By: Deanna Ross, Minjia Wu, Michael
Kshatri, Brandon Walker, and Taylor
Svete
• Lewis Structure
• Do not indicate the shapes of molecules
• Show the number and types of bonds between atoms
• Bond Angles
• Angles made by lines joining the nuclei of the atoms in the molecule
• Determines the overall shape
• ABn
• N=2, linear or bent
• N=3, trigonal planar, trigonal pyramidal, or t-shaped
• The shape of any of these types of molecules can be defrived from one
of five basic geometric structures: linear, trigonal planar, tetrahedral,
trigonal bipyramidal, and octahedral
• Predicting shpaes is determined by VESPR model
• What type of shape is CO₂? What is the bond angle?
• What type of shape is SO₂?
• Bonding Pair- defines region where electrons will likely be
found. Such a region=electron domain.
• Ex. NH3 has three electron domains
• VSEPR Model based on domains being negatively charged
• Best arrangement of a given number of electron domains is the
one that minimizes repulsion among them.
• The one with the least has the least amount of lone pairs
• Electron Domain Geometry- the arrangement of electron
domains about the central atom or ion.
• Can take many shapes
Number of Electron Electron Domain
Domains
Geometry
Predicted Bond
Angles (in
degrees)
2
Linear
180
3
Trigonal Planar
120
4
Tetrahedral
109.5
5
Trigonal
bipyramidal
120 or 90
6
Octahedral
90
• Molecular Geometry- arrangement of only the atoms in a
molecule or ion.
• Nonbonding pairs not used in molecular geometry.
• Examples:
• CO2 has 2 bonding domains. Linear
• NO2 is bent, 2 bonding domains, one lone pair
• Refer to page 347 and 350 for all shapes
• Nonbonding pairs take up more space and thus exerts a
greater repulsive force on adjacent electron domains and
compresses angles.
• With expanded valence shells, equatorial exerts more power
than axial.
• For larger molecules, split into different parts around central
atom and define each region’s information using VSEPR
• Draw the Lewis Dot Structure BF3. State
•
•
•
•
The number of electron domains
The number of bonding domains
The number of nonbonding domains
Its Molecular Geometry (shape)
• Bond Polarity- Measure of how equally the electrons in a bond
are shared between the two atoms of the bond
• “As the difference of electro-negativity between 2 atoms
increases so does the bond polarity”
• Dipole Movement- quantitative measure of the amount of
charge separation in the molecule
• Dipole moments have significant effect on physical and chemical
properties
• “The Dipole moment depends on both the polarities of the
individual bonds and the generosity of the molecule”
• Bond Dipole- Dipole moment that is due only due only to the 2
element in that bond
• Bond Dipole and dipole moments are vector quantities
• Overall Dipole moment is the vector sum of the bond dipoles.
• 9. 4
• VSEPR does not explain why bonds exist between atoms
• Valence Bond Theory: the marriage of Louis’s notion of electron-pair
bonds and the idea of atomic orbitals leads to a model of chemical
bonding
• 9. 5
• Hybrid orbitals-when the atomic orbitals on an atom mix to form new
orbitals
• Hybridization- process of mixing orbitals
• 9.6
• Sigma bonds- the line joining the two nuclei that passes through the
middle overlap region
• Pi bond- what the sideways overlap of p orbitals produce
Pi molecular orbitals:
2p orbitals that overlap
sideways and therefore
concentrate electron
density above and
below the internuclear
axis (the line connecting
the nuclei)
Paramagnetism:
The more unpaired
electrons in a species,
the stronger the
attraction will be.
Diamagnetism:
Substances with no
paired electrons are weakly
repelled from a magnetic
field.