Chapter 9 Covalent Bonding: Orbitals AP*

AP Learning Objectives  LO 1.7 The student is able to describe the electron structure of the atom, using PES (photoelectron spectroscopy) data, ionization energy data, and/or Coulomb’s Law to construct explanations of how the energies of electrons within shells in atoms vary. (Sec 9.6)  LO 1.15 The student can justify the selection of a particular type of spectroscopy to measure properties associated with vibrational or electronic motions of molecules. (Sec 9.6)  LO 2.18 The student is able to rank and justify the ranking of bond polarity on the basis of the locations of the bonded atoms in the periodic table. (Sec 9.4)  LO 2.21 The student is able to use Lewis diagrams and VSEPR to predict the geometry of molecules, identify hybridization, and make predictions about polarity. (Sec 9.1, 9.6)

Section 9.1 Hybridization and the Localized Electron Model AP Learning Objectives, Margin Notes and References  Learning Objectives  LO 2.21 The student is able to use Lewis diagrams and VSEPR to predict the geometry of molecules, identify hybridization, and make predictions about polarity.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 4 Draw the Lewis structure for methane, CH 4.  What is the shape of a methane molecule? tetrahedral  What are the bond angles? o EXERCISE!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 5 What is the valence electron configuration of a carbon atom? s2p2 s2p2 Why can’t the bonding orbitals for methane be formed by an overlap of atomic orbitals? CONCEPT CHECK!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 6 Bonding in Methane  Assume that the carbon atom has four equivalent atomic orbitals, arranged tetrahedrally.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 7 Hybridization  Mixing of the native atomic orbitals to form special orbitals for bonding.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 8 sp 3 Hybridization  Combination of one s and three p orbitals.  Whenever a set of equivalent tetrahedral atomic orbitals is required by an atom, the localized electron model assumes that the atom adopts a set of sp 3 orbitals; the atom becomes sp 3 hybridized.  The four orbitals are identical in shape.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 9 An Energy-Level Diagram Showing the Formation of Four sp 3 Orbitals

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 10 The Formation of sp 3 Hybrid Orbitals

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 11 Tetrahedral Set of Four sp 3 Orbitals

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 12 Draw the Lewis structure for C 2 H 4 (ethylene)?  What is the shape of an ethylene molecule? trigonal planar around each carbon atom  What are the approximate bond angles around the carbon atoms? 120 o EXERCISE!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 13 Why can’t sp 3 hybridization account for the ethylene molecule? CONCEPT CHECK!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 14 sp 2 Hybridization  Combination of one s and two p orbitals.  Gives a trigonal planar arrangement of atomic orbitals.  One p orbital is not used.  Oriented perpendicular to the plane of the sp 2 orbitals.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 15 Sigma ( Σ ) Bond  Electron pair is shared in an area centered on a line running between the atoms.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 16 Pi ( Π ) Bond  Forms double and triple bonds by sharing electron pair(s) in the space above and below the σ bond.  Uses the unhybridized p orbitals.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 17 An Orbital Energy-Level Diagram for sp 2 Hybridization

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 18 The Hybridization of the s, p x, and p y Atomic Orbitals

Section 9.1 Hybridization and the Localized Electron Model Formation of C=C Double Bond in Ethylene Copyright © Cengage Learning. All rights reserved 19 To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 20 Draw the Lewis structure for CO 2.  What is the shape of a carbon dioxide molecule? linear  What are the bond angles? 180 o EXERCISE!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 21 sp Hybridization  Combination of one s and one p orbital.  Gives a linear arrangement of atomic orbitals.  Two p orbitals are not used.  Needed to form the π bonds.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 22 The Orbital Energy-Level Diagram for the Formation of sp Hybrid Orbitals on Carbon

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 23 When One s Orbital and One p Orbital are Hybridized, a Set of Two sp Orbitals Oriented at 180 Degrees Results

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 24 The Orbitals for CO 2

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 25 Draw the Lewis structure for PCl 5.  What is the shape of a phosphorus pentachloride molecule? trigonal bipyramidal  What are the bond angles? 90 o and 120 o EXERCISE!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 26 dsp 3 Hybridization  Combination of one d, one s, and three p orbitals.  Gives a trigonal bipyramidal arrangement of five equivalent hybrid orbitals.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 27 The Orbitals Used to Form the Bonds in PCl 5

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 28 Draw the Lewis structure for XeF 4.  What is the shape of a xenon tetrafluoride molecule? octahedral  What are the bond angles? 90 o and 180 o EXERCISE!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 29 d 2 sp 3 Hybridization  Combination of two d, one s, and three p orbitals.  Gives an octahedral arrangement of six equivalent hybrid orbitals.

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 30 How is the Xenon Atom in XeF 4 Hybridized?

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 31 Draw the Lewis structure for HCN. Which hybrid orbitals are used? Draw HCN:  Showing all bonds between atoms.  Labeling each bond as σ or π. CONCEPT CHECK!

Section 9.1 Hybridization and the Localized Electron Model Determine the bond angle and expected hybridization of the central atom for each of the following molecules: NH 3 SO 2 KrF 2 CO 2 ICl 5 NH 3 – o, sp 3 SO 2 – 120 o, sp 2 KrF 2 – 90 o, 120 o, dsp 3 CO 2 – 180 o, sp ICl 5 – 90 o, 180 o, d 2 sp 3 CONCEPT CHECK!

Section 9.1 Hybridization and the Localized Electron Model Copyright © Cengage Learning. All rights reserved 33 Using the Localized Electron Model  Draw the Lewis structure(s).  Determine the arrangement of electron pairs using the VSEPR model.  Specify the hybrid orbitals needed to accommodate the electron pairs.

Section 9.4 Bonding in Heteronuclear Diatomic Molecules AP Learning Objectives, Margin Notes and References  Learning Objectives  LO 2.18 The student is able to rank and justify the ranking of bond polarity on the basis of the locations of the bonded atoms in the periodic table.

Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecules  Composed of 2 different atoms. Copyright © Cengage Learning. All rights reserved 35

Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF  The 2p orbital of fluorine is at a lower energy than the 1s orbital of hydrogen because fluorine binds its valence electrons more tightly.  Electrons prefer to be closer to the fluorine atom.  Thus the 2p electron on a free fluorine atom is at a lower energy than the 1s electron on a free hydrogen atom. Copyright © Cengage Learning. All rights reserved 36

Section 9.4 Bonding in Heteronuclear Diatomic Molecules Orbital Energy-Level Diagram for the HF Molecule Copyright © Cengage Learning. All rights reserved 37

Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF  The diagram predicts that the HF molecule should be stable because both electrons are lowered in energy relative to their energy in the free hydrogen and fluorine atoms, which is the driving force for bond formation. Copyright © Cengage Learning. All rights reserved 38

Section 9.4 Bonding in Heteronuclear Diatomic Molecules The Electron Probability Distribution in the Bonding Molecular Orbital of the HF Molecule Copyright © Cengage Learning. All rights reserved 39

Section 9.4 Bonding in Heteronuclear Diatomic Molecules Heteronuclear Diatomic Molecule: HF  The σ molecular orbital containing the bonding electron pair shows greater electron probability close to the fluorine.  The electron pair is not shared equally.  This causes the fluorine atom to have a slight excess of negative charge and leaves the hydrogen atom partially positive.  This is exactly the bond polarity observed for HF. Copyright © Cengage Learning. All rights reserved 40

Section 9.6 Photoelectron Spectroscopy (PES) AP Learning Objectives, Margin Notes and References  Learning Objectives  LO 1.7 The student is able to describe the electron structure of the atom, using PES (photoelectron spectroscopy) data, ionization energy data, and/or Coulomb’s Law to construct explanations of how the energies of electrons within shells in atoms vary.  LO 1.15 The student can justify the selection of a particular type of spectroscopy to measure properties associated with vibrational or electronic motions of molecules.  LO 2.21 The student is able to use Lewis diagrams and VSEPR to predict the geometry of molecules, identify hybridization, and make predictions about polarity.  Additional AP References  LO 1.15 (see APEC #1 “Energy Levels and Electron Transitions”)  LO 1.15 (see Appendix 7.4 “Molecular Spectroscopy: An Introduction”)

Section 9.6 Photoelectron Spectroscopy (PES) Copyright © Cengage Learning. All rights reserved 42  Can be used to determine the relative energies of electrons in individual atoms and molecules.  High-energy photons are directed at the sample, and the kinetic energies of the ejected electrons are measured.