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Sparks CH301 How Can a Molecule Have Shape? Take a Closer Look at - - PowerPoint PPT Presentation
Sparks CH301 How Can a Molecule Have Shape? Take a Closer Look at - - PowerPoint PPT Presentation
Sparks CH301 How Can a Molecule Have Shape? Take a Closer Look at Shape & Bonding UNIT 3 Day 4 What are we going to learn today? Understand Bonding Theory Supporting Experimentally Determined Shapes (VB Theory - and bonds) Quiz:
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- 1. What is the electron configuration of N?
- A. 1s22s22p3
- C. 1s22s22p2
- B. 1s21p62s22p3
- D. 1s22s22p6
- 2. What is the shape of NH3?
- A. Tetrahedral
- C. Trigonal pyramidal
- B. Trigonal planar
- D. T-shaped
Quiz: Clicker Questions Think about bond angles in NH3. How get that bonding from the original s and p orbitals?
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Atomic Orbitals Molecular Shape
How is it that we get from atomic orbitals with characteristic shapes to these bonds? Overlapping orbitals – H2 HF
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Valence Bond Theory (VB)
- H-H bond, s – s, “head on”
- verlap yields sigma bond
- H-F bond, s-p, “head on”
- verlap yields sigma bond
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Think about methane – CH4 2s22p2 overlapping with 1s1
How is that possible?
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Make “new” atomic orbitals that are combinations of the “old” orbitals. We call these “hybrids”
- ne 2s + three 2p’s = four sp3
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- Describe the “new locations” of the N valence
electrons we use to describe bonding in NH3 according to VB theory.
- A. A pair of electrons in the 2s orbital and 3 sp2 orbitals,
each singly occupied.
- B. Four sp3 orbitals, each singly occupied.
- C. Four sp3 orbitals, three singly occupied and one with a
pair of electrons.
- D. Five sp3 orbitals, each singly occupied.
Poll: Clicker Questions
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NEW HYBRIDIZED ORBITALS ARE DEGENERATE!
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EXPLAIN BONDING FOR AMMONIA
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Use hybridization to explain the trigonal planar arrangement: for example BF3
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Use hybridization to explain the trigonal planar arrangement: for example BF3
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When one s and two p oribitals are mixed to form a set of three sp2 orbitals, one p orbital remains unchanged and is perpendicular to the plane of the hybrid orbitals.
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USE VB THEORY TO EXPLAIN BONDING IN ETHENE
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VB multiple bond
- Ethene has a C = C
double bond
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LABEL THE SIGMA AND PI BONDS
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USE VB THEORY TO PREDICT BONDING IN ETHYNE
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USE VB THEORY TO PREDICT BONDING IN ETHYNE
When one s orbital and one p orbital are hybridized, a set of two sp
- rbitals oriented at 180 degrees results
two p orbitals “left over” for making pi bonds.
Examples of sp hybridization: N2, HCCH, CO2
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Hybridization of orbitals for CO2
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(a) An sp hybridized nitrogen atom (b) The σ bond in the N2 molecule (c) the two π bonds in N2 are formed
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Hybridization for expanded valence
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You can match VB with VSEPR
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The molecular shapes can be explained using Valence Bond Theory - Hybridized Orbitals. WHAT HAVE WE LEARNED TODAY?
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