Molecules in 3D

Bonds repel each other Bonds are electrons. Electrons are negatively charged Negative charges repel other negative charges Bonds repel each other Molecules arrange themselves in 3-D so that the bonds are as far apart as possible

Valence Shell Electron Pair Repulsion Theory Valence Shell Electron Pair Repulsion Theory (VSEPR Theory) Outer shell of electrons involved in bonding Bonds are made of electron pairs Those electron pairs repel each other Attempts to explain behavior This theory (that bonds repel each other because they’re like charges) attempts to explain why molecules form the shapes they form

Lone Pairs Lone pairs are electrons, too…they must be taken into account when determining molecule shape since they repel the other bonds as well. But only take into account lone pairs around the CENTRAL atom, not the outside atoms!

Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs ShapeExamples Covalent Structure Make this table, you will fill it out throughout the activity. You will learn ten shapes today.

What shapes do molecules form? Linear 2 bonds, no lone pairs Ex: BeCl 2 Trigonal planar 3 bonds, no lone pairs Ex: BF 3 Indicates a bond coming out at you Indicates a bond going away from you

What shapes do molecules form? Tetrahedral 4 bonds, no lone pairs Ex: CH 4, SiCl 4 Trigonal pyramidal 3 bonds, 1 lone pairs Ex: NH 3, PCl 3

What shapes do molecules form? Trigonal bipyramidal 5 bonds, no lone pairs Ex: PCl 5 Bent 2 bonds, 2 lone pairs Ex: H 2 O, H 2 S, SCl 2

What shapes do molecules form? T-shaped 3 bonds, 2 lone pairs Ex: ClF 3, BrF 3 Seesaw 4 bonds, 1 lone pairs Ex: SF 4

What shapes do molecules form? Octahedron 6 bonds, no lone pairs Ex: SF 6, WCl 5 Square pyramidal 5 bonds, 1 lone pairs Ex: ClF 5, BrF 5

Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs ShapeExamples Linear Trigonal planar Tetrahedral Pyramidal Bent BeCl 2 BF 3 CH 4, SiCl 4 NH 3, PCl 3 H 2 O, H 2 S, SCl 2 -Be- B C N : O : : Covalent Structure

Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs ShapeExamples Trigonal bypramidal T-shaped Seesaw Square Pyramidal Bent PCl 5 ClF 3, BrF 3 SF 4 ClF 5, BrF 5 SF 6 B P Covalent Structure P : : : S Cl :

109.5° C 105° O Example of angle distortion

Ionic Compound structures Ionic compounds are made of positive and negative ions. They pack together so that the like-charge repulsions are minimized while the opposite-charge attractions are enhanced. Na +1 Cl -1

Part 1—Molecules with no lone pairs 5 large and 20 small marshmallows, 20 toothpicks In this activity, the atoms will be the marshmallows and the bonds (electrons) will be the toothpicks. The toothpicks will connect the “atoms,” which want to be as far away from each other as possible. For this exercise, the central atom (the large one) will be called A and the outside atoms (the smaller ones) will be called X. There will be no lone pairs in these models! Construct: AX 2, AX 3, AX 4, AX 5, AX 6

Part 2-Molecules with lone pairs A lone pair is a pair of electrons that is not being shared by two atoms. This case would be represented in the models by a toothpick sticking out of the central atom without an outside atom bonded to it. These molecules are based on the molecules you already built. Construct: AX 2 with one lone pair, AX 2 with two lone pairs, AX 3 with one lone pair, AX 3 with two lone pairs AX 4 with one lone pair, AX 5 with one lone pair