Molecular Shapes: True shapes of molecules Lewis Structure (2D) Molecular Shape (3D) 2

Valence Shell Electron Pair Repulsion Theory VSEPR Theory Valence Shell Electron Pair Repulsion Theory Main ideas – Electron pairs have repulsions of each other, but they have to be positioned as requested Need to position these electron pairs as far as possible As to minimize repulsions between electron pairs Determines the shape of 3D molecule 1 Lone Pair = 2 Left Over e- Look up: 1) Bonding vs Left over electron pairs on Different Atoms 2) Bonding vs Left over electron pairs on Central Atom 3) Left over electrons Pairs around Central Atom

Steps for Predicting Molecular Structures using VSEPR Model Draw the Lewis Structure for the molecule. Count the electron pairs and arrange them in the way that minimize repulsions (put the pairs as far apart as possible). Determine the positions of the atoms from the way the electrons pairs are shared. Determine the name of the molecular structure from the positions of the atoms. Must Show 3-D shape by using and

Be Careful When Drawing Molecular Shapes No Charge and No [ ] around the shape Only Draw the Lone Pair @ Central Atom  Don’t draw the Left Over e- around other atoms Bend when having Lone Pair @ central atom When Bending, Lone Pair stay on the top, Bonds stay on the bottom. More Lone Pair @ Central Atom  Bend More

Left Over e- (Lone Pair) Lone Pair: Valence e- pair that is not involved in bonding Linear, Trigonal Planar, and Tetrahedral have NO lone pair around the central atoms

Left Over e- (Lone Pair) around Central Atoms What about if there are lone pair around the central atom? REMEMBER: Lone Pair (LP) also take up space!!! repel each other repel bonded pairs Use as lone pair@ central atom instead of electron pairs.

5 Molecular Shapes A) Linear (2 kinds) B) Trigonal Planar C) Tetrahedral D) Trigonal Pyramid E) Bent (2 kinds) Total Atoms = Central Atom + Bonded Atom ? Lone Pair TA = CA + BA ? LP

A) Linear (2 kinds) Linear 2 Linear 1 2 TA = 0 CA + 2 BA, 0 LP  angle = 180 degrees  angle = 180 degrees Linear 2 Linear 1

4 TA = 1 CA + 3 BA, 0 LP  angle = 120 degrees B) Trigonal Planar 4 TA = 1 CA + 3 BA, 0 LP  angle = 120 degrees

Need to draw and C) Tetrahedral 5 TA = 1 CA + 4 BA, 0 LP Molecular Shapes C) Tetrahedral 5 TA = 1 CA + 4 BA, 0 LP angle = 109.5 degrees Need to draw and

Need to draw and D) Trigonal Pyramidal 4 TA = 1 CA + 3 BA, 1 LP  angle = 107.2 degrees Remember, lone pairs take up space! (Use Oval) 107.2 Need to draw and

3 TA = 1 CA + 2 BA, 1 LP  angle = 119.2 – 120 degrees E) Bent (2 kinds) 3 TA = 1 CA + 2 BA, 1 LP  angle = 119.2 – 120 degrees 3 TA = 1 CA + 2 BA, 2 LP  angle = 105 degrees Bent 1 Bent 2 Need to draw and