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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.
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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!!
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
CO • NO • SF2 • SO2 • NO2 • NCl3 • CCl4 • H2O • N2F6 • N2O5 Carbon monoxide Nitrogen monoxide Sulfur difluoride Sulfur dioxide Nitrogen dioxide Nitrogen tricloride Carbon tetrachloride Dihydrogen monoxide Dinitrogen hexafluoride Dinitrogenpentoxide
Molecular Geometry • Applies to any Lewisdiagram. (Involved in covalent bonding)
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!
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.
Practice • How many bonding groups are around the central atom? • 4 • How many lone pairs around the central atom? • 0
Practice • How many bonding groups are around the central atom? • 3 • How many lone pairs are around the central atom? • 1
Practice • How many bonding groups are around the central atom? • 3 • How many lone pairs are around the central atom? • 0
Practice • How many bonding groups are around the central atom? • 2 • How many lone pairs are around the central atom? • 0
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
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
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!!!
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).
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
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.
4 Electron Groups • Electron pair geometry: Tetrahedral • 3bonding • 1lone pair • Molecular geometry:Trigonal Pyramidal • Example: NH3 Lone pair is one of the four electron groups around the central atom This Lewis structure does NOT show the molecular shape. It DOES show the four electron groups.
4 Electron Groups • Electron pair geometry: Tetrahedral • 2 bonding groups • 2 lone pairs • Molecular geometry:Bent/Angular • Example: H2O Lone pairs are two of the four electron groups around the central atom This Lewis structure shows both the molecular shape and the four electron groups
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
Sketches of Molecular Geometry • Sketches (on homework, quizzes, and tests) should show the shape of the molecule in three dimensions:
Exceptions to the Octet Rule(SF6, BrF5, XeF4, IF7 )(Beyond the scope of this class)