Molecular Geometry

1
Molecular Geometry
2
Bonding

• Covalent bonds occur when atoms are at an ideal
  distance from one another.
• At this distance attractive forces predominate
  repulsive forces.
• Too close the atoms repel each other. Too far
  away they do not attract

3
Bonding
4
Polarity of Polyatomic Molecules

• Recall polar covalent bonds
• For molecules with more than one covalent bond,
  polarity depends on individual bonds and shapes
  of molecules.
• Considering HCl, the molecule is polar because of
  the shape and electronegativity differences.

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Polarity of Polyatomic Molecules

• Consider CO2
• VESPR model signifies linear molecular shape
• C-O bond is polar
• CO2 molecule nonpolar
• Overall molecular polarity is the vector sum of
  individual dipoles

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Polarity of Polyatomic Molecules

• Consider H2O
• We know it is a polar molecule
• H-O bonds are polar
• VESPR model predicts tetrahedral bent molecular
  shape
• Vector of polarity proves overall polar molecule

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Polarity of Polyatomic Molecules

• Predict if CCl4 and CHCl3 are polar.

8
Covalent Bonding and Orbital Overlap

• When covalent bonds occur we say the orbitals
  overlap.

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Multiple Bonds

• So far we have considered only s bonds.
• In a s bond the e- density is concentrated about
  the nuclear axis can occur with p or s orbital.
• In a multiple bond overlap within the p orbital
  occurs perpendicular to the nuclear axis
• The said perpindicular overlap of p orbitals
  produces a p bond

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Multiple Bonds

• Consider ethene 1 s, 1 p

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Delocalized e-

• e- localized when e- are associated w/ p and s
  bonds keeping them with 2 atoms.
• Delocalized e- can be associated w/ many atoms.
  Associated with resonance structures.
• Benzene

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Delocalized e-

• In benzene, neither of the two Lewis resonance
  structures are correct.
• The p e- are spread throughout the entire
  molecule giving the molecule incredible
  stability.

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Molecular Orbital Theory

• The theory assigns the electrons in a molecule to
  a series of orbitals that belong to the molecule
  as a whole.
• relate them to the probability of finding
  electrons in certain regions of a molecule.

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Molecular Orbital Theory

• Whenever two atomic orbitals overlap, two
  molecular orbitals form.
• The lower energy MO concentrates e- density
  between the nuclei is the bonding molecular
  orbital.
• The higher energy MO has little e- density
  between nuclei is the antibonding molecular
  orbital, signified by a

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Molecular Orbital Theory

• If the e- density is centered about the nucleus
  it is a s molecular orbital
• Often represented in energy level diagrams, note
  s1s lower energy that s1s

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Molecular Orbital Theory

• If electrons are not placed in the s1s orbital
  they must be placed in s1s
• Take theoretical molecule He2

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Molecular Orbital Theory

• Bond Order ½ (if bonding e- - of antibonding
  e-)
• Bond order relates to the stability of covalent
  bonds
• Bond order of 0 represents no bonds
• 1 represents single, 2 represents double 3
  represents triple