molecular geometry notes
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Molecular Geometry Notes. February 3, 2014. You will be able to describe the molecular geometry of a molecule. Correct HW 6B A note on nomenclature Notes Cool video of the day: Check out THIS ionic crystal lattice!! . Binary Nomenclature. - PowerPoint PPT PresentationTRANSCRIPT
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Molecular Geometry Notes
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February 3, 2014
• You will be able to describe the molecular geometry of a molecule.
• Correct HW 6B• A note on nomenclature• Notes
• Cool video of the day: Check out THIS ionic crystal lattice!!
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Binary Nomenclature
• First element by name (with prefix, ONLY if there is more than one atom)
• Second element as an “-ide”, with prefix
• Does not work for molecules with more than 2 atoms
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• CO• NO• SF2
• SO2
• NO2
• NCl3
• CCl4
• H2O
• N2F6
• N2O5
Carbon monoxideNitrogen monoxideSulfur difluorideSulfur dioxideNitrogen dioxideNitrogen triclorideCarbon tetrachlorideDihydrogen monoxideDinitrogen hexafluorideDinitrogen pentoxide
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Molecular Geometry
• Applies to any Lewis diagram. (Involved in covalent bonding)
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VSEPR Theory
• Valence Shell Electron Pair Repulsion• Each bonding group or lone pair of electrons
spreads out as far as possible from every other bonding group or lone pair of electrons.
• Think 3D!
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Electron Pair vs. Molecular Geometry
• Electron pair geometry describes both bonds AND lone pairs located around the central atom.
• Molecular geometry describes only the bonds located around the central atom.
• Molecular geometry is a subset of electron pair geometry.
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Practice
How many bonding groups are around the central atom? 4
How many lone pairs around the central atom? 0
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Practice
How many bonding groups are around the central atom? 3
How many lone pairs are around the central atom? 1
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Practice
How many bonding groups are around the central atom? 3
How many lone pairs are around the central atom? 0
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Practice
How many bonding groups are around the central atom? 2
How many lone pairs are around the central atom? 0
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Electron Pair Geometry: Overview (Not in notes)
• The shape of the molecule including both bonds and lone pairs
• Linear– 2 e- groups from central atom
• Trigonal Planar – 3 e- groups from center
• Tetrahedral – 4 e- groups from center
Any of these lobes (electron groups) can be either lone pairs or covalent bonds
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REMEMBER
• ELECTRON PAIR GEOMETRY and MOLECULAR GEOMETRY are not the same thing.– EPG describes all electron groups (including lone
pairs)– MG describes only bonding groups
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2 Electron Groups
• Electron pair geometry: Linear
– 2 bonding groups– 0 lone pairs– Molecular geometry: Linear
– Example: CO2
• 2 bonding groups• 0 lone pairs
Double and triple bonds count as just ONE bonding group!!!
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3 Electron Groups
• Electron pair geometry: Trigonal Planar
– 3 bonding groups– 0 lone pairs– Molecular geometry: Trigonal planar
– Example: NO3- Double and triple
bonds count as just ONE bonding group
This Lewis structure also shows the molecular shape (trigonal planar).
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3 Electron Groups
• Electron pair geometry: Trigonal Planar
– 2 bonding groups– 1 lone pair– Molecular geometry: Bent
– Example: NO2- Double and triple
bonds count as just ONE bonding group
Lone pair is one of the three electron groups around the central atom
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4 Electron Groups
• Electron pair geometry: Tetrahedral – 4 bonding– 0 lone pairs– Molecular geometry: Tetrahedral
– Example: CH4
This Lewis structure does NOT show the tetrahedral molecular shape. It DOES show the four electron groups.
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4 Electron Groups
• Electron pair geometry: Tetrahedral – 3 bonding– 1 lone pair– Molecular geometry: Trigonal Pyramidal
– Example: NH3
This Lewis structure does NOT show the molecular shape. It DOES show the four electron groups.
Lone pair is one of the four electron groups around the central atom
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4 Electron Groups
• Electron pair geometry: Tetrahedral – 2 bonding groups– 2 lone pairs– Molecular geometry: Bent/Angular
– Example: H2OThis Lewis structure shows both the molecular shape and the four electron groups
Lone pairs are two of the four electron groups around the central atom
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Molecular Geometry: Overview
• The shape of the molecule including just bonds between atoms.
• 2 e- groups from central atom: – If 2 bonds/0 lone pairs: Linear
• 3 e- groups from central atom: – 3 bonds/0 lone pairs: Trigonal planar– 2 bonds/1 lone pair: Bent
• 4 e- groups from central atom: – 4 bonds/0 lone pairs: Tetrahedral– 3 bonds/1 lone pair: Trigonal pyramidal– 2 bonds/2 lone pairs: Bent
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Sketches of Molecular Geometry
• Sketches (on homework, quizzes, and tests) should show the shape of the molecule in three dimensions:
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Exceptions to the Octet Rule(SF6, BrF5, XeF4, IF7 )
(Beyond the scope of this class)