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VSEPR Theory Good


Katey Parker

on 28 February 2013

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Transcript of VSEPR Theory Good

Valence Shell Electron Pair Repulsion 1. Sum valence electrons 2. Form bonds between atoms using electrons 3. Arrange the remaining electrons to fulfill the octet rule VSEPR Rules (Except for H's Duet) H ● ● What is it? How do you use it? You can use the set of VSEPR rules
to predict the shape of a molecule VSEPR Theory What are the rules? What are its uses? How does it work? The geometry of an atom is determined by the repulsion of electrons The less repulsion there is the more stable the molecule is To minimize repulsion, electron pairs try to occupy positions that maximize the distance between them X A I X I A X X I I ( 90° ( 180° These elecron pairs are 90°apart These pairs are 180°apart, so they are farther away from each other, making this structure more stable than the 90°structure The type of electron pair also helps determine geometry Lone pairs are not shared and lie close to the central atom Bonded pairs are shared between atoms and are pulled away from the central atom, reducing repulsion A A X ● ● ● ● Lone Pairs VS Bonded Pairs Thus bonding pairs have less repulsion than lone pairs The strength of the repulsion between two adjacent pairs decides the bond angle A ● ● X X ● ● ● ● ● ● ( Adjacent bonded pairs have the lowest repulsion ( Adjacent bonded pair and a lone pair have average repulsion Adjacent lone pairs have highest repulsion ( Luckily there is a set of rules we can use to determine these structures (Its not really an average, its just somewhere in between the highest and the lowest) Lewis Structure Rules 1. Draw the Lewis Structure 2. Count the regions of high electron density (electron pairs) around the central atom (double bonds, triple bonds, and unpaired electrons each count as one region) 3. Identify the most stable arrangement of the high electron energy regions (linear, trigonal planar, tetrahedral, trigonal bipyramidal, and octahedral - we'll get to these later) 4. Arrange the position of the atoms around the central atom by the types of electron pairs present 5. Identify the molecular structure by the placement of the atoms around the central atom Exceptions to the VSEPR Rules 1. Transition metals - lack of one pairs in the valence orbital and interation between ligands and core D electrons results in a different geometry than VSEPR predicts
2. Group 2 Halides - they're bent rather than linear, possibly, because the interaction of ligands with core electrons polarizes the atom and shifts the structure
3. Some AX E and AX E molecules 2 2 6 AX 2 Linear Trigonal Planar AX 3 Tetrahedral AX 4 Molecular Geometry Trigonal Pyramid AX E 3 Bent or V shaped AX E 2 2 T-shaped AX E 3 2 Trigonal Bipyramidal AX 5 Importance # 1 Understanding the shape of the molecule can reveal physical and chemical properties Importance # 2 Understanding the shape of a molecule can reveal how it will interact with other molecules Importance # 3 Specifically in biology, the shape of a molecule is crucial in enzyme considering that an enzyme catalyzes reactions by binding substrates that fit into the shape of the active site Thank you for watching our Prezi on VSEPR Theory Katey Parker
Joanna Kim Octahedral AX AX E AX E 4 4 6 Seesaw Linear AX E 3 2 Square Pyramidal AX E 5 Square Planar 2 Ex: BeCl Ex: CH Ex: BF Ex: ClF Ex: H O Ex:NH Ex: PCl Ex: SF Ex: SF Ex: XeF Ex: BrF Ex: XeF 4 2 3 4 3 5 3 2 4 6 5 2
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