Section 5.3—Molecules in 3D

1. Section 5.3—Molecules in 3D

2. 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

3. Valence Shell Electron Pair Repulsion Theory (VSEPR Theory) Valence Shell Electron Pair Repulsion 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

4. 2 bonds, no lone pairs Linear Indicates a bond going away from you Trigonal planar 3 bonds, no lone pairs Indicates a bond coming out at you What shapes do molecules form?

5. 4 bonds, no lone pairs Tetrahedron Trigonal bipyramidal 5 bonds, no lone pairs What shapes do molecules form?

6. 6 bonds, no lone pairs Octahedron What shapes do molecules form?

7. 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!

8. 2 bonds, 1 lone pair Bent Trigonal pyramidal 3 bonds, 1 lone pair What shapes do molecules form?

9. 2 bonds, 2 lone pairs Bent What shapes do molecules form?

10. Lone Pairs take up more space • Lone pairs aren’t “controlled” by a nucleus (positive charge) on both sides, but only on one side. • This means they “spread out” more than a bonding pair. • They distort the angle of the molecule’s bonds away from the lone pair.

11. C 109.5° O 105° Example of angle distortion

12. Cl-1 Na+1 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.