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Chemistry: A Molecular Approach, 2nd Ed. Nivaldo Tro Chapter 10 Chemical Bonding II Tro: Chemistry: A Molecular Approach, 2/e Copyright 2011 Pearson Education, Inc. Structure Determines Properties! • Properties of molecular substances depend on • the structure of the molecule The structure includes many factors, such as: __________________________________ __________________________________ ionic, polar covalent, or covalent __________________________________ • Bonding theory should allow you to predict the shapes of molecules Tro: Chemistry: A Molecular Approach, 2/e 2 Copyright 2011 Pearson Education, Inc. Molecular Geometry • Molecules are 3-dimensional objects • We often describe the shape of a molecule • • with terms that relate to _______________ These geometric figures have characteristic “corners” that indicate the positions of the surrounding atoms around a central atom in the center of the geometric figure The geometric figures also have characteristic angles that we call _______________________________ Tro: Chemistry: A Molecular Approach, 2/e 3 Copyright 2011 Pearson Education, Inc. Lewis Theory Predicts Electron Groups • Lewis theory predicts there are regions of • • electrons in an atom Some regions result from placing shared pairs of valence electrons between bonding nuclei Other regions result from placing unshared valence electrons on a single nuclei Tro: Chemistry: A Molecular Approach, 2/e 4 Copyright 2011 Pearson Education, Inc. Using Lewis Theory to Predict Molecular Shapes • Lewis theory says that these regions of electron groups should repel each other ______________________________________ • This idea can then be extended to predict the shapes of molecules the position of atoms surrounding a central atom will be determined by _______________________________ the positions of the electron groups will be determined by trying to __________________________________ Tro: Chemistry: A Molecular Approach, 2/e 5 Copyright 2011 Pearson Education, Inc. VSEPR Theory • Electron groups around the central atom will be most stable when they are as far apart as possible – we call this _____________________________________ _theory because electrons are negatively charged, they should be most stable when they are separated as much as possible • The resulting geometric arrangement will allow us to predict the shapes and bond angles in the molecule Tro: Chemistry: A Molecular Approach, 2/e 6 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 7 Copyright 2011 Pearson Education, Inc. Electron Groups • The Lewis structure predicts the number of valence • • electron pairs around the central atom(s) Each ________________of electrons constitutes ________________on a central atom Each ___________constitutes _____________on a central atom regardless of whether it is single, double, or triple •• •O • •• N •• O •• •• Tro: Chemistry: A Molecular Approach, 2/e there are three electron groups on N ________________________ ________________________ ________________________ 8 Copyright 2011 Pearson Education, Inc. Electron Group Geometry • There are ___________________of electron groups around a central atom based on a maximum of six bonding electron groups though there may be more than six on very large atoms, it is very rare • Each of these five basic arrangements results in _____________ different basic electron geometries in order for the molecular shape and bond angles to be a “perfect” geometric figure, all the electron groups must be bonds and all the bonds must be equivalent • For molecules that exhibit _____________, it doesn’t matter which resonance form you use – the electron geometry will be the same Tro: Chemistry: A Molecular Approach, 2/e 9 Copyright 2011 Pearson Education, Inc. Linear Electron Geometry • When there are two electron groups around the • • central atom, they will occupy positions on opposite sides of the central atom This results in the electron groups taking a ________________________ (add bond angle to your vsepr chart!) The bond angle is 180° Tro: Chemistry: A Molecular Approach, 2/e 10 Copyright 2011 Pearson Education, Inc. Linear Geometry Tro: Chemistry: A Molecular Approach, 2/e 11 Copyright 2011 Pearson Education, Inc. Trigonal Planar Electron Geometry • When there are three electron groups around • • the central atom, they will occupy positions in the shape of a triangle around the central atom This results in the electron groups taking a ____________________ The bond angle _________ Tro: Chemistry: A Molecular Approach, 2/e 12 Copyright 2011 Pearson Education, Inc. Trigonal Geometry Tro: Chemistry: A Molecular Approach, 2/e 13 Copyright 2011 Pearson Education, Inc. Tetrahedral Electron Geometry • When there are four electron groups around the • • central atom, they will occupy positions in the shape of a tetrahedron around the central atom This results in the electron groups taking a ______________________ The bond angle is ____________° Tro: Chemistry: A Molecular Approach, 2/e 14 Copyright 2011 Pearson Education, Inc. Tetrahedral Geometry Tro: Chemistry: A Molecular Approach, 2/e 15 Copyright 2011 Pearson Education, Inc. Trigonal Bipyramidal Electron Geometry • When there are five electron groups around the central • • • • atom, they will occupy positions in the shape of two tetrahedra that are base-to-base with the central atom in the center of the shared bases This results in the electron groups taking a ________________________________ The positions above and below the central atom are called the ________________ positions The positions in the same base plane as the central atom are called the ______________equatorial positions is 120° The bond angle between axial and equatorial positions is 90° Tro: Chemistry: A Molecular Approach, 2/e 16 Copyright 2011 Pearson Education, Inc. Trigonal Bipyramid Tro: Chemistry: A Molecular Approach, 2/e 17 Copyright 2011 Pearson Education, Inc. Trigonal Bipyramidal Geometry Tro: Chemistry: A Molecular Approach, 2/e 18 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 19 Copyright 2011 Pearson Education, Inc. Octahedral Electron Geometry • When there are six electron groups around the central atom, they will occupy positions in the shape of two square-base pyramids that are base-to-base with the central atom in the center of the shared bases • This results in the electron groups taking an ___________________________ it is called octahedral because the geometric figure has eight sides • All positions are equivalent • The bond angle ___________________° Tro: Chemistry: A Molecular Approach, 2/e 20 Copyright 2011 Pearson Education, Inc. Octahedral Geometry Tro: Chemistry: A Molecular Approach, 2/e 21 Copyright 2011 Pearson Education, Inc. Octahedral Geometry Tro: Chemistry: A Molecular Approach, 2/e 22 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 23 Copyright 2011 Pearson Education, Inc. Molecular Geometry • The actual geometry of the molecule may be different from the electron geometry • When the electron groups are attached to atoms of different size, or when the bonding to one atom is different than the bonding to another, this will affect the molecular geometry around the central atom • _____________________________________ they occupy space on the central atom, but are not “seen” as points on the molecular geometry Tro: Chemistry: A Molecular Approach, 2/e 24 Copyright 2011 Pearson Education, Inc. Not Quite Perfect Geometry Because the bonds and atom sizes are not identical in formaldehyde, the observed angles are slightly different from ideal Tro: Chemistry: A Molecular Approach, 2/e 25 Copyright 2011 Pearson Education, Inc. The Effect of Lone Pairs • Lone pair groups “occupy more space” on the central atom because their electron density is exclusively on the central atom rather than shared like bonding electron groups • Relative sizes of repulsive force interactions is Lone Pair – Lone Pair > Lone Pair – Bonding Pair > Bonding Pair – Bonding Pair • This affects the bond angles, making the bonding pair – bonding pair angles smaller than expected Tro: Chemistry: A Molecular Approach, 2/e 26 Copyright 2011 Pearson Education, Inc. Effect of Lone Pairs bonding electrons are are shared by twoon The nonbonding electrons localized atoms, so some negative charge is the central atom,ofsothe area of negative charge removed from the central atom takes more space Tro: Chemistry: A Molecular Approach, 2/e 27 Copyright 2011 Pearson Education, Inc. Bond Angle Distortion from Lone Pairs Tro: Chemistry: A Molecular Approach, 2/e 28 Copyright 2011 Pearson Education, Inc. Bond Angle Distortion from Lone Pairs Tro: Chemistry: A Molecular Approach, 2/e 29 Copyright 2011 Pearson Education, Inc. Bent Molecular Geometry: Derivative of Trigonal Planar Electron Geometry • When there are three electron groups around • the central atom, and one of them is a lone pair, the resulting shape of the molecule is called a ______________________________________ The bond angle is less than 120° because the lone pair takes up more space Tro: Chemistry: A Molecular Approach, 2/e 30 Copyright 2011 Pearson Education, Inc. Pyramidal & Bent Molecular Geometries: Derivatives of Tetrahedral Electron Geometry • When there are four electron groups around the central atom, and one is a lone pair, the result is called a __________________________ because it is a triangular-base pyramid with the central atom at the apex • When there are four electron groups around the central atom, and two are lone pairs, the result is called a ___________________________ it is planar it looks similar to the trigonal planar—bent shape, except the angles are smaller • For both shapes, the bond angle is less than ________________. Tro: Chemistry: A Molecular Approach, 2/e 31 Copyright 2011 Pearson Education, Inc. Methane Tro: Chemistry: A Molecular Approach, 2/e 32 Copyright 2011 Pearson Education, Inc. Pyramidal Shape Tro: Chemistry: A Molecular Approach, 2/e 33 Copyright 2011 Pearson Education, Inc. Pyramidal Shape Tro: Chemistry: A Molecular Approach, 2/e 34 Copyright 2011 Pearson Education, Inc. Tetrahedral–Bent Shape Tro: Chemistry: A Molecular Approach, 2/e 35 Copyright 2011 Pearson Education, Inc. Tetrahedral–Bent Shape Tro: Chemistry: A Molecular Approach, 2/e 36 Copyright 2011 Pearson Education, Inc. Derivatives of the Trigonal Bipyramidal Electron Geometry • When there are five electron groups around the central atom, • and some are lone pairs, they will occupy the equatorial positions because there is more room When there are five electron groups around the central atom, and one is a lone pair, the result is called the __________________ aka distorted tetrahedron • When there are five electron groups around the central atom, • and two are lone pairs, the result is called the ____________ When there are five electron groups around the central atom, and three are lone pairs, the result is a ________________ • The bond angles between equatorial positions are less than _______ • The bond angles between axial and equatorial positions are less than ___° linear = 180° axial–to–axial Tro: Chemistry: A Molecular Approach, 2/e 37 Copyright 2011 Pearson Education, Inc. Replacing Atoms with Lone Pairs in the Trigonal Bipyramid System Tro: Chemistry: A Molecular Approach, 2/e 38 Copyright 2011 Pearson Education, Inc. Seesaw Shape Tro: Chemistry: A Molecular Approach, 2/e 39 Copyright 2011 Pearson Education, Inc. T–Shape Tro: Chemistry: A Molecular Approach, 2/e 40 Copyright 2011 Pearson Education, Inc. T–Shape Tro: Chemistry: A Molecular Approach, 2/e 41 Copyright 2011 Pearson Education, Inc. Linear Shape Tro: Chemistry: A Molecular Approach, 2/e 42 Copyright 2011 Pearson Education, Inc. Derivatives of the Octahedral Geometry • When there are six electron groups around the • central atom, and some are lone pairs, each even number lone pair will take a position opposite the previous lone pair When there are six electron groups around the central atom, and one is a lone pair, the result is called a ___________________ the bond angles between axial and equatorial positions is less than 90° • When there are six electron groups around the central atom, and two are lone pairs, the result is called a ____________________ the bond angles between equatorial positions is 90° Tro: Chemistry: A Molecular Approach, 2/e 43 Copyright 2011 Pearson Education, Inc. Square Pyramidal Shape Tro: Chemistry: A Molecular Approach, 2/e 44 Copyright 2011 Pearson Education, Inc. Square Planar Shape Tro: Chemistry: A Molecular Approach, 2/e 45 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 46 Copyright 2011 Pearson Education, Inc. Predicting the Shapes Around Central Atoms 1. Draw the Lewis structure 2. Determine the number of electron groups around the central atom 3. Classify each electron group as bonding or lone pair, and count each type remember, ____________________________ 4. Use Table 10.1 to determine the shape and bond angles Tro: Chemistry: A Molecular Approach, 2/e 47 Copyright 2011 Pearson Education, Inc. Example 10.2: Predict the geometry and bond angles of PCl3 1. Draw the Lewis structure a) _____ valence electrons 2. Determine the Number of electron groups around central atom a) ______ electron groups around P Tro: Chemistry: A Molecular Approach, 2/e 48 Copyright 2011 Pearson Education, Inc. Example 10.2: Predict the geometry and bond angles of PCl3 3. Classify the electron groups a) _______ bonding groups b) _______ lone pair 4. Use Table 10.1 to determine the shape and bond angles a) four electron groups around P = __________ electron geometry b) three bonding + one lone pair = ____________molecular geometry c) trigonal pyramidal = bond angles less than ________° Tro: Chemistry: A Molecular Approach, 2/e 49 Copyright 2011 Pearson Education, Inc. Practice – Predict the molecular geometry and bond angles in SiF5− Tro: Chemistry: A Molecular Approach, 2/e 50 Copyright 2011 Pearson Education, Inc. Practice – Predict the molecular geometry and bond angles in ClO2F Tro: Chemistry: A Molecular Approach, 2/e 51 Copyright 2011 Pearson Education, Inc. Representing 3-Dimensional Shapes on a 2-Dimensional Surface • One of the problems with drawing molecules is • • • • trying to show their dimensionality By convention, the central atom is put in the plane of the paper Put as many other atoms as possible in the same plane and indicate with a ________________ For atoms in front of the plane, use a _________ For atoms behind the plane, use a ___________ Tro: Chemistry: A Molecular Approach, 2/e 52 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 53 Copyright 2011 Pearson Education, Inc. SF6 F F F S F F F Tro: Chemistry: A Molecular Approach, 2/e 54 Copyright 2011 Pearson Education, Inc. Multiple Central Atoms • Many molecules have larger structures with many • • interior atoms We can think of them as having multiple central atoms When this occurs, we describe the shape around each central atom in sequence shape around left C is _______________ shape around center C is ___________ shape around right O is _____________ Tro: Chemistry: A Molecular Approach, 2/e 55 H O | || H C C O H | H Copyright 2011 Pearson Education, Inc. Describing the Geometry of Methanol Tro: Chemistry: A Molecular Approach, 2/e 56 Copyright 2011 Pearson Education, Inc. Describing the Geometry of Glycine Tro: Chemistry: A Molecular Approach, 2/e 57 Copyright 2011 Pearson Education, Inc. Practice – Predict the molecular geometries in H3BO3 Tro: Chemistry: A Molecular Approach, 2/e 58 Copyright 2011 Pearson Education, Inc. Polarity of Molecules • For a molecule to be polar it must 1. have polar bonds _______________________- theory _________________ - measured 2. have an unsymmetrical shape _________________________ • Polarity affects the intermolecular forces of attraction therefore ______________and _____________ like dissolves like • Nonbonding pairs affect molecular polarity, strong pull in its direction Tro: Chemistry: A Molecular Approach, 2/e 59 Copyright 2011 Pearson Education, Inc. Molecule Polarity The H─Cl bond is polar. The bonding electrons are pulled toward the Cl end of the molecule. The net result is a polar molecule. Tro: Chemistry: A Molecular Approach, 2/e 60 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 61 Copyright 2011 Pearson Education, Inc. Molecule Polarity The O─C bond ___________. The bonding electrons are pulled equally toward both O ends of the molecule. The net result is a _____________ molecule. Tro: Chemistry: A Molecular Approach, 2/e 62 Copyright 2011 Pearson Education, Inc. Molecule Polarity The H─O bond is _________. Both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a _________ molecule. Tro: Chemistry: A Molecular Approach, 2/e 63 Copyright 2011 Pearson Education, Inc. Predicting Polarity of Molecules 1. Draw the Lewis structure and determine the molecular geometry 2. Determine whether the bonds in the molecule are polar a) if there are not polar bonds, the molecule is nonpolar 3. Determine whether the polar bonds add together to give a net dipole moment Tro: Chemistry: A Molecular Approach, 2/e 64 Copyright 2011 Pearson Education, Inc. Example 10.5: Predict whether NH3 is a polar molecule 1. Draw the Lewis structure and determine the molecular geometry a) ___________ valence electrons b) three bonding + one lone pair = ___________molecular geometry Tro: Chemistry: A Molecular Approach, 2/e 65 Copyright 2011 Pearson Education, Inc. Example 10.5: Predict whether NH3 is a polar molecule 2. Determine if the bonds are polar a) ____________difference b) if the bonds are not polar, we can stop here and declare the molecule will be nonpolar Tro: Chemistry: A Molecular Approach, 2/e 66 ENN = 3.0 ENH = 2.1 3.0 − 2.1 = ____ therefore the bonds are ___________ Copyright 2011 Pearson Education, Inc. Example 10.5: Predict whether NH3 is a polar molecule 3) Determine whether the polar bonds add together to give a net dipole moment a) ______ addition b) generally, asymmetric shapes result in uncompensated polarities and a net dipole moment Tro: Chemistry: A Molecular Approach, 2/e 67 The H─N bond is polar. All the sets of bonding electrons are pulled toward the N end of the molecule. The net result is a polar molecule. Copyright 2011 Pearson Education, Inc. Practice – Decide whether the following molecules are polar EN O = 3.5 N = 3.0 Cl = 3.0 S = 2.5 Tro: Chemistry: A Molecular Approach, 2/e 68 Copyright 2011 Pearson Education, Inc. Molecular Polarity Affects Solubility in Water • Polar molecules are • ________to other polar molecules Because water is a _____ molecule, other _____ molecules dissolve well in water and ionic compounds as well • Some molecules have both 69 polar and nonpolar parts Tro: Chemistry: A Molecular Approach, 2/e Copyright 2011 Pearson Education, Inc. Orbital Diagram for the Formation of H2S H 1s ↑ + ↑↓ 1s ↑ 3s ↑ ↑ ↑↓ S 3p ↑↓ H─S bond ↑↓ H─S bond H Predicts bond angle = 90° Actual bond angle = 92° Tro: Chemistry: A Molecular Approach, 2/e 70 Copyright 2011 Pearson Education, Inc. Valence Bond Theory – Hybridization • One of the issues that arises is that the number of partially filled or empty atomic orbitals did not predict the number of bonds or orientation of bonds C = 2s22px12py12pz0 would predict two or three bonds that are 90° apart, rather than four bonds that are 109.5° apart • To adjust for these inconsistencies, it was postulated that the valence atomic orbitals could _____________ before bonding took place one hybridization of C is to mix all the 2s and 2p orbitals to get four orbitals that point at the corners of a tetrahedron Tro: Chemistry: A Molecular Approach, 2/e 71 Copyright 2011 Pearson Education, Inc. Unhybridized C Orbitals Predict the Wrong Bonding & Geometry Tro: Chemistry: A Molecular Approach, 2/e 72 Copyright 2011 Pearson Education, Inc. Valence Bond Theory Main Concepts 1. The valence electrons of the atoms in a molecule reside in quantum-mechanical atomic orbitals. The orbitals can be the standard s, p, d, and f orbitals, _______________combinations of these. 2. A chemical bond results when these atomic orbitals interact and there is a total of two electrons in the new molecular orbital a) _____________________ 3. The shape of the molecule is determined by the geometry of the interacting orbitals Tro: Chemistry: A Molecular Approach, 2/e 73 Copyright 2011 Pearson Education, Inc. Hybridization • Some atoms hybridize their orbitals to • maximize bonding • more bonds = more full orbitals = more stability ______________ is mixing different types of orbitals in the valence shell to make a new set of degenerate orbitals sp, sp2, sp3, sp3d, sp3d2 • Same type of atom can have different types of hybridization C = sp, sp2, sp3 Tro: Chemistry: A Molecular Approach, 2/e 74 Copyright 2011 Pearson Education, Inc. Hybrid Orbitals • The number of standard atomic orbitals combined = the number of hybrid orbitals formed combining a 2s with a 2p gives ____________orbitals H cannot hybridize!! its valence shell only has one orbital • The number and type of standard atomic orbitals • combined determines ___________of the hybrid orbitals The particular kind of hybridization that occurs is the one that yields the lowest overall energy for the molecule Tro: Chemistry: A Molecular Approach, 2/e 75 Copyright 2011 Pearson Education, Inc. Carbon Hybridizations Unhybridized 2p 2s sp hybridized 2sp 2p sp2 hybridized 2sp2 sp3 hybridized 2p 2sp3 Tro: Chemistry: A Molecular Approach, 2/e 76 Copyright 2011 Pearson Education, Inc. sp3 Hybridization • Atom with four electron groups around it ___________________etry 109.5° angles between hybrid orbitals • Atom uses hybrid orbitals for all bonds and lone pairs Tro: Chemistry: A Molecular Approach, 2/e 77 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 78 Copyright 2011 Pearson Education, Inc. Orbital Diagram of the sp3 Hybridization of C Tro: Chemistry: A Molecular Approach, 2/e 79 Copyright 2011 Pearson Education, Inc. sp3 Hybridized Atoms Orbital Diagrams • Place electrons into hybrid and unhybridized valence orbitals as if all the orbitals have equal energy • Lone pairs generally occupy hybrid orbitals sp3 hybridized atom Unhybridized atom 2s 2s 2p C 2p N Tro: Chemistry: A Molecular Approach, 2/e 80 2sp3 2sp3 Copyright 2011 Pearson Education, Inc. Practice – Draw the orbital diagram for the sp3 hybridization of each atom Unhybridized atom 3s 2s 3p Cl 3sp3 2p O 2sp3 Tro: Chemistry: A Molecular Approach, 2/e 81 sp3 hybridized atom Copyright 2011 Pearson Education, Inc. Bonding with Valence Bond Theory • According to valence bond theory, bonding takes place between atoms when their atomic or hybrid orbitals interact “overlap” • To interact, the orbitals must either be aligned • along the axis between the atoms, or The orbitals must be parallel to each other and perpendicular to the interatomic axis Tro: Chemistry: A Molecular Approach, 2/e 82 Copyright 2011 Pearson Education, Inc. Methane Formation with sp3 C Tro: Chemistry: A Molecular Approach, 2/e 83 Copyright 2011 Pearson Education, Inc. Ammonia Formation with sp3 N Tro: Chemistry: A Molecular Approach, 2/e 84 Copyright 2011 Pearson Education, Inc. Types of Bonds • A _____________results when the interacting atomic orbitals point along the axis connecting the two bonding nuclei either standard atomic orbitals or hybrids s–to–s, p–to–p, hybrid–to–hybrid, s–to–hybrid, etc. • A ______________results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei between unhybridized parallel p orbitals • The interaction between parallel orbitals is not as strong as between orbitals that point at each other; therefore _____________________________ Tro: Chemistry: A Molecular Approach, 2/e 85 Copyright 2011 Pearson Education, Inc. Tro: Chemistry: A Molecular Approach, 2/e 86 Copyright 2011 Pearson Education, Inc.