Unit 12, Part II: VSEPR Theory Molecular Geometry Unit 12, Part II: VSEPR Theory Unit 12: Molecular Structure LPChem: Wz

Molecular Geometry Geometry = shapes VSEPR Theory Valence Shell Electron Pair Repulsion AKA: electrons hate each other LPChem: Wz Unit 12: Molecular Structure

VSEPR Theory mutual repulsion. The electrons interacting in molecules (valence shell electron pairs) Are REPULSED by each other. The electron pairs around the central atom orient themselves as far apart as possible– in order to minimize their mutual repulsion. LPChem: Wz Unit 12: Molecular Structure

VSEPR Shapes “Atoms bonded to the same central atom, orient themselves as far apart as possible.” The central atom in a Lewis Dot Structure could be bonded to: Only 1 other atom or… As many as ____ other atoms LPChem: Wz 6 Unit 12: Molecular Structure

VSEPR Shapes If there are 2 atoms bonded to the same central atom, what is the farthest apart they can be? LPChem: Wz Because they are repulsed by each other. The 2 atoms bonded to the center atom are trying to stay far away from each other. Unit 12: Molecular Structure

VSEPR Shapes Try it! What happens when 3 atoms are bonded to the same central atom? 4 atoms? 5? 6? (Hint: with 4, 5, or 6 secondary atoms, the molecule will NOT be flat!) LPChem: Wz Unit 12: Molecular Structure

Center atom (A) = large marshmallow Toothpicks = bonds (Use single bonds only.) Secondary atoms (B) = small marshmallow (5 large, 20 small, 20 toothpicks) Build 5 molecules: AB2 AB3 AB4 AB5 AB6 LPChem: Wz These three should NOT be flat! Unit 12: Molecular Structure

VSEPR Shapes We built: Their electron domain shapes: Linear AB2 AB3 AB4 AB5 AB6 Their electron domain shapes: Linear Trigonal Planar Tetrahedral Trigonal Bipyramidal Octahedral LPChem: Wz Unit 12: Molecular Structure

About your VSEPR notes: ABxEy form A = central atom B = bonding domains E = unshared electron pairs Bond angle: the angle between the bonds to two secondary atoms. LPChem: Wz Unit 12: Molecular Structure

VSEPR Shapes AB2: Linear 2 domains 180º Linear CS2 LPChem: Wz 180º Linear CS2 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

About your VSEPR notes: AB2: Linear 2 domains LPChem: Wz 180º Linear CS2 Electron Domain Shape and Molecular Shape are the same when there are no unbonded pairs (E). Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

About your VSEPR notes: AB2: Linear 2 domains LPChem: Wz If one end of the molecule is more electronegative than the other, it is a POLAR molecule. Molecules that are symmetrical (in 3D) are NONPOLAR. Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

About your VSEPR notes: AB2: Linear 2 domains LPChem: Wz 180º Linear CS2 Bonds only count as ONE bonding domain (B) even if they are double or triple bonds! Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

VSEPR Shapes AB1Ex : Linear 2 domains 180º LPChem: Wz 180º Linear (two points make a line) CO Polar (unless both atoms are identical) Unit 12: Molecular Structure

VSEPR Shapes AB3: Trigonal planar 3 domains 120º Trigonal planar NO3- LPChem: Wz 120º Trigonal planar NO3- Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

VSEPR Shapes AB2E: Trigonal planar 3 domains (2B +1E) <120º LPChem: Wz <120º Bent 120 SO2 Always Polar (because of the unshared pair) Unit 12: Molecular Structure

VSEPR Shapes AB4: Tetrahedral 4 domains ~109º Tetrahedral CH4 LPChem: Wz ~109º Tetrahedral CH4 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

VSEPR Shapes AB3E: Tetrahedral 4 domains (3B + 1E) <109º LPChem: Wz <109º Trigonal Pyramidal NH3 Always Polar (because of the unshared pair) Unit 12: Molecular Structure

VSEPR Shapes AB2E2: Tetrahedral 4 domains (2B + 2E) <<109º LPChem: Wz <<109º Bent 109 H2O Always Polar (because of the unshared pairs) Unit 12: Molecular Structure

AB5: Trigonal Bipyramidal VSEPR Shapes AB5: Trigonal Bipyramidal 5 domains LPChem: Wz 120º & 90º Trigonal Bipyramidal PF5 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

AB4E: Trigonal Bipyramidal VSEPR Shapes AB4E: Trigonal Bipyramidal 5 domains (4B + 1E) LPChem: Wz <120º & <90º See-saw SF4 Always Polar (because of the unshared pair) Unit 12: Molecular Structure

AB3E2: Trigonal Bipyramidal VSEPR Shapes AB3E2: Trigonal Bipyramidal 5 domains (3B + 2E) LPChem: Wz <90º T-Shaped ClF3 Always Polar (because of the unshared pairs) Unit 12: Molecular Structure

AB2E3: Trigonal Bipyramidal VSEPR Shapes AB2E3: Trigonal Bipyramidal 5 domains (2B + 3E) LPChem: Wz 180º Linear XeF2 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

VSEPR Shapes AB6: Octahedral 6 domains 90º Octahedral SF6 LPChem: Wz 90º Octahedral SF6 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

VSEPR Shapes AB5E: Octahedral 6 domains (5B + 1E) <90º LPChem: Wz <90º Square Pyramidal ClF5 Always Polar (because of the unshared pair) Unit 12: Molecular Structure

VSEPR Shapes AB4E2: Octahedral 6 domains (4B + 2E) 90º Square Planar LPChem: Wz 90º Square Planar KrF4 Nonpolar (if the secondary atoms match) Unit 12: Molecular Structure

Remember: VSEPR Theory H N Shape is defined by the CENTRAL atom. LPChem: Wz The total number of electron domains touching the CENTRAL ATOM is what determines the shape of the molecule. Electron domain: Bonded electron pair(s) OR Unshaired pair Unit 12: Molecular Structure

VSEPR Theory O S Electron domains: Bonded electron pair(s) A single bond = 1 electron domain. LPChem: Wz S O A double bond = 1 electron domain (surprise!) A triple bond? Still just 1 domain. Unshaired pair = 1 electron domain Unit 12: Molecular Structure