VSEPR Theory PDF

# VSEPR THEORY (Valence shell electron pair repulsion theory) This theory was proposed by Gillespie and Nyholm. This theory explains the effect of electron pair repulsion on the geometry of the molecule. There are two types of electron pairs: 1. Lone pair of electron (lp) 2. Bond pair of elect...

# VSEPR THEORY (Valence shell electron pair repulsion theory) This theory was proposed by Gillespie and Nyholm. This theory explains the effect of electron pair repulsion on the geometry of the molecule. There are two types of electron pairs: 1. Lone pair of electron (lp) 2. Bond pair of electron (bp) According to VSEPR theory, - all electron pairs repel each other. This repulsion is of three types: 1. Lone pair lone pair repulsion (lp-lp) 2. Lone pair bond pair repulsion (lp-bp) 3. Bond pair bond pair repulsion (bp-bp) 2. The order of electron pair repulsion is as follows: lp-lp > lp-bp > bp-bp 3. In space, a molecule acquires that geometry which has minimum repulsion. ## Conclusion from VSEPR theory: 1. If a molecule has only bond pairs of electrons surrounding the central atom, then the geometry of the molecule will be regular. ## TABLE 1: Hybridization, Geometry, Bond Angle and Example | Hybridization | Geometry | Bond angle | Example | | --------------- | ----------- | ----------- | ----------------- | | sp | Linear | 180° | CI-Be-CI | | sp² | Trigonal | 120° | BF₃ | | sp³ | Tetrahedral | 109°28' | CH₄ | | sp³d | Trigonal Pyramidal | 120°, 90° | ClF₃ | | sp³d² | Octahedral | 90° | SF₆ | 2. If a molecule has both bond pairs and lone pairs surrounding the central atom, then the geometry of the molecule will be distorted: ## TABLE 2: Example, Hybridization, Geometry and Bond Angle | Example | Hybridization | Geometry | Bond Angle | | -------- | --------------- | ------------------ | ----------- | | CH₄ | sp³ | Tetrahedral | 109°28' | | NH₃ | sp³ | Trigonal Pyramidal | 107° | | H₂O | sp³ | Inverted V | 104.5° | 3. The bond angle decreases as the electronegativity of the bonded atom increases: P / \ I I 102° Br / \ P P Br 101.5° P / \ Cl Cl 101° 4. The bond angle decreases as the electronegativity of the central atom decreases: H₂O 104.5° H₂S 93° H₂Se 91° 5. The repulsion between multiple bonds is higher than the repulsion between single bonds: F / \ F-B-C \ / CI CI 120° minimum repulsion O=C / \ CI CI less than 120° 6. The bond length increases with an increase in the number of lone pairs of electrons present in the group: CI(a) / \ CI-P-CI \ / Cl(a) CI(e) 2.01 A° 2.04 A° CI(e) # NH3 - The N atom is sp³ hybridized: 2 N(7) - 15² 2s² 2p³ 111 sp³ - NH₃ has one lone pair and three bond pairs, so there are two types of repulsion: 1. lp-bp repulsion 2. bp-bp repulsion - The lp-bp repulsion is stronger than the bp-bp repulsion, which causes NH3 to have trigonal pyramidal geometry instead of tetrahedral geometry and the bond angle changes from 109°28' to 107°. # H₂O - The O atom is sp³ hybridized: 2 O(8)-15² 2s² 2p⁴ 111 sp³ - H₂O has two lone pairs and two bond pairs, so there are three types of repulsion: 1. lp-lp repulsion 2. lp-bp repulsion 3. bp-bp repulsion - The lp-lp repulsion is the strongest repulsion among these three, which causes H₂O to have a geometry of inverted V instead of tetrahedral, and the bond angle changes from 109°28' to 104.5°. # H₃O⁺ - The O atom is sp³ hybridized: 2 O(8) - 15² 2s² 2p⁴ 111 sp³ - H₃O⁺ has one lone pair and three bond pairs, so there are two types of repulsion: 1. lp-bp repulsion 2. bp-bp repulsion - The lp-bp repulsion is stronger than the bp-bp repulsion, which causes H₃O⁺ to have a geometry of trigonal pyramidal instead of tetrahedral, and the bond angle changes from 109°28' to 107°. # SF₄ - The S atom is sp³d hybridized: 2 S(16) - 15² 2s²2p⁶ 3s²3p⁴ 3d⁰ 1111 Ground state 2 S(16) - 15² 2s²2p⁶ 3s²3p³ 3d¹ 1L 111 1 sp³d hybridization - SF₄ has four bond pairs and one lone pair, so its geometry is see-saw. ## CIF₃ - The Cl atom is sp³d hybridized: 2 Cl(17) - 15² 2s² 2p⁶ 3s² 3p⁵ 3d⁰ 11111 G.S. 2 Cl(17) - 15² 2s² 2p⁶ 3s² 3p⁴ 3d¹ 11111 sp³d hybridization - CIF₃ has one lone pair of electrons, so its geometry is T-shaped. # ICl₂^- - The I atom is sp³d hybridized: I (53) = [Kr]36 4s² 4d¹⁰ 5s² 5p⁵ 5d⁰ I^- = [Kr]36 4s² 5s² 5p⁶ 5d¹ 1L 11111 sp³d hybridization - Although ICl₂^- has one lone pair of electrons and its hybridization is sp³d, it's not a trigonal pyramidal; it is a linear geometry because of the change due to lone pair of electrons.