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V alence S hell E lectron P air R epulsion Theory

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lone pair = non-bonding pair = unshared pair = any electron pair that is not involved in bonding bonding pair = shared pair = any electron pair that is involved in bonding domain = any electron pair, or any single, double, or triple bond is considered one domain

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VSEPR theory assumes that the shape of a molecule is determined by the repulsion of electron pairs.

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These are the electron-domain geometries for two through six electron domains around a central atom.

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» The Electron Geometry is often NOT the shape of the molecule, however. » The Molecular Geometry is defined by the positions of only the atoms/bonds in the molecules, NOT the nonbonding pairs.

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»E»Electron Geometries: Count EVERYTHING »M»Molecular Geometries: ONLY count the atoms/bonds

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o</:)---/-----<

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LINEAR » 2 domains » both are bonding pairs » They push each other to opposite sides of center (180 apart). BeCl 2

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TRIGONAL PLANAR » 3 domains » all are bonding pairs » They push each other apart equally at 120 degrees. AlF 3

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BENT » 3 domains: ˃2 are bonding pairs ˃1 is a lone pair » The 2 bonding pairs are pushed apart by 3 rd pair (not seen) SnF 2

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» The Electron Geometry around the central atom is Trigonal Planar. » The Molecular Geometry is Bent. SnF 2

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TETRAHEDRAL » 4 domains » Each repels the other equally - 109.5 - not the expected 90 . » Think in 3D. CH 4

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TRIGONAL PYRAMIDAL » 4 domains ˃3 bonding pairs ˃1 lone pair » The thicker, lone pair forces the others a little bit closer together (~107.3 ) NH 3

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Tetrahedral Electron Geometry around the central atom Tetrahedral Molecular Geometry Tetrahedral Electron Geometry around the central atom Trigonal Pyramidal Molecular Geometry

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On the right, the 4 th lone pair, is not seen as part of the actual molecule, yet affects shape. If another one of the bonding pairs on trigonal pyramidal were a lone pair, what is the result?

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BENT » 4 domains ˃2 bonding pairs ˃2 lone pairs » The bonds are forced together still closer (104.5 ) by the 2 unshared pairs. H2OH2O

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Both bent molecules are affected by unshared pairs – 1 pair on the left, 2 on the right.

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TRIGONAL BIPYRAMIDAL » 5 shared pairs » Three pairs are found in one plane (“equator”) 120 apart; the other two pairs are at the “poles,” 180 apart, 90 from the “equator.” PCl 5

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OCTAHEDRAL » 6 shared pairs » Each pair repels the others equally. » All angles = 90 SF 6

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Just for fun, let’s look at some others that we will not study in detail in this course… Note that if there are more than five domains around the central atom, it must be an exception to the octet rule!

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5 e - pairs on central atom 5 shared, 0 unshared 4 shared, 1 unshared 3 shared, 2 unshared 2 shared, 3 unshared

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6 e - pairs on central atom 6 shared, 0 unshared 5 shared, 1 unshared 4 shared, 2 unshared

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1.) Draw a Lewis Dot Structure. 2.) Find the electronic geometry around the central atom. 3.) Find the molecular shape. … also, we can try and predict the angles between atoms. USE THE ELECTRONIC GEOMETRY USE THE ELECTRONIC GEOMETRY

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» Stop Notes Here!\ o</:)----/------<

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» Shared (bonding) pairs are “stretched” between two atoms that want them. ˃“Longer & Thinner” » Unshared (non-bonding) pairs are not “stretched.” ˃“Shorter & Thicker”

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» 2 lone pairs require the most space & repel each other the most, resulting in the greatest distance (angle). » 1 lone pair (thick) & 1 bonding pair (thin) require less space » 2 bonding pairs (both thin) require the least space & repel each other the smallest distance (angle).

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SEE-SAW » 4 shared pairs & 1 unshared pair » One of the equator pairs is unshared & pushes the other 2 together. » The 2 poles are pushed slightly together. SF 4

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T-SHAPED » 3 shared & 2 unshared pairs » 2 of the 3 equator pairs are unshared. » All 3 remaining pairs are pushed together. ClF 3

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LINEAR » 2 shared & 3 unshared pairs » All 3 equator pairs are unshared. The 2 remaining pairs are forced to the poles. XeF 2

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SQUARE PYRAMIDAL » 5 shared pairs & 1 unshared pair » 4 shared pairs in one plane; the 5 th pair at the pyramid’s top. If the pair at the top was unshared … IF 5

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SQUARE PLANAR » 4 shared & 2 unshared pairs » The 4 shared pairs are in the same plane; the 2 unshared pairs are 90 from them. XeF 4

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