1.0S1.0O4.02 0.660 0.660 0.660 The result is 4 molecular formula = n x (empirical formula) n = whole number n = weight of the empirical formula molar mass (or formula weight) Example: benzene, molecular formula: C6H6 empirical formula: CH n=6 6 x (CH) = C6H6 Example: A 4.99 g sample of a compound was found to contain 1.52 g N and oxygen. Determine its empirical and molecular formula if its MW is 92.04 determine empirical formula g O = 4.99 -1.52 1 mol N = 3.47 g 1.52 g N = 0.108 mol N 14.01 g N 1 mol O 3.47 g O = = 0.217 mol O 16.00 g O N0.108O0.217 0.108 0.108 NO2 determine molecular formula empirical formula NO2 empirical weight = 14.01+ 2 16.00 = 46.01 molecular weight = 92.04 (given in previous slide) 92.04 n = = 2 46.01 Molecular formula = 2 x (emp. form.) = 2(NO2) molecular formula = N2O4 A compound was found to contain only B and H. Analysis of an 8.247 g sample indicated that it contained 1.803 g H and had a MW of ~30. Determine its molecular formula and its MW to 4 SF. determine empirical formula total mass = g B + g H 8.247 g = g B + 1.803 g H g B = 8.247 g compound -1.803 g H =6.444 g 1 mol B 6.444 g B = 0.5961 mol of boron 10.811 g B 1 mol H 1.803 g H = 1.789 mol H 1.008 g H B0.5961 H1.789 BH3 is the Empirical formula 0.5961 0.5961 determine molecular formula MW 30 n = = 2 emp. wt. 13.83 mol. form. = 2(BH3) = B2H6 Hydrates compounds that contain intact H2O eg. CaSO42H2O compound name prefix-hydrate (prefix indicates number of H2O molecules) calcium sulfate dihydrate LiCl8H2O lithium chloride octahydrate tungsten(VI) sulfate heptahydrate W6+ SO42 W(SO4)37H2O Hydrated nickel(II) chloride is a beautiful green color, crystalline compound. When heated strongly, the compound is dehydrated. If 0.235 g of NiCl2xH2O gives 0.128 g of NiCl2 on heating, what is the value of x? g of NiCl2xH2O = g NiCl2 + g H2O Then, hydrated dehydrated g H2O = 0.235 g 0.128 g = 0.107 g 1 mol NiCl2 0.128 g NiCl2 x = 0.000987 moles NiCl2 129.7 g NiCl2 2 2 1 mol H2O 0.107 g H2O x = 18.0 g H2O 0.00594 moles H2O Percent Composition The percent of the total mass of a substance represented by each element within that substance In other words, how many grams of every element are in 100 g of the compound Determine the % composition of aluminum bromite Al3+ BrO2 Al(BrO2)3 Al Br O FW = 26.982 + 3 x(79.904 + 2 x 16.000) = 362.68 g/mol g Al % Al = x 100 g compound 26.982 g % Al = x 100 = 7.440 % 362.68 g g Br % Br = x 100 g compound 3 x 79.904 g % Br = x 100 = 66.095 % 362.68 g % O = 100% 7.440% 66.095 = 26.465% ...
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This note was uploaded on 08/24/2008 for the course CHM 2045 taught by Professor Geiger during the Summer '08 term at University of Central Florida.

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