CHAPTER 9CHAPTER 9
AP/HONORS CHEMISTRYAP/HONORS CHEMISTRY
MOLECULAR GEOMETRYMOLECULAR GEOMETRY VSEPR - valence-shell electron pair repulsionVSEPR - valence-shell electron pair repulsion IDEAL GEOMETRIESIDEAL GEOMETRIES Type geometry bond angle Type geometry bond angle ABAB22 (2 e- pairs) Linear 180 (2 e- pairs) Linear 180oo example on board example on board ABAB33 (3 e- pairs) Triangular 120 (3 e- pairs) Triangular 120oo example on board example on board
PlanarPlanar ABAB44 (4 e- pairs) Tetrahedral 109.5 (4 e- pairs) Tetrahedral 109.5oo example on board example on board ABAB55(5 e- pairs) Trigonal 120(5 e- pairs) Trigonal 120oo & 180 & 180o o example on board example on board
bipyramidal bipyramidal ABAB66(6 e- pairs) Octahedral 90(6 e- pairs) Octahedral 90oo example on board example on board
EFFECT OF UNPAIRED EFFECT OF UNPAIRED ELECTRONSELECTRONS
Type geometry bond angle Type geometry bond angle ABAB22E (2 e- pairs, Bent example on boardE (2 e- pairs, Bent example on board
1 lone pair)1 lone pair) ABAB22EE22 (2 e- pairs, Bent 105 (2 e- pairs, Bent 105oo example on board example on board
2 lone pairs)2 lone pairs) ABAB33E (3 e- pairs, Triangular 107E (3 e- pairs, Triangular 107oo example on board example on board
1 lone pair) pyramidal1 lone pair) pyramidal the electron pair geometry approximately the same as that the electron pair geometry approximately the same as that
observed when only single bonds existobserved when only single bonds exist
CONTINUEDCONTINUED
the molecular geometry is quite different the molecular geometry is quite different with lone pairs. Why?with lone pairs. Why?
lone pairs take up more space than when lone pairs take up more space than when bondedbonded
consider NHconsider NH33 it has a electronic pair it has a electronic pair
geometry of tetrahedral but the angle is geometry of tetrahedral but the angle is 107107oo
the water molecule is nonlinear because of the water molecule is nonlinear because of lone pairs 105lone pairs 105oo
OTHER LONE PAIR GEOMETRIESOTHER LONE PAIR GEOMETRIESABAB44E see-saw SFE see-saw SF44
ABAB33EE22 T-shaped ClF T-shaped ClF33
ABAB22EE22 linear XeF linear XeF22
ABAB55E square pyramidal BrFE square pyramidal BrF55
ABAB44EE22 square planar XeF square planar XeF44
when dealing with geometries multiple bonds when dealing with geometries multiple bonds behave like single bondsbehave like single bonds
CONTINUEDCONTINUED
the geometry depends upon how many the geometry depends upon how many terminal atoms the central atom has terminal atoms the central atom has around it and the number of unshared around it and the number of unshared electronselectrons
the VSEPR model can be extended to the VSEPR model can be extended to molecules which do not have a single molecules which do not have a single central atom. Ccentral atom. C22HH22 and C and C22HH44
POLARITY OF MOLECULESPOLARITY OF MOLECULES
PolarPolar large (not large enough to form ionic bonds) large (not large enough to form ionic bonds)
electronegative differenceelectronegative differenceunequal share of the electronsunequal share of the electrons
nonpolar equal sharingnonpolar equal sharing the degree of polarity is measured by its dipole the degree of polarity is measured by its dipole
moment moment ππ = Qr, Q = charge at either end, r = distance = Qr, Q = charge at either end, r = distance 1 debye = 3.33 x 101 debye = 3.33 x 10-30-30 coulomb-meters H-Cl coulomb-meters H-Cl
1.03D bond length 1.36 Ǻ1.03D bond length 1.36 Ǻ
CONTINUEDCONTINUED is it easy to determine whether a diatomic molecule is it easy to determine whether a diatomic molecule
is polar. Why?is polar. Why? check if the elements are the same or differentcheck if the elements are the same or different if a molecule contains more than two atoms, we if a molecule contains more than two atoms, we
must decide whether the whole molecule is polar or must decide whether the whole molecule is polar or nonpolarnonpolar
the are two criteria for determining the polarity of a the are two criteria for determining the polarity of a molecule: bond polarity and molecular geometry molecule: bond polarity and molecular geometry
ATOMIC ORBITALSATOMIC ORBITALS Sigma bonds Sigma bonds σσ
single lobe where the electron density is single lobe where the electron density is concentrated in the region directly between two concentrated in the region directly between two bonded atomsbonded atoms
pi bond pi bond ππ this orbital has two lobes one above the bond axis this orbital has two lobes one above the bond axis
and one below. The electron density is zeroand one below. The electron density is zero all single bonds are sigma bonds and any other all single bonds are sigma bonds and any other
bond in a double or triple bond will be pi bondsbond in a double or triple bond will be pi bonds on boardon board hybrid orbitals on boardhybrid orbitals on board
DELOCALIZE BONDINGDELOCALIZE BONDING
The bonds are given to all atoms i.e. benzene The bonds are given to all atoms i.e. benzene on board makes it stable (aromaticity)on board makes it stable (aromaticity)
magnetism - molecules with one or more magnetism - molecules with one or more paired electrons are attracted to a magnetic paired electrons are attracted to a magnetic fieldfield
the more unpaired electrons, stronger the more unpaired electrons, stronger attraction- paramagnetismattraction- paramagnetism
with no unpaired electrons, weak repulsion - with no unpaired electrons, weak repulsion - dimagnetismdimagnetism
Top Related