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45 Cards in this Set
- Front
- Back
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What is Quatum Chemistry |
The Physics of very small objects e.g. microscopic objects. |
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Classical Mechanics |
Physics of motion |
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Properties of Quantum and Classical Mechanics . |
!: Classical Mechanics : Objects that are large, heavy. Subatomic particles 2. Quantum : very light 3. Clas. Mec : Properties can change by small amount -continous 4. Only certain allowed values for changes [Energy, movement e,g,]: Quantized 5. CM : Newton's Equations 6.QM: Schrödinger's Equations - Out of the Newton's Equation one obtains a Trajectory. This gives us the exact position of a particle . Whereas a Wave functions gives us the Probability of a Particle at a specific Point in time. -no Exactness
7: |
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Blackbody Radiation? |
When heated up, it emits radiation with a specifc Spectrum. |
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Max Planck Equation for Quantized Energy |
E= nhv |
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Planck's Constant |
h = 6,626* 10^-34 J |
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Infrared Spectroscopy |
Absorption of Infrared Radiation brings about molecular Vibrations within molecules. Atom size and length varies, therefore th frequence at which a bon infrared radiation absorbs varies over a broad spectrum of bond types |
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Two modes of Vibration ? |
1.Stretching 2.Bending |
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Do two disparate Compounds have the same IR spectrum? |
No.. Due to the Presence on different Bond length, Angle and initial Vibration |
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Units of Spectroscopy |
C= Frequency *wavelength E = hv ; Planck's Constant *frequency |
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Wavenumbers |
1/wavelength =1/cm |
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Concept of Vibrational Spectroscopy |
Two Balls separated by a string would oscillate[harmonic] if stretched and released . The frequency of the vibrations depends on the strength of the string [=bond] and the mass of the balls [=atoms] The energy is quantised, which means that only certain enrgy levels are allowed according to this formula En =[n+1/2] hv where n= 0,1,2,3, etc The total Energy is given by the sum of the Potential Energies of the compressed and extended positions.However Bonds in reality don't oscillate harmonically |
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When atoms come close to one another what hapens? |
They exert a strong repulsive force and beyond a certain separation distance the bond breaks. |
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Quantisation of Eenergy causes what? |
Unequal spacing of energy levels |
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What type of molecules absorb IR radiation? |
Dipol Molecules e.g.HCl however molecules like H2 are unresponsive. |
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For nonlinear Molecules like Pentane, there is number of Vibrations allowed, what is it? |
this number is given by [3N-6] N is the number of atoms in the molecule Water , for instance, has 3 modes of vibration
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Why does CO2 produce only two Peaks in the Spectrum? |
First, It is a linear molecule. This is because the symmetric stretch does not have a dipole and the two bending vibrations [in plane and out of plane] are degenerate [of equal energy], so they cancel out. |
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The strength or Intensity of the Absorption is dependent on what? |
the change of the dipole moment occuring during the Vibration
Ifthere is no dipole moment, the radiation cannot interact with the vibration, and thus no absorption |
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Absorption of single bonds to Hydrogen occur aroung what wavenumbers? |
4000-2500cm^-1 |
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For electronegative Atoms like Oxygen and Nitrogen what happens ? |
the peak would be broadened due to inter and intra molecular hydrogen bonding
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The absorptions of triple bonds occur around? |
2500-2000cm^-1 |
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Absorption of double Bonds ? |
2000-1500 cm^-1 |
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When do the values of Absorption [ in wavenumber ] fall ? |
when the bonds become more conjugated [i.e having the single bond character] |
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Carbonyl Bonds ? |
Strongly affected by the mesomeric effect of the bonded carbony carbon |
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The lower the energy difference between two states ? |
the lower the difference in Population |
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Rotational Energies depends on what? |
The moments of Inertia A combination of Mass and distance between atoms |
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Why do we use the reduced mass? |
Because we can't really pinpoint the center mass of both atoms. |
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Reduced Mass is only applicable to ? |
diatomic Molecules |
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Rigid ? |
Does not distort under Moments of stress |
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When the transmission is small? |
the sample is doig alot of absorbing |
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Moment of Inertia |
Is the resistance of a rotating body to a change in the rotational motion on an axis |
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linear Velocity |
radius * angular velocity |
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Rigid Rotor |
here the Bond length doesnt change |
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Quantised Rotational Energy Levels |
Ej = J [J+1] hbar²/2I
in joules J = 0,1,2,3,... are possible rotational quantum numbers
there is no 0 rotational energy because it means it is not rotating .
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For every value of Jj there is a ? |
wave function and energy level
Fj = Ej/hc = J[J+1]h/8pi² I c = BJ [J+1] in cm^-1
Fj = rotational term |
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B? |
Rotational Constant =h/8pi²Ic |
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In Spectroscopy we are ? |
exciting a molecule from one energy level to another |
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When does absorption occur? |
When the frequence of the radiation matches the difference in energy between the two energy levels |
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F is a function of ? |
J |
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What does increasing j really mean? |
As we increase J, the energy increases. Simulatneously the Rotation goes faster |
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What does J = 0 mean? |
This means the rotational energy is = 0 ; no rotation |
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Rotational Selection Rule |
+/- 1 only transition between adjacent levels is allowed |
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microwave inactive molecules are? |
Homonuclear diatomic molecules symmetric linear molecules |
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Rotational term for the transition |
deltaE/hc =v=F[j+1]- F[J] =2B[J+1] |
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What is the Pattern of the Bond length during transition to higher energy levels or higher rotations |
The Bond lengths vary and are not the same |
