Review Chapter 10: Theories of Bonding & Structure. Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson, Brady, & Hyslop

Transcription

1 Review Chapter 10: Theories of Bonding & Structure Chemistry: The Molecular Nature of Matter, 6 th edition By Jesperson, Brady, & Hyslop

2 Chapter 10 Concepts q VESPR theory q Predict molecular geometry & overall dipole moment q Valence Bond Theory q Identify & draw hybridization of orbitals at central atom q Predict molecular geometry & overall dipole moment q Identify & draw σ and π bonds q Molecular Orbital Theory q Draw MO Energy Diagrams to identify q Bond Order q Number of Unpaired Electrons 2

3 Memorize Linear Trigonal Planar or Planar Triangular Trigonal Bipyramidal Tetrahedral Octahedral

4 Memorize Trigonal Pyramidal T-shaped Bent Square Pyramid Seesaw or Distorted Tetrahedron Square Planar

5 Determining 3-D VESPR Stuctures 1. Draw Lewis Structure of Molecule Don't need to compute formal charge If several resonance structures exist, pick only one 2. Count electron pair domains Lone pairs and bond pairs around central atom Mul?ple bonds count as one set (or one effec?ve pair) 3. Arrange electron pair domains to minimize repulsions Lone pairs Require more space than bonding pairs May slightly distort bond angles from those predicted. In trigonal bipyramid lone pairs are equatorial In octahedron lone pairs are axial 4. Name molecular structure by posibon of atoms only bonding electrons

6 Polarity If symmetrical polar bonds around a central atom then they cancel and there is no overall dipole moment. Molecule is usually polar if All atoms agached to central atom are NOT same, OR There are one or more lone pairs on central atom EXCEPT:

7 Valence Bond Theory Valence Bond Theory Individual atoms, each have their own orbitals and orbitals overlap to form bonds. Extent of overlap of atomic orbitals is related to bond strength Hybridization = mixing atomic orbitals sp: Linear sp 3 d: Trigonal Bipyramidal sp 2 : Planar Triangular sp 3 : Tetrahedral sp 3 d 2 : Octahedral

8 1) Draw lewis dot structure Valence Bond Theory 2) How many lone pairs & bonded atoms will repel one another? That is the number of hybrid orbitals needed 2: sp 3: sp 2 4: sp 3 5: sp 3 d 6: sp 3 d 2 3) Convert the needed number of atomic orbitals into hybridized orbitals. 4) Fill in valence electrons. Remember that any p orbitals will be close enough in energy that they both hybrid & remaining p orbitals will fill half way with electrons before they pair. 5) Draw hybrid orbitals equally spaced around the central atom: a) Form σ bonds using hybrid orbitals with one electron b) Hybrid orbitals with two electrons are likely lone pairs c) If any lone electrons are in p orbitals π bonds will form 6) Describe molecular geometry around central atom(s).

9 Valence Bond Theory: Example N 2 :N N: E p s AO of N p sp Hybrid & AO of N Lone pair and atom bonded to Nitrogen will repel each other. Therefore, need to hybridize 2 orbitals One hybrid orbital with one electron will par?cipate in a σ bond with the other nitrogen The other hybrid orbital contains a lone pair 2 p orbitals each have 1 electron so form 2 π bonds to the other nitrogen

10 Molecular Orbital Theory Molecular Orbital Theory Views molecule as collection of positively charged nuclei having a set of molecular orbitals that are filled with electrons (similar to filling atomic orbitals with electrons). Doesn't worry about how atoms come together to form molecule!"#$%"&$'&%(% )#*+,'&%"-%,"#$.#/%e )! )#*+,'&%"-%0#1.,"#$.#/%e ) 2%'3'41&"#56,"#$

11 Molecular Orbital Theory Li 2 N 2 π 2p Lower in energy than σ 2p O 2, F 2 and Higher σ 2p Lower in energy than π 2p Can ignore filled 1s bonding & anbbonding and focus on valence electrons

12 Molecular Orbital Theory: Diagrams σ* π* E p π σ s σ* AO of one atom σ AO of second atom

13 Problem Set A 1. For the following molecules: a. Draw a lewis dot structure. b. Determine the molecular geometry at each central atom. c. Iden?fy the bond angles. d. Iden?fy all polar bonds: δ+ / δ- e. Assess the polarity of the molecule & indicate the overall dipole moment if one exists AsF 5 AsF 3 SeO 2 GaH 3 ICl2 - SiO 4-4 TeF6 13

14 Problem Set B 2. What is the hybridiza?on of oxygen in OCl 2? 3. For the species and XeF 4 O, determine the following: a. electron domain geometry (geometry including non- bonding pairs) b. molecular geometry c. Hybridiza?on around central atom d. Polarity 4. How many σ and π bonds are there in CH 2 CHCHCH 2, and what is the hybridiza?on around the carbon atoms? 5. Draw & list the bonding orbitals for HCN. 14

15 Problem Set C 6. What is the MO Energy Diagram for B 2? How many unpaired electrons does B 2 have? 7. What is the bond order & number of unpaired electrons +! in O, O, and O? Draw the MO Energy Diagram for BN. 15

16 Problem Set A 16

17 Problem Set A 17

18 Problem Set A 18

19 Problem Set B 2. sp 3 3. XeF 4 O: octahedral, square pyramid, sp 3 d 2, polar 4. 9, 2, sp 2 5. HCN: C will be create a σ bond to H and N with sp 2 hybridized orbitals and use 2 p orbitals to par?cipate in 2 π bonds with N. N will par?cipate in the σ bond with C with an sp 2 hybridized orbital, the other will hold the N lone pair, and then N will use 2 p orbitals to π bond with C. 19

20 Problem Set C B 2 BN 6. MO B 2 : unpaired e- = 2 σ* π* σ* π* 7. O 2 : BO = 2 unpaired e- = 2 O 2+ : BO = 5/2 unpaired e- = 1 O 2 - : BO = 3/2 unpaired e- = 1 σ π σ π 8. MO BN: σ* σ* σ σ 20

21 More Practice Problems: Analyze the following compounds: 1. Draw the lewis dot structure 2. Determine the Geometry using VESPR theory 3. Determine the hybridization at any central atoms using VB Theory 4. Draw & Describe bonding in VB terms: ie # of sigma vs pi bonds H 2 S SO 2 H 2 C=C=CH 2 HCOCl