Homework 3: Chapters 8-9
Assigned 1 February 2006; Due 6 February 2006; Quiz on 8 February 2006
Optical Atomic Spectroscopy (Chapter 8)
Atomic Absorption (Chapter 9)
1.Consider the figures below. What is the energy difference between the 3 p levels for Na and Mg+? Which has the larger difference? The wavelengths are in angstroms.
Use E=hc/ and calculate E for each 4s->3p transition. The difference is the difference in the 3p energy levels.
hc=3E8 m/s * 6.626E-34 Js=1.99E-25 m J
E=hc(1/1-1/2)
For Na
E=1.99E-25(1/11383E-10-1/11404E-10)=3.22E-22 J
For Mg+
E=1.99E-25(1/2929E-10-1/2936E-10)=1.62E-21 J
The Mg+ has the larger energy difference.
2.Provide the electronic energy symbol for V
The electronic configuration is 3d34s2
S is from the 3 electrons in the d orbital
3 (1/2) =3/2
3/2*2+1 = 4
The unpaired electrons occupy the d orbital, so the order is 2,1,0,-1,-2. With 3 electrons L= 2+1+0 =3 =F
Since the orbital is less than half filled J=3-3/2 =3/2
The term symbol is 4F3/2
3.What is the term symbol of Mo
4d55s1
six electrons, 6/2*2+1=7
L=0=S
6/2+0=3
7S3
4.What can broaden lines in spectroscopy?
Doppler effect
1Atomic movement during measurement.
Uncertainty principle
1vt from the uncertainty principle shows that frequency and time cannot both be exactly known. This error in the wavelength measurement is around 1E-4 Å
Thermal effect
2described by Boltzmann’s distribution. Occupation of higher orbitals.
5.What is needed to send a sample into an AA device? How is it achieved?
The sample must be volatilized. The difference methods are below.
6.What is the ratio of excited state (3p) to ground state (3s) Na atoms at the following temperatures?
300 K
1200 K
2000 K
3000 K
Use Boltzmann’s equation
1)
For Na 3s to 3p
substitute the temperatures and solve for
T (K) /300 / 1.33E-35
1200 / 4.36E-09
2000 / 1.49E-05
3000 / 8.75E-04
7.What are the different zones in a flame?
Primary combustion zone
Blue luminescence due to C2 and CH
Thermal equilibrium not reached in primary zone
Interzonal region
Central part of flame
High concentration of free atoms
Used for spectroscopy
Secondary combustion region
Convert elements to oxides
Disperse sample to air
8.What lamp is needed for AA?
The lamp is specific for the element to be examined. The lamp is based on compound examined. For example a Na lamp is used to examine Na.
9.What are some possible interferences in AA?
a.Overlap of sample spectra
i.Not very common due to narrow line widths. If it does occurs select different transition
b.Scattering
i.Formation of oxides the scatter light in the flame
c.Chemical Interference
i.More common than spectral interference. Formation of compounds with low volatility. Additives can remove volatile compounds