Presentation on theme: "Valence Shell Electron Pair Repulsion Theory"— Presentation transcript:
1Valence Shell Electron Pair Repulsion Theory VSEPRValence Shell Electron Pair Repulsion Theory
2Vocabulary:“domain”= any electron pair, or any double or triple bond is considered one domain.“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
32 domains on central atom LINEAR2 domainsboth are bonding pairsThey push each other to opposite sides of center (180 apart).BeCl2
43 domains on central atom TRIGONAL PLANAR3 domainsall are bonding pairsThey push each other apart equally at 120 degrees.GaF3
53 domains on central atom BENT3 domains:2 are bonding pairs1 is a lone pairThe 2 bonding pairs are pushed apart by 3rd pair (not seen)SnF2
6NOTE: The geometry around the central atom is trigonal planar. The molecular shape is bent.SnF2
74 domains on central atom TETRAHEDRAL4 domainsEach repels the other equally - not the expected 90.Think in 3D.CH4
84 e- pairs on central atom TRIGONAL PYRAMIDAL4 domains3 bonding pairs1 lone pairThe thicker, lone pair forces the others a little bit closer together (~107.3)NH3
9Tetrahedral vs. Trigonal pyramidal Tetrahedral geometry around the central atomTetrahedral Molecular ShapeTetrahedral geometry around the central atomTrigonal Pyramidal Molecular Shape
10Tetrahedral vs. Trigonal pyramidal On the right, the 4th 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?
114 domains on central atom, con’t BENT4 domains2 bonding pairs2 lone pairsThe bonds are forced together still closer (104.5) by the 2 thick unshared pairs.H2O
12Comparing the 2 “bents”… Both bent molecules are affected by unshared pairs – 1 pair on the left, 2 on the right.
13Other Molecular Geometry 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!
145 e- pairs on central atom TRIGONAL BIPYRAMIDAL5 shared pairsThree pairs are found in one plane (“equator”) 120 apart; the other two pairs are at the “poles,” 180 apart, 90 from the “equator.”PCl5
155 e- pairs on central atom SEE-SAW4 shared pairs & unshared pairOne of the equator pairs is unshared & pushes the other 2 together.The 2 poles are pushed slightly together.SF4
165 e- pairs on central atom T-SHAPED3 shared & 2 unshared pairs2 of the 3 equator pairs are unshared.All 3 remaining pairs are pushed together.ClF3
175 e- pairs on central atom LINEAR2 shared & 3 unshared pairsAll 3 equator pairs are unshared. The 2 remaining pairs are forced to the poles.XeF2
185 e- pairs on central atom 4 shared, 1 unshared5 shared, 0 unshared3 shared, 2 unshared2 shared, 3 unshared
196 e- pairs on central atom OCTAHEDRAL6 shared pairsEach pair repels the others equally.All angles = 90Now, if one of these pairs was unshared …SF6
206 e- pairs on central atom SQUARE PYRAMIDAL5 shared pairs & unshared pair4 shared pairs in one plane; the 5th pair at the pyramid’s top.If the pair at the top was unshared …IF5
216 e- pairs on central atom SQUARE PLANAR4 shared & 2 unshared pairsThe 4 shared pairs are in the same plane; the 2 unshared pairs are 90 from them.XeF4
226 e- pairs on central atom 6 shared, 0 unshared5 shared, 1 unshared4 shared, 2 unshared
23Steps for using VSEPR: Draw a Lewis Dot Structure. Predict the geometry around the central atom.Predict the molecular shape.… also, we can try and predict the angles between atoms.
24All e- pairs push each other as far apart as possible. Shared (bonding) pairs are “stretched” between two atoms that want them.“Longer & Thinner”Unshared (non-bonding) pairs are not “stretched.”“Shorter & Thicker”
25Electron Pair Repulsion 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 space2 bonding pairs (both thin) require the least space & repel each other the smallest distance (angle).