VSEPR THEORY Valence Shell Electron Pair Repulsion Theory

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VSEPR THEORY (Valence Shell Electron Pair Repulsion Theory) Adapted by Mr. M. McIsaac Carleton North High School, Bristol, NB From Mr. James Montgomery SCH4U Grade 12 Chemistry Sir John A. MacDonald Secondary School Waterloo, ON sjam.wrdsb.on.ca/records/Lesson14 vsepr .ppt

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What Is The VSEPR Theory? VSEPR Theory is utilized to foresee the states of atoms. Consider fortified sets (shared) or solitary sets (nonbonded, unshared) of e - 's as adversely charged mists that repulse each other. To accomplish the most stable condition the mists must be as far separated as would be prudent in 3-D, in this manner diminishing repugnance. The measure of aversion can be requested: LP-LP > LP-BP > BP-BP keeping in mind the end goal to decide the shape, the Lewis graph must be drawn first.

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2 Bond Pairs/Electron Groups Molecules that exclusive have 2 holding sets on the focal particle will have a LINEAR SHAPE with a bond edge of 180 ° e.g. BeF 2 , CO 2 , CS 2 General Formula: AX 2 Central particle A from gathering 2; 2 BP 0 LP

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Example BeF 2

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3 Bond Pairs/Electron Groups Molecules that have 3 holding sets on the focal iota will have a TRIGONAL PLANAR SHAPE with bond edges of 120 °. e.g. BF 3 , BH 3 General Formula: AX 3 Central particle A from gathering 13; 3 BP 0 LP

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Example BF 3

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4 Bonding Pairs/Electron Groups If the focal molecule is put at the focal point of a circle, than each of the four sets of electrons will involve a position to be as far separated as could be allowed. This will bring about the electron sets being at the sides of a customary tetrahedron, thusly these particles are said to have a TETRAHEDRAL SHAPE. The edge between every bond will be 109.5 ° e.g. CCl 4 , CH 4 , SiH 4 General Formula: AX 4 Central iota A from gathering 14; 4 BP 0 LP

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Example CCl 4

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3 Bonding Pairs & 1 Non-holding Pair Four sets of electrons will dependably orchestrate themselves tetrahedrally around the focal molecule. The state of the particle is dictated by the game plan of the molecules not the electrons. Therefore such atoms will have a TRIGONAL PYRAMIDAL shape. Because of the shock, a non-holding electron match requires more space than a holding pair, the points in these atoms are 107 ° not 109.5° as in the tetrahedral particles. e.g. NH 3 , PCl 3 General Formula: AX 3 E Central iota A from gathering 15; 3 BP 1 LP

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Example NH 3

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2 Bonding Pairs & 2 Non-holding Pairs The four sets of electrons will be organized tetrahedrally however since just 2 sets are holding electrons, the encompassing iotas are at 2 corners of the tetrahedron. Subsequently these particles will have a V-SHAPE or BENT. The repugnance between the non-holding sets will bring about a bond edge of 104.5 °. For every combine of non-holding electrons, the bond edge diminishes by 2.5° e.g. H 2 O, H 2 S, OCl 2 General Formula: AX 2 E 2 Central particle A from gathering 16; 2 BP 2 LP

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Example H 2 O

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Things to Remember keeping in mind the end goal to foresee the state of an atom you should draw the Lewis Dot Diagram for the atom, decide the quantity of holding and non-holding electron combines and contrast this and the outline you have been given (the shapes must be retained). While deciding the state of a particle with various bonds, regard the numerous bonds as though they were single bonds (i.e. one holding pair)

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5 Molecular Shapes From Single Bonds

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