chapter 101 bonding and molecular structure chapter 10
TRANSCRIPT
Chapter 10 1
Bonding and Molecular Bonding and Molecular StructureStructure
Chapter 10Chapter 10
Chapter 10 2
Covalent Bonding and Orbital OverlapCovalent Bonding and Orbital Overlap
- Lewis structures and VSEPR do not explain how a bond forms.
- VSEPR predicts the shape of a molecule, but it does not explain how the molecule is put together.
- One method to explain bonding would be Valence Bond Theory:
- Bonds form when atomic orbitals on atoms overlap.- Two electrons are shared by the orbital overlap.
Chapter 10 3
Covalent Bonding and Orbital OverlapCovalent Bonding and Orbital Overlap
Chapter 10 4
Hybrid OrbitalsHybrid Orbitalsspsp Hybrid Orbitals Hybrid Orbitals- Consider BeF2
- Be has a 1s22s2 electron configuration.- There is no unpaired electron available for bonding. - We could promote and electron from the 2s orbital on Be to
the 2p orbital to get two unpaired electrons for bonding.- The F-Be-F bond angle is 180 (VSEPR theory).
- BUT the geometry is still not explained.
Chapter 10 5
Hybrid OrbitalsHybrid Orbitalsspsp Hybrid Orbitals Hybrid Orbitals- We can solve the problem by allowing the 2s and one
2p orbital on Be to mix or form two hybrid orbitals (process called hybridization).
- The hybrid orbitals come from an s and a p orbital and is called sp hybrid orbital.
Chapter 10 6
Hybrid OrbitalsHybrid Orbitalsspsp Hybrid Orbitals Hybrid Orbitals- The two sp hybrid orbitals are 180 apart.- Since only one of the Be 2p orbitals has been used in
hybridization, there are two unhybridized p orbitals remaining on Be.
Chapter 10 7
Hybrid OrbitalsHybrid OrbitalsHybrid OrbitalsHybrid Orbitals- Other hybrids can be formed by mixing additional p and/or d orbitals
Chapter 10 8
Hybrid OrbitalsHybrid Orbitals
Chapter 10 9
Hybrid OrbitalsHybrid Orbitals
Chapter 10 10
Hybrid OrbitalsHybrid OrbitalsSummarySummaryTo assign hybridization:
- draw a Lewis structure- assign the electron pair geometry using VSEPR theory- from the electron pair geometry, determine the
hybridization
Chapter 10 11
Multiple BondsMultiple Bonds -Bonds - electron density lies on the axis between the
nuclei.
-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 -bonds come from unhybridized p orbitals.
Chapter 10 12
Multiple BondsMultiple Bonds
Chapter 10 13
Multiple BondsMultiple BondsEthylene, C2H4
Chapter 10 14
Multiple BondsMultiple BondsAcetylene, C2H2
Chapter 10 15
Molecular OrbitalsMolecular Orbitals- Some aspects of bonding are not explained by Lewis
structures, VSEPR theory and hybridization. - For these molecules, we use Molecular Orbital Theory
(MO theory).- Just as electrons in atoms are found in atomic
orbitals, electrons in molecules are found in molecular orbitals.
Chapter 10 16
Molecular OrbitalsMolecular OrbitalsThe Hydrogen Molecule The Hydrogen Molecule - When two AOs overlap two MO’s form.- One molecular orbital has electron density between
nuclei (, bonding MO);- One molecular orbital has little electron density
between nuclei (*, antibonding MO).
Chapter 10 17
Molecular OrbitalsMolecular OrbitalsThe Hydrogen Molecule The Hydrogen Molecule
Chapter 10 18
Molecular OrbitalsMolecular OrbitalsThe Hydrogen Molecule The Hydrogen Molecule
Chapter 10 19
Molecular OrbitalsMolecular OrbitalsThe Hydrogen Molecule The Hydrogen Molecule
Chapter 10 20
Molecular OrbitalsMolecular OrbitalsThe Hydrogen Molecule The Hydrogen Molecule - MO diagram shows the energies and orbitals in an
MO diagram.- The total number of electrons in all atoms are placed
in the MO’s starting from lowest energy (1s) and ending when you run out of electrons.
- Note that electrons in MO’s have opposite spins.- H2 has two bonding electrons.- He2 has two bonding electrons and two antibonding
electrons.
Chapter 10 21
Molecular OrbitalsMolecular OrbitalsBond OrderBond OrderDefine Bond Order = ½(bonding electrons - antibonding electrons).
Bond order = 1 for single bond.Bond order = 2 for double bond.Bond order = 3 for triple bond.
Bond order for H2 = ½(bonding electrons - antibonding electrons) = ½(2 - 0) = 1.
Therefore, H2 has a single bond.
Bond order for He2 = ½(bonding electrons - antibonding electrons) = ½(2 - 2) = 0.
Therefore He2 is not a stable molecule.
Chapter 10 22
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
AO’s combine according to the following rules- The number of MO’s equals the number of AO’s- AO’s of similar energy combine - As overlap increases, the energy of the MO decreases
- Pauli: each MO has at most two electrons- Hund: for degenerate orbitals, each MO is first
occupied singly.
Chapter 10 23
Molecular Orbitals from 2Molecular Orbitals from 2pp Atomic Orbitals Atomic Orbitals- There are two ways in which two p orbitals overlap
- end on so that the resulting MO has electron density on the axis between nuclei ( orbital)
- sideways so that the resulting MO has electron density above and below the axis between nuclei ( orbital).
- The p-orbitals must give rise to 6 MO’s: one and two ’sone * and two *’s
- The relative energies of these and -orbitals can change.
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 24
Molecular Orbitals from 2Molecular Orbitals from 2pp Atomic Orbitals Atomic Orbitals
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 25
Electron Configurations for BElectron Configurations for B22 through Ne through Ne22
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 26
Electron Configurations for BElectron Configurations for B22 through Ne through Ne22
- For B2, C2 and N2 the 2p orbital is higher in energy
than the 2p.
- For O2, F2 and Ne2 the 2p orbital is lower in energy
than the 2p.
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 27
Electron Configurations for BElectron Configurations for B22 through Ne through Ne22
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 28
Electron Configurations for BElectron Configurations for B22 through Ne through Ne22
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 29
Electron Configurations and Molecular PropertiesElectron Configurations and Molecular PropertiesTwo types of magnetic behavior:
- Paramagnetism, unpaired electrons in molecule - Diamagnetism, no unpaired electrons in molecule
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 30
Electron Configurations and Molecular PropertiesElectron Configurations and Molecular Properties
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
Chapter 10 31
HomeworkHomework
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