1Lecture 4: C1403 Monday, September 19, 2005Stoichiometry : Mass relationships involvedin compositions of compounds and inbalanced chemical equations.Converting mass of substances to moles(numbers of atoms and molecules) and molesto mass.2From the mass of 22.4 L of gases to atomic and molecularmolar masses.22.4 L determined as containing a mole of a gas.Compound (22.4 L) Mass % of O Mass of OWater 18 g 89% O 16 g O/moleCarbon dioxide 44 g 73% O 32 g O/moleSulfur trioxide 80 g 60% O 48 g O/moleOxygen 32 g 100% O 32 g O/moleData consistent with atomic molar mass of H = 1 & O = 16.Creation of a ranking of atomic masses throughAvogadro’s hypothesis and the mass of volumes of gases.3Mole equivalents:2 H2 = 1 O2 = 2 H2OAtom equivalents:4 H + 2 O = 4 H + 2 OMass to mole to mole to mass conversion4 g H2 = 2 mol H2 = 1 mol O2 = 32 g O24 g H2 = 2 mol H2 = 2 mol H2O = 36 g H2OEquation: 2 H2 + O2 = 2 H2O(constitutional structure)Molecular compositionsBalanced equations4Laboratoryamounts: massesChemical amounts:numbers of atomsor molecules. Equalamounts meansequal numbers ofatoms5Equal masses: excessof lighter atom inreactionA + B = ABA is limiting reactantEqual number:No excess ofeither A or B inreactionA + B = ABA BLimiting reactant depends on number not on mass.6Chapter 3 Chemical Periodicity and the Formation of SimpleCompounds. Lewis structures of molecules.Learning goals:Periodic Table(3.1) The characteristics of groups of the 8 representativegroups (I-VIII) of elements.(3.2) The relationships among the elements in the columns and rows of the Periodic Table.(3.2) Periodic Properties. Electronegativity.Lewis structures(3.3) Lewis dot electronic structures of atoms.(3.4, 3.5) Lewis dot-line constitutional structures of molecules. How atoms are connected.(3.7) Predicting the dipole moments and the configuration (3D) structure of molecules from Lewis structures.7(3.2) The Periodic TableClassical example of the building of a paradigm: Repeated patternsof similarity in the composition of binary compounds triggered asearch for order and organization of the elements in terms ofobservable properties.First organization of the periodic: By atomic mass.Periodicity of properties appeared as an arrangement by mass.About 1870 Mendeleev (Russia) and Meyer (Germany) proposed theinitial forms of the periodic table.Mendeleev dared to propose that deviations from periodicity weredue to either incorrect atomic weights or undiscoveredelements. He predicted the properties of six undiscoveredelements. Mendeleev’s paradigm wins (for a while)!8(3.1) Groups of Elements in the Periodic TableEight Groups (the 7 groups of representative elements andthe group of noble gases):I. Alkali metals: (H), Li, Na, K, Rb, CsII. Alkali earth metals: Be, Al, Ca, Sr, Ba, RaIII.Boron family: B, Al, Ga, In, TlIV. Carbon family: C, Si, Ge, Sn, PbV. Nitrogen family: N, P, As, Sb, BiVI. Chalcogens O, S, Se, Te, PoVII.Halogens F, Cl, Br, I, AtVIII. Noble gases: (He), Ne, Ar, Kr, Xe, RnRepresentative metals (I and II) and non-metals (VI and VII).9Group I (The alkali metals): Li, Na, K, Rb, Cs10Most of the elements in the periodic table are metals11Group VI (The chalcogens): O (oxygen), S (sulfur), Ge (germanium), Sn (tin)12Halogens (elemental forms)Group VII (The halogens): F (not shown), Cl (gas), Br (liquid), I (solid)13Br2 (non-metal) + Al (metal) Al2Br6 (AlBr3)What is the basis of chemical reactivity?14. Grouping elements by similarities. Science is an exercise in collecting data,detecting similarities in the data and in determining the source of thesimilarities at an atomic (microscopic) level.Many elements form binary compounds with H. Since H is the “simplest”element (smallest atomic mass), it is natural to consider the properties ofthe compounds formed between elements, X, and H. These binarycompounds, XHn, are called hydrides.Exemplars: CH4, NH3, OH2, FH (XHn n = 4, 3, 2, 1, respectively)Group binary hydrides of that bind the same number of H.Examples of grouping of hydrides of elements:n = 4 CH4, SiH4, GeH4n = 3 NH3, PH3, AsH3n = 2 OH2, SH2, SeH2n = 1 FH, ClH. BrH15Clear cut grouping of metals (Groups I and II) forming binarycompounds with non-metals (Groups VI and VII)Alkali metals, X: Li, Na, K, Rb, CsX2O Li2O, Na2O, K2O, Rb2O, Cs2OXCl LiCl, NaCl, KCl, RbCl, CsClAlkali earth metals, X: Be, Mg, Ca, Sr, BaXO BeO, MgO, CaO, SrO, BaOXCl2BeCl2, MgCl2, CaCl2, SrCl2, BaCl2Chalcogens, X: O, S, Se, TeNa2X Na2O, Na2S, Na2Se, Na2TeCaX CaO, CaS, CaSe, CaTeHalogens, X: F, Cl, Br, ILiX LiF, LiCl, LiBr, LiICaX2CaF2, CaCl2, CaBr2, CaI216Organize Elements by Stable Oxides,Hydrides, HalidesXeI-HITeO42-H2TeSbOSbCl3SnO2SnCl4In2O3InCl3SrOSrCl2Rb2ORbClKrBr -HBrSeO42-H2SeAsOAsCl3GeO2GeCl4Ga2O3GaCl3CaOCaCl2K2OKClArCl-HClSO42-H2SPOPCl3SiO2SiCl4Al2O3AlCl3MgOMgCl2Na2ONaClNeF-HF[O]H2ONONCl3CO2CCl4B2O3BCl3BeOBeCl2Li2OLiCl I II III IV V VI VII VIII17(3.2) The Periodic Table(1) The elements can be arranged in groups (columns) of elementsthat possess related chemical and physical properties.(2) The elements can be arranged in periods (rows) of elementsthat possess progressively different physical and chemicalproperties.(3) Original Paradigm: The chemical and physical properties of theelement are periodic functions of their atomic masses.(4) Modern Paradigm: The chemical and physical properties of theelements are periodic functions of the atomic number (numberof protons in the nucleus = number of electrons in the neutralatom).18Dmitri MendeleevOrganization of the elements by relative atomicmass and periodic properties.19Modern basis for the periodic table: the numberof protons in the atomic nucleus (atomic number)198Au20An alphabetical arrangement of the elements (information)21A spiral periodic table22Same information (atomic numbers and atomic masses),provided with a constitutional (connected) structure =knowledge (connecting properties and function)23Substructure of the periodic table by properties24The periodic table by “sizes” (atomic radius ) of atoms25(3.2) Periodic Properties. Electronegativity.Two critical properties determining chemicalreactivity are the energies involved in adding orremoving an electron from an atom.Electronegativity is measure of the power of anatom to attract electrons to itself.Metals: Low tendency to attract electrons, hightendency to release electrons.Non-metals: High tendency to attract electrons, lowtendency to release electrons.26B has a bigger “pull” on the electrons in