Molecules E&R Chapter 12. Outline Bonding 12-1 –Ionic 12-2 –Covalent 12-3 Molecular Excitations...
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Transcript of Molecules E&R Chapter 12. Outline Bonding 12-1 –Ionic 12-2 –Covalent 12-3 Molecular Excitations...
Molecules
E&R Chapter 12
Outline
• Bonding 12-1– Ionic 12-2– Covalent 12-3
• Molecular Excitations 12-4– Rotation 12-5– Vibration 12-6– Electronic– Electronic + Vibration + Rotation 12-7
Bondinghttp://hyperphysics.phy-astr.gsu.edu/hbase/chemical/chemcon.html#c1
R Nave, Georgia State Univ
Chemical Bondinghttp://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bondcon.html#c1
R Nave, Georgia State Univ
Ionic Bonds
RNave, GSU at http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html#c4
Ionic Bonds
Ionic Bonding
RNave, Georgia State Univ at hyperphysics.phy-astr.gsu.edu/hbase/molecule
Ionic Bonding
a.u. = atomic energy unit = 2*(13.6eV) Brandsen&Joachim
E&R
Covalent Bonds
RNave, GSU at http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html#c4
Covalent Bonding SYM ASYMspatial spin
ASYM SYMspatial spin
Covalent Bonding
Stot = 1
not really parallel, but spin-symmetric
not really anti, but spin-asym
Stot = 0
Covalent Bonding
Bransden&Joachin
Ionic vs Covalent Bond Properties
• Ionic Characteristics– Crystalline solids
– High melting & boiling point
– Conduct electricity when melted
– Many soluble in water, but not in non-polar liquids
• Covalent Characteristics– Gases, liquids, non-
crystalline solids– Low melting & boiling point
– Poor conductors in all phases
– Many soluble in non-polar liquids but not water
Rotational Spectra
)1(22
1
2
1~
222 rr
IIIKErot
R
rotational A.M.moment of inertia
Rotation
Rotation
Rotational Spectra
Ocean Optics: Nitrogen N2
~ 0.3 eV
~ 0.4 eV
Vibration
Molecule“Spring Const”
( N/m )
HF 970
HCl 480
HBr 410
Hi 320
CO 1860
NO 1530
Vibration (in an Electronic state)
Electronic + Vibration
Electronic + Vibration + Rotation
2.656 eV2.550 eV
electronic excitation gap
vibrational excitation gaps
Electronic + Vibration + Rotation
2.656 eV
electronic excitation gap
vibrational excitation gaps
Vibrational WellVibrational Well
depth ~ 0.063 eV
Electronic, Vibration, RotationElectronic ~ optical & UV
~ 1 – 3 eV
Vibration ~ IR ~ 10ths of eV
Rotation ~ microwave ~ 1000ths of eV
Electronic + Vibration + Rotation
2.656 eV2.550 eV
electronic excitation gap
vibrational excitation gaps
** + Vibration + Rotation
IN A DIATOMIC MOLECULEbecause a photon has one unit of
angular momentum,the rotational quantum number
must change(vib is not angular motion)
r = 0 not allowed
** + Vibration + Rotation
Ocean Optics: Nitrogen N2
~ 0.3 eV
~ 0.4 eV
Some Molecular ConstantsMolecule Equilibrium
Distance
Ro (Å)
Dissociation NRG
Do (eV)
Vibrational freq
v a (cm-1)
Moment of Inertia
Bb (cm-1)
H2+ 1.06 2.65 2297 29.8
H2 0.742 4.48 4395 60.8
O2 1.21 5.08 1580 1.45
N2 1.09 9.75 2360 2.01
CO 1.13 9.60 2170 1.93
NO 1.15 5.3 1904 1.70
HCl 1.28 4.43 2990 10.6
NaCl 2.36 4.22 365 0.190
Notes: a) vibrational frequency in table is given as f / c b) moment of inertia in table is given as hbar2/(2I) / hc
Fluorescence
absorb at one wavelength, emit at another
Phosphorescence
tunneling slows the decay process