1. CHAPTER 9 AP/HONORS CHEMISTRY

2. MOLECULAR GEOMETRY VSEPR - valence-shell electron pair repulsion VSEPR - valence-shell electron pair repulsion IDEAL GEOMETRIES IDEAL GEOMETRIES Type geometry bond angle Type geometry bond angle AB 2 (2 e- pairs) Linear 180 o example on board AB 2 (2 e- pairs) Linear 180 o example on board AB 3 (3 e- pairs) Triangular 120 o example on board AB 3 (3 e- pairs) Triangular 120 o example on board Planar Planar AB 4 (4 e- pairs) Tetrahedral 109.5 o example on board AB 4 (4 e- pairs) Tetrahedral 109.5 o example on board AB 5 (5 e- pairs) Trigonal 120 o & 180 o example on board AB 5 (5 e- pairs) Trigonal 120 o & 180 o example on board bipyramidal bipyramidal AB 6 (6 e- pairs) Octahedral 90 o example on board AB 6 (6 e- pairs) Octahedral 90 o example on board

3. EFFECT OF UNPAIRED ELECTRONS Type geometry bond angle Type geometry bond angle AB 2 E (2 e- pairs, Bent example on board AB 2 E (2 e- pairs, Bent example on board 1 lone pair) 1 lone pair) AB 2 E 2 (2 e- pairs, Bent 105 o example on board AB 2 E 2 (2 e- pairs, Bent 105 o example on board 2 lone pairs) 2 lone pairs) AB 3 E (3 e- pairs, Triangular 107 o example on board AB 3 E (3 e- pairs, Triangular 107 o example on board 1 lone pair) pyramidal 1 lone pair) pyramidal the electron pair geometry approximately the same as that observed when only single bonds exist the electron pair geometry approximately the same as that observed when only single bonds exist

4. CONTINUED the molecular geometry is quite different with lone pairs. Why? the molecular geometry is quite different with lone pairs. Why? lone pairs take up more space than when bonded lone pairs take up more space than when bonded consider NH 3 it has a electronic pair geometry of tetrahedral but the angle is 107 o consider NH 3 it has a electronic pair geometry of tetrahedral but the angle is 107 o the water molecule is nonlinear because of lone pairs 105 o the water molecule is nonlinear because of lone pairs 105 o

5. OTHER LONE PAIR GEOMETRIES AB 4 E see-saw SF 4 AB 4 E see-saw SF 4 AB 3 E 2 T-shaped ClF 3 AB 3 E 2 T-shaped ClF 3 AB 2 E 2 linear XeF 2 AB 2 E 2 linear XeF 2 AB 5 E square pyramidal BrF 5 AB 5 E square pyramidal BrF 5 AB 4 E 2 square planar XeF 4 AB 4 E 2 square planar XeF 4 when dealing with geometries multiple bonds behave like single bonds when dealing with geometries multiple bonds behave like single bonds

6. CONTINUED the geometry depends upon how many terminal atoms the central atom has around it and the number of unshared electrons the geometry depends upon how many terminal atoms the central atom has around it and the number of unshared electrons the VSEPR model can be extended to molecules which do not have a single central atom. C 2 H 2 and C 2 H 4 the VSEPR model can be extended to molecules which do not have a single central atom. C 2 H 2 and C 2 H 4

7. POLARITY OF MOLECULES Polar Polar large (not large enough to form ionic bonds) electronegative difference large (not large enough to form ionic bonds) electronegative difference unequal share of the electrons unequal share of the electrons nonpolar equal sharing nonpolar equal sharing the degree of polarity is measured by its dipole moment the degree of polarity is measured by its dipole moment π = Qr, Q = charge at either end, r = distance π = Qr, Q = charge at either end, r = distance 1 debye = 3.33 x 10 -30 coulomb-meters H-Cl 1.03D bond length 1.36 Ǻ 1 debye = 3.33 x 10 -30 coulomb-meters H-Cl 1.03D bond length 1.36 Ǻ

8. CONTINUED is it easy to determine whether a diatomic molecule is polar. Why? is it easy to determine whether a diatomic molecule is polar. Why? check if the elements are the same or different check if the elements are the same or different if a molecule contains more than two atoms, we must decide whether the whole molecule is polar or nonpolar if a molecule contains more than two atoms, we must decide whether the whole molecule is polar or nonpolar the are two criteria for determining the polarity of a molecule: bond polarity and molecular geometry the are two criteria for determining the polarity of a molecule: bond polarity and molecular geometry

9. ATOMIC ORBITALS Sigma bonds σ Sigma bonds σ single lobe where the electron density is concentrated in the region directly between two bonded atoms single lobe where the electron density is concentrated in the region directly between two bonded atoms pi bond π pi bond π this orbital has two lobes one above the bond axis and one below. The electron density is zero this orbital has two lobes one above the bond axis and one below. The electron density is zero all single bonds are sigma bonds and any other bond in a double or triple bond will be pi bonds all single bonds are sigma bonds and any other bond in a double or triple bond will be pi bonds on board on board hybrid orbitals on board hybrid orbitals on board

10. DELOCALIZE BONDING The bonds are given to all atoms i.e. benzene on board makes it stable (aromaticity) The bonds are given to all atoms i.e. benzene on board makes it stable (aromaticity) magnetism - molecules with one or more paired electrons are attracted to a magnetic field magnetism - molecules with one or more paired electrons are attracted to a magnetic field the more unpaired electrons, stronger attraction- paramagnetism the more unpaired electrons, stronger attraction- paramagnetism with no unpaired electrons, weak repulsion - dimagnetism with no unpaired electrons, weak repulsion - dimagnetism