Bonding and Molecular Structure: Fundamental ConceptsSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Chapter 9 1Bonding and Molecular Bonding and Molecular Structure: Fundamental Structure: Fundamental ConceptsConceptsChapter 9Chapter 9Chapter 9 2Valence ElectronsValence Electrons-The electrons involved in bonding are called valence electrons.-Valence electrons are found in the incomplete, outermost orbital shell of an atom.-We can represent the electrons as dots around the symbol for the element.-These pictorial representations are called Lewis Structures or Lewis Dot Structures.Chapter 9 3Lewis Symbols and the Octet RuleLewis Symbols and the Octet RuleChapter 9 4Chemical Bond FormationChemical Bond Formation-There are three types of chemical bondsIonic Bond - electrostatic attraction between ions of opposite charge (NaCl).Covalent Bond - sharing of electrons between two atoms (Cl2).Metallic Bond - sharing of electrons between several atoms (Ag).Chapter 9 5Ionic BondingIonic BondingConsider the reaction between sodium and chlorine:Na(s) + ½Cl2(g)  NaCl(s)Chapter 9 6Ionic BondingIonic BondingNa(s) + ½Cl2(g)  NaCl(s) H°f = -410.9 kJ-This reaction is very exothermic-Sodium loses an electron to become Na+ -Chlorine gains an electron to become Cl -Na+ has an Ne electron configuration and Cl has an Ar configurationChapter 9 7Ionic BondingIonic BondingEnergetics of Ionic Bond FormationEnergetics of Ionic Bond FormationLattice Energy (Hlattice) – The energy required to completely separate one mole of a solid ionic compound into its gaseous ions.Lattice energy depends on -the charge on the ions-the size of the ionsCoulomb’s equation:Q1, Q2 = charge on ionsk = 8.99 x 109 J-m/c2d = distance between ionsdQQkE21Chapter 9 8Covalent BondingCovalent BondingWhen similar atoms bond, they share pairs of electrons to each obtain an octet.Example a pair of electrons connect the two nuclei.Cl ClCl Cl +Chapter 9 9Covalent BondingCovalent BondingMultiple BondsMultiple Bonds-It is possible for more than one pair of electrons to be shared between two atoms (multiple bonds)-One shared pair of electrons - single bond (H2)-Two shared pairs of electrons - double bond (O2)-Three shared pairs of electrons - triple bond (N2).-Generally, bond distances decrease as we move from single through double to triple bonds.H HO ON NChapter 9 10Lewis Symbols and the Octet RuleLewis Symbols and the Octet RuleOctet rule – Atoms tend to gain, lose or share electrons until they are surrounded by eight valence electrons.Chapter 9 11Drawing Lewis StructuresDrawing Lewis Structures1) Draw a skeleton structure of the molecule or ion showing the arrangement of the atoms and the connect each atom to another with a single bond.2) Determine the total number of valence elections in the molecule or ion.3) Deduct 2 electrons for each single bond used in step 1.4) Distribute the rest of the electrons so that each atom (except H) has 8 electrons.-If you are “short” electrons, form multiple bonds-If you have “extra” electrons, one of the heavy atoms may be able to hold more that eight electrons.Chapter 9 12Drawing Lewis StructuresDrawing Lewis StructuresPCl3PClClClElement Number Electrons TotalP 1 5 5Cl 3 7 21Total Electrons 26Chapter 9 13Drawing Lewis StructuresDrawing Lewis StructuresPCl3PClClClElement Number Electrons TotalP 1 5 5Cl 3 7 21Total Electrons 26Electrons used 6Electrons remaining 20PClClClChapter 9 14Drawing Lewis StructuresDrawing Lewis StructuresIsoelectronic SpeciesIsoelectronic SpeciesMolecules or ions having the same number of valence electrons and the same Lewis structure.N NN OC O+Chapter 9 15Drawing Lewis StructuresDrawing Lewis StructuresResonance StructuresResonance Structures-Some molecules are not well described by Lewis Structures.Example: OzoneO1OO3O3OO1Chapter 9 16Drawing Lewis StructuresDrawing Lewis StructuresResonance StructuresResonance Structures- Experimentally, ozone has two identical bonds whereas the Lewis Structure requires one single and one double bond. OOOChapter 9 17Drawing Lewis StructuresDrawing Lewis StructuresResonance StructuresResonance Structures-Resonance structures are attempts to represent a real structure that is a mix between several extreme possibilities.-Each Lewis structure is call a Resonance FormResonance Form – Two or more Lewis structures having the same arrangements of atoms but a different arrangement of electronsChapter 9 18Drawing Lewis StructuresDrawing Lewis StructuresResonance StructuresResonance Structures-In ozone the resonance forms have one double and one single bond. -The actual structure of O3 is a combination (or average) of the individual forms called a resonance hybrid.OOOOOOChapter 9 19Exceptions to the Octet RuleExceptions to the Octet RuleThere are three classes of exceptions to the octet rule:-Molecules with an odd number of electrons-Molecules in which one atom has less than an octet-Molecules in which one atom has more than an octetChapter 9 20Exceptions to the Octet RuleExceptions to the Octet RuleOdd Number of ElectronsOdd Number of Electrons- there are few molecules which fit this categoryExamples. ClO2, NO, and NO2O N OChapter 9 21Exceptions to the Octet RuleExceptions to the Octet RuleLess than an OctetLess than an Octet-This refers to the central molecule-Typical for compounds of Groups 1A, 2A, and 3A.Examples: LiH, BeH2, BF3Be HHLi FBFFFChapter 9 22Exceptions to the Octet RuleExceptions to the Octet RuleMore than an OctetMore than an Octet-This starts for atoms in the 3rd period onwards.-This is due to vacant d orbitals which can hold the “extra” electrons.-Another factor is the size of the central atom, as they get bigger, it gets easier to place additional atoms around the central atom.Chapter 9 23Molecular ShapesMolecular ShapesLewis structures give atomic connectivity (which atoms are connected to which).Chapter 9 24Molecular ShapesMolecular ShapesMolecular Shapes are determined by:Bond Distance – Distance between the nuclei of two bonded atoms along a straight line.Bond Angle – The angle between any two bonds containing a common atom.Chapter 9 25Molecular