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VBT and Hybridization
 

VBT and Hybridization

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  • very good , thanks vvvveeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeery much
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  • thanks Ma'am! :D
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  • I'm truly sorry for the late upload. For n hours, 'slideshare fail.' Pero oks na sa wakas! Yay! Happy reviewing! :)

    Btw, the Chem probsets are taken during class hours, NOT take home. So please do review: Lewis structures ---> Hybridization. See you tomorrow! ;D
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    VBT and Hybridization VBT and Hybridization Presentation Transcript

      • Lewis structures and VSEPR do not explain why a bond forms. How do we account for shape in terms of quantum mechanics?
      • What are the orbitals that are involved in bonding?
      • We use Valence Bond Theory:
        • Bonds form when orbitals on atoms overlap.
          • A covalent bond forms when the orbitals of two atoms overlap and the overlap region, which is between the nuclei, is occupied by a pair of electrons.
        • There are two electrons of opposite spin in the orbital overlap.
      Covalent Bonding and Orbital Overlap
    • Covalent Bonding and Orbital Overlap Hydrogen, H 2
    • Hydrogen fluoride, HF Fluorine, F 2
      • As two nuclei approach each other their atomic orbitals overlap.
      • As the amount of overlap increases, the energy of the interaction decreases.
      • At some distance the minimum energy is reached.
      • The minimum energy corresponds to the bonding distance (or bond length).
      • As the two atoms get closer, their nuclei begin to repel and the energy increases.
      Covalent Bonding and Orbital Overlap
      • At the bonding distance, the attractive forces between nuclei and electrons just balance the repulsive forces (nucleus-nucleus, electron-electron).
      Covalent Bonding and Orbital Overlap
    •  
      • Atomic orbitals can mix or hybridize in order to adopt an appropriate geometry for bonding.
      • Hybridization is determined by the electron domain geometry.
      • sp Hybrid Orbitals
      • Consider the BeF 2 molecule (experimentally known to exist):
      Hybrid Orbitals
      • sp Hybrid Orbitals
        • Be has a 1s 2 2s 2 electron configuration.
        • There is no unpaired electron available for bonding.
        • We conclude that the atomic orbitals are not adequate to describe orbitals in molecules.
      • We know that the F-Be-F bond angle is 180  (VSEPR theory).
      • We also know that one electron from Be is shared with each one of the unpaired electrons from F.
      Hybrid Orbitals
      • sp Hybrid Orbitals
      • We assume that the Be orbitals in the Be-F bond are 180  apart.
        • We could promote and electron from the 2 s orbital on Be to the 2 p orbital to get two unpaired electrons for bonding.
          • BUT the geometry is still not explained.
      • We can solve the problem by allowing the 2 s and one 2 p orbital on Be to mix or form a hybrid orbital.
      • The hybrid orbital comes from an s and a p orbital and is called an sp hybrid orbital.
      Hybrid Orbitals
    •  
      • sp Hybrid Orbitals
      • The lobes of sp hybrid orbitals are 180 º apart .
      • Since only one of the Be 2 p orbitals has been used in hybridization, there are two unhybridized p orbitals remaining on Be.
      Hybrid Orbitals
    • Figure 11.2 The sp hybrid orbitals in gaseous BeCl 2 . atomic orbitals hybrid orbitals orbital box diagrams
    • Figure 11.2 The sp hybrid orbitals in gaseous BeCl 2 (continued). orbital box diagrams with orbital contours
    •  
    • Figure 11.3 The sp 2 hybrid orbitals in BF 3 .
    • sp 2 and sp 3 Hybrid Orbitals
    • Figure 11.4 The sp 3 hybrid orbitals in CH 4 .
    • Figure 11.5 The sp 3 hybrid orbitals in NH 3 .
    • Figure 11.5 continued The sp 3 hybrid orbitals in H 2 O.
    • Figure 11.6 The sp 3 d hybrid orbitals in PCl 5 .
    • Figure 11.7 The sp 3 d 2 hybrid orbitals in SF 6 .
    • Hybrid Orbitals The numbe r of hybrid orbitals obtained equals the number of atomic orbitals mixed. The type of hybrid orbitals obtained varies with the types of atomic orbitals mixed. Key Points sp sp 2 sp 3 sp 3 d sp 3 d 2 Types of Hybrid Orbitals
    •  
    • Figure 11.8 The conceptual steps from molecular formula to the hybrid orbitals used in bonding. Molecular formula Lewis structure Molecular shape and e - group arrangement Hybrid orbitals Step 1 Step 2 Step 3
    • SAMPLE PROBLEM 11.1 Postulating Hybrid Orbitals in a Molecule SOLUTION: (a) Methanol, CH 3 OH (b) Sulfur tetrafluoride, SF 4 (a) CH 3 OH The groups around C are arranged as a tetrahedron. O also has a tetrahedral arrangement with 2 nonbonding e - pairs. PROBLEM: Use partial orbital diagrams to describe mixing of the atomic orbitals of the central atom leads to hybrid orbitals in each of the following: PLAN: Use the Lewis structures to ascertain the arrangement of groups and shape of each molecule. Postulate the hybrid orbitals. Use partial orbital box diagrams to indicate the hybrid for the central atoms.
    • SAMPLE PROBLEM 11.1 Postulating Hybrid Orbitals in a Molecule continued (b) SF 4 has a seesaw shape with 4 bonding and 1 nonbonding e - pairs. single C atom hybridized C atom single O atom hybridized O atom S atom hybridized S atom
      • Hybridization Involving d Orbitals
      • Since there are only three p -orbitals, trigonal bipyramidal and octahedral electron domain geometries must involve d -orbitals.
      • Trigonal bipyramidal electron domain geometries require sp 3 d hybridization.
      • Octahedral electron domain geometries require sp 3 d 2 hybridization.
      • Note the electron domain geometry from VSEPR theory determines the hybridization.
      Hybrid Orbitals
      • Summary
      • Draw the Lewis structure.
      • Determine the electron domain geometry with VSEPR.
      • Specify the hybrid orbitals required for the electron pairs based on the electron domain geometry.
      Hybrid Orbitals
    •  
    •  
    • Multiple Bonds
      •  -Bonds: electron density lies on the axis between the nuclei.
      • All single bonds are  -bonds.
      •  -Bonds: electron density lies above and below the plane of the nuclei.
      • A double bond consists of one  -bond and one  -bond.
      • A triple bond has one  -bond and two  -bonds.
      • Often, the p -orbitals involved in  -bonding come from unhybridized orbitals.
    • Multiple Bonds
    • Figure 11.9 The  bonds in ethane(C 2 H 6 ). both C are sp 3 hybridized s-sp 3 overlaps to  bonds sp 3 -sp 3 overlap to form a  bond relatively even distribution of electron density over all  bonds
    • Multiple Bonds
      • Ethylene, C 2 H 4 , has:
        • one  - and one  -bond;
        • both C atoms sp 2 hybridized;
        • both C atoms with trigonal planar electron pair and molecular geometries.
    • Figure 11.10 The  and  bonds in ethylene (C 2 H 4 ). overlap in one position -  p overlap -  electron density
    • Multiple Bonds
    •  
    • Multiple Bonds
      • When triple bonds form (e.g. N 2 ) one  -bond is always above and below and the other is in front and behind the plane of the nuclei.
    • Multiple Bonds
      • Consider acetylene, C 2 H 2
        • the electron pair geometry of each C is linear;
        • therefore, the C atoms are sp hybridized;
        • the sp hybrid orbitals form the C-C and C-H  -bonds;
        • there are two unhybridized p -orbitals;
        • both unhybridized p -orbitals form the two  -bonds;
        • one  -bond is above and below the plane of the nuclei;
        • one  -bond is in front and behind the plane of the nuclei.
    • Figure 11.11 The  and  bonds in acetylene (C 2 H 2 ). overlap in one position -  p overlap - 
    • Prentice Hall © 2003 Chapter 9 Multiple Bonds
    • Multiple Bonds
      • QUIZ # 2: (29 June 2010)
      • Draw the most stable Lewis Structure of CH 3 CN.
      • Show the hybridization of atoms.
      • Draw the Molecular Geometry and label all orbitals and bonds ( ơ , п ).
      • Count the number of ơ and п bonds.
      For # 3, you can also use the skeletal structure.