Introduction to spectroscopy, energy and bonding Autumn semester Flashcards

1
Q

What are the equations relating wave length, frequency and speed of light

A

c = λv

c = speed of light (m/s)
λ = wavelength (nm)
v = frequency (1/cm)

E = hv

E= energy (joules)
h = plancks constant
v = frequency

E= hc/λ

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2
Q

What is rotational spectroscopy?

A

Gaseous molecules can rotate and it is quantised, the absorbed wavelengths correspond to microwaves and infrared regions of electromagnetic spectrum.

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3
Q

What is the gross and specific selection rule for rotational spectroscopy?

A

gross > must posses a permanent dipole
Specific selection > ΔJ = + or - 1

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4
Q

How to calculate allowed rotational energy levels?

A

Ej = hBJ(J+1)

E = energy of rotational quantum number (joules)
h = planks contant (joules/seconds)
B = rotational consent (1/seconds)
J = rotational quantum number

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5
Q

How do you calculate the rotational constant (B)?

A

B = h/8π ^2I
I = moment of inertia (Kg m^2)

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6
Q

How do you calculate moment of inertia (I)?

A

I = ur(o)^2
u = reduced mass (Kg)
R(o) = bond length (m) need to convert any measurement to m normal need to or form nm to m x10-9

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7
Q

How do you calculate reduced mass of atoms?

A
  1. work out the mass of the atoms in Kg by Mr divided by 1000 (converts it to Kg mol-1) / avocadros number
  2. then substitute into
    U = m1 x m2 / m1+ m2
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8
Q

What is the centrifugal distortion coefficient?

A

Although in calculations bond length is treated as a constant there slight changes which accounted for by the centrifugal distortion coefficient

Ej = hBJ(J+1) - DJ^2(J+1)^2

D = centrifugal distortion coefficient

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9
Q

What is vibrational spectroscopy?

A

This is the molecular vibrations of the individual chemical bond, it is quantised and correspond to the Ir on the electromagnetic spectrum.

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10
Q

What is the gross and specific selection rule for vibrational spectroscopy?

A

gross > must be a change in the dipole moment, thus must have a permanent dipole
specific selection > ΔV + or - 1

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11
Q

How do you calculate vibrational energy levels?

A

Ev = (V +1/2) hv

V= vibrational energy level
v = frequency

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12
Q

How do you calculate the force constant for vibrational energy?

A

v = 1/2π (k/u)^1/2

v = frequency of vibration
k = force constant (stiffness) (kg/s^2)

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13
Q

How do you calculate potential energy in vibration energy?

A

Epe = 1/2kx^2

k = spring constant
x = amount of extension,displacment

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14
Q

How do you calculate anharmonic vibrations?

A

EV = (V+1/2)hv - Xe (V +1/2)^2hv

Xe = anharmonic constant

anharmonic oscillation means that ΔV + or - 1 is exactly true

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15
Q

How do you calculate the vibrational modes of freedom for a linear and non-linear molecule?

A

Linear = (3N -5) Modes
non linear = (3N-6) Modes

N = number of atoms

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16
Q

What is electronic spectroscopy?

A

This is the process of a beam of light being passed through an atom exciting an electron to a higher energy state resulting in colour. It corresponds to the uv/vis spectrum.

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17
Q

What is the beer-lamberts law?

A

This allows us to calculate the molar absorption coefficient and wavelength for different absorbance points and whether an electronic state is forbidden.

A = εcl

ε = molar absorption coeffeinct (dm^3 / mol cm)
c = concentration (mol dm^-3)
l = path length (cm)

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18
Q

how does the molar absorption coefficient say whether a electronic state is forbidden of not?

A

ε is negative its strongly forbidden
ε is 10-100 weakly allowed
ε is 500+ its strongly allowed

19
Q

What is a chromophore?

A

The part of the molecule that is responsible for the absorption of light, it is normally a conjugated system. With the longer the conjugated system the longer the wave length and the smaller the energy of absorption.

20
Q

What is NMR spectroscopy?

A

Nuclear magnetic resonance Spectroscopy uses radio-frequencies to cause transitions between the Zeeman energy levels of nuclei in a magnetic field.m

21
Q

how do you calculate the energy change between the ground state to exited state of an nucleus?

A

ΔE = hyB(o) / 2π = hv

h = placks
y = magnetic ratio
B(o) = strength of the magnetic field

22
Q

What impacts the the chemical shift?

A

Electrons is the surrounding bonds shield the nucleus from the full effect of the magnetic field given a range of chemical shifts. The more shielding present the lower the chemical shift.
- electron withdrawing groups remove electron density and increase chemical shifts meaning higher energy of radio waves absorbed
- electron donating groups increase shielding.

23
Q

What is spin-spin coupling?

A

pin coupling between NMR active nuclei that are not chemically identical. Different spin states interact through chemical bonds in a molecule to give rise to this coupling.
n +1 rules gives us the number of surrindign hydrogens.

24
Q

What impacts the intensity if peaks?

A

Mainly useful for proton NMR, the size of the peaks in the NMR spectra can give information concerning the number of nuclei that gave rise to that peak. This is done by measuring the peak’s area using integration

25
Q

How do you calculate bond order?

A

Bond order = 1/2(number of bonding electrons - number of anti-bonding electrons)
if the bond order is 0 the molecule won’t bond/exist.

26
Q

Whats boyles gas law?

A

At constant temperature and a fixed amount of gas the volume of the gas will reduce proportional to an increase in pressure.

27
Q

What is Charles gas law?

A

At a constant pressure, the volume of a fixed amount of gas will increase with increasing temperature.

28
Q

What is Avogadro’s gas law?

A

Equal volumes of gas at a consent temperature and pressure contains equal numbers of molecules.

29
Q

What is the ideal gas equation?

A

pV = nRT

p = pressure (pa)
V = volume (m^3)
R = ideal gas constant
T = temperature (K)

30
Q

What is Daltons law of partial pressures?

A

The pressure exerted by a mixture of gases is the sum of the partial pressure of the gases.

31
Q

How is partial pressure calculated?

A

P(A) = mole fraction of A x total pressure

mole fraction (A) = number of gaseous moles of A/ total number of gaseous moles

32
Q

What is kinetic molecule theory with gases?

A

This describes the gases behaviour in terms of molecules that are in constant random motion in every direction. Evidence is
- flow (fills a volume)
- thermal expansion
- brownian motion (collision with Microparticles create random motion)
- diffusion

33
Q

How can you calculate the kinetic energy of. a gas molecule?

A

for a singel molecule
E(kE) = 1/2 ms^2

m = mass (kg)
s = molecular speeds (m/s)

For per molecule
E(kE) = 1/2 mc^2

34
Q

How do you calculate the average molecular speed of a gas?

A

for mean kinetic energy and pV use molecular speeds
C = (s1^2 +s2^2…/N)^1/2

for effusion, colliosn frequency and mean free path use mean speed
C = s1 + s2…/N

35
Q

How to calculate the average molecular speed?

A

C = (3RT/M)^1/2

C = root mean square speed of molecules (m/s)
R = gas constant
T = temperature (K)
M = molar mass (kg/mol)

36
Q

How can you plot the difference in modular speeds?

A

At any instant molecule will move at different speeds it distributed by plotting speed (s) on the x axis with number of molecules on the y axis.

37
Q

What affects molecular speeds?

A
  • temperature (increase temp increase kinetic energy)
  • mass (as mass increases molecule moves slower)
38
Q

What is Grahams law of effusion?

A

At a given temperature and gas pressure the rate of effusion is inversely proportional to the square root of the molar mass.

Rate od effusion = 1/M^1/2

Rate of effusion A/rate of effusion B = (M(B) /M(A))^1/2

39
Q

How does the hard sphere model show bonding?

A

When two molecules collide they can only get as close as their van Der Waals radii will permit for the orientation of that collision

width of molecule = 2 x van Der Waals radius (2x1.5A)
Length of molecule = 2 x van Der Waals radius + bond length

40
Q

How do you calculate the collision cross-section?

A

σ = π (2r)^2 = π d^2

41
Q

What is collision frequency?

A

The mean number of collisions that a molecule experiences per seconds (Z)

Z = Square root of 2 x N (A) x (Cσ)(p/RT)

N = number of molecules

42
Q

What is mean free path?

A

The average difference a molecule travels between collision at a given temperature and pressure.

λ = average speed (C) / average time between collisions (Z)

43
Q

What is the Van Der Waals equations for gases?

A

(p + a(n/v)^2)(V-nb0 = nRT

44
Q
A