Chem 103, Section F0FUnit III - Combining Atoms to Make Compounds, Part I: Ionic CompoundsLecture 10•The atomic properties and chemical bonds•Ionic bonding.•Naming ionic compounds and representing them with chemical formulasLecture 10 - Chemical Bonding and Ionic Compounds•Reading in Silberberg-Chapter 9, Section 1 Atomic Properties and Chemical Bonds-Chapter 2, Section 7 Compounds: Introduction to Bonding-Chapter 9, Section 2 The Ionic Bonding Model-Chapter 2, Section 8 (pp. 64-70) Ionic Compounds: Formulas and Names2Lecture 10 - IntroductionWe will look first at chemical bonding•With a focus on ionic bonds and ionic compounds.We will then look at the source of energy needed to form ionic compounds.We will also look into how chemical formulas are used to represent compounds•And the systematic way of naming ionic compounds.3Lecture 10 - Atomic Properties and Chemical BondsNearly all naturally occurring substances consist of atoms or ions bonded to other atoms or ions.•There are very few elements that occur uncombined in nature•Most exist combined with other elements to form compounds.4Lecture 10 - Atomic Properties and Chemical BondsChemical bonding allows atoms to lower their energy.Types of chemical bonding include:•Ionic bonding (metals with nonmetals)•Covalent bonding (nonmetals with nonmetals)•Metallic bonding (metals with metals)5Lecture 10 - Atomic Properties and Chemical BondsIonic bonding•Occurs when metal atoms transfer valance electrons to nonmetal atoms.-The resulting attraction of the opposing charges leads to the formation of ionic solids.6Lecture 10 - Atomic Properties and Chemical BondsIonic bonding•For monatomic ions-The metals lose and nonmetals gain that number of electrons that will make them isolectronic with the nearest noble gas.7Lecture 10 - QuestionWhat monatomic ions do barium (Z = 56) and sulfur (Z = 16) form?8Lecture 10 - Atomic Properties and Chemical BondsCovalent bonding•Occurs most commonly between nonmetals.-In covalent molecules, the atoms share pairs of valence electrons.9Lecture 10 - Atomic Properties and Chemical BondsCovalent bonding•We will come back later to look a covalent molecules•However, when considering ionic compounds we will encounter polyatomic ions-These are a group of atoms that are covalently bonded to one another, but have a net positive or negative charge.!They therefore also participate in ionic bonding.10Carbonate Ion (CO32-COO O2-Lecture 10 - Atomic Properties and Chemical BondsMetallic bonding•Occurs when many metal atoms pool their valence electrons.-This pool of electrons holds the metal atoms together.11Lecture 10 - QuestionAre molecules of MgBr2 present in a sample of MgBr2?Explain12Lecture 10 - QuestionAre ions present in a sample of P4O6?Explain13Lecture 10 - QuestionPredict the type of bonding, ionic, covalent, or metallic, you would predict for each of the following:A) CsF(s)B) H2S(g)C) N2O(g)D) CaO(s)E) BrO2(g)F) Cr(s)14Lecture 10 - Atomic Properties and Chemical BondsLewis dot structures are used to represent the valence electrons for an atom•They are usefull for illustrating the formation of both ionic and covalent compounds.15Lecture 10 - Atomic Properties and Chemical BondsLewis dot structures are used to represent the valence electrons for an atom•They are useful for illustrating the formation of both ionic and covalent bonded molecules.16Forming lithium fluoride from lithium metal and fluorine gasLecture 10 - QuestionDraw a Lewis electron-dot symbol forA) BaB) KrC) SeD) PE) Rb17Lecture 10 - QuestionGive the group number an general elecron configuration of an element with each electron-dot symbolA) B) C) D)18XXXXLecture 10 - QuestionIdentify the main group to which X belongs in each ionic compound formula:A) XPO4B) MgX2C) Na3XD) Al2X3Lecture 10 - Ionic BondingIon formation by itself requires energy•The negative Electron Affinities (EA’s) of the nonmetals are not sufficient to compensate for the positive Ionization Energies (IE’s) of the metals.20IE’s EA’sLecture 10 - Ionic BondingIon formation by itself requires energy•For the formation of lithium fluoride-IE1 (lithium) + EA1 (fluoride) = 520 - 328 = 192 kJ/mol21IE’s EA’sLecture 10 - Ionic BondingIon formation by itself requires energy•The required energy for forming ionic compounds comes from the lattice energy.-The lattice energy is the energy absorbed when an ionic solid separates into gaseous ions.!It is very large and is the major reason that ionic solids exist.-The lattice energy depends on ionic size and charge and can be calculated using Hess’s Law in the Born-Haber cycle.•Hess’s Law - the enthalpy or energy change of an overall process is the sum of the enthalpy or energy changes of its individual steps.22Lecture 10 - Ionic Bonding23Lecture 10 - Ionic Bonding24Ion formation by itself requires energy•The required energy for forming ionic compounds comes from the lattice energy.-The ionic interactions can be described by Coulomb’s law Eelectrostatic=charge A ! charge BdistanceLecture 10 - Ionic Bonding25The smaller the ions, the stronger the interaction.Lecture 10 - Ionic BondingThe ionic bonding model pictures oppositely charged ions held together by strong electrostatic interactions.•This model explains why ionic solids tend to fracture when struck.26As layer slip past on another,charge repulsion leads to a fractureLecture 10 - Ionic BondingThe ionic bonding model pictures oppositely charged ions held together by strong electrostatic interactions.•This model explains why they conduct electricity only when melted or dissolved.27Lecture 10 - Ionic BondingThe ionic bonding model pictures oppositely charged ions held together by strong electrostatic interactions.•Gaseous ion pairs require very high temperatures.28Lecture 10 - Chemical Formulas and Names for Ionic CompoundsChemical formulas describe•the simplest atom ratio(empirical formula)•the actual atom number (molecular formula)•The atom arrangement (structural formula) of one unit of a compound.29Type of BondingNameEmpiricalFormulaMolecular FormulaStructuralFormulaIonicMagnesiumChlorideMgCl2(formula unit)CovalentHydrogenPeroxideHOH2O2H-O-O-HLecture 10 - Chemical Formulas and Names for Ionic CompoundsIonic compounds are named by listing the cation first followed by the anion.•For metal cations that can have more than one charge state, Roman numerals are used to indicate the charge.•Monatomic anions add the -ide