General Chemistry
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Draw an atomic-level representation of an amorphous solid.
Draw an atomic-level representation of a crystalline material.
Identify the coordination numbers of the blue atoms, red atoms, and yellow atoms in the following crystal structure.
Crystalline solids are classified into four main classes. List them and provide an example for each.
Thermal contraction is a decrease in a material's volume when its temperature decreases.
What happens to the dimensions of the unit cell and its density?
Consider the two packing patterns below:
Identify the type of two-dimensional lattice.
Identify the angle between the lattice vectors.
Consider the drawings below representing two polymers:
Identify which is expected to have a lower boiling point?
Consider the following sections of molecules below:
Identify which is expected to conduct electricity better.
Consider the arrangement of the lattice below where the orange spheres are the cations and the green spheres are the anions.
Which structure is more stable?
Draw the 2D unit cell for each structure below:
Identify the correct statement regarding crystalline and amorphous solids
X-rays with wavelength 71.1 pm were diffracted in second order by rubidium, revealing an interplanar spacing of 152.3 pm. Calculate the diffraction angle. Second-order diffraction corresponds to n = 2.
X-rays with wavelength 154.2 pm were diffracted in first order by platinum at an angle of 40.67º. Calculate the interplanar spacing in platinum.
In an X-ray diffraction experiment, germanium crystal can be used instead of silicon crystal because Si and Ge have the same bonding properties and you will essentially achieve the same results. Is this assumption correct?
In an X-ray diffraction analysis, it was found that X-ray from NaCl radiation source has a wavelength of 194 pm. The selected crystalline plane diffracted the radiation at an angle of 25.9 degrees. Assuming that this is second-order diffraction (n = 2) and using the Bragg equation, calculate the spacing between the adjacent crystal planes.
The energy given off by a mole of iron atoms by Kα transition is 6.15x105 kJ. Calculate the wavelength of X-rays in Å given off by the Kα transition.
The maximum reflection of a UV light with a 315 nm incident on the surface of a crystal produced an angle of u = 26.4°
Calculate the separation between layers of atoms in the crystal assuming n = 1.
Identify which of the following is expected to have no band gap.
Indicate if the following are n-type or p-type semiconductors
(i) Ge doped with As
(ii) Si doped with B
(iii) Sn doped with Sb
Identify the semiconductor and electrical insulator from the given energy-level diagrams.
Describe the reasons why semiconductors have greater electrical conductivity.
Give the definition for Band gap
Energy-level graphs for two distinct LEDs are shown in diagrams (i) and (ii). The one LED produces yellow light, and the other LED produces violet light. Which produces yellow and which violet light? Explain.
The electron populations of the bands of MO energy levels for an element is illustrated in the graph below:
Determine the band gap, conduction band, and valence band.
The electron populations of the bands of MO energy levels for four distinct materials are illustrated in the graphs below:
As the temperature increases, indicate whether the conductivity of each material increases or decreases.
Lanthanum calcium manganate (La0.7Ca0.3MnO3) is a magnetic semiconductor that exhibits colossal magnetoresistance, meaning its electrical resistance changes dramatically in the presence of an applied magnetic field. How many d electrons are there on each La3+ ion in this material? The 4d orbital is lower in energy than the 6s orbital.
Indium antimonide (InSb) is used in thermal imaging sensors and infrared detectors. InSb has a band gap of 16.4 kJ/mol. Is InSb expected to be an insulator, conductor, or semiconductor? With what group 4A element, do you expect InSb to be isoelectronic with?
Considering the electronegativities of the elements, rank the following extrinsic (doped) semiconductors from the least conductive to the most conductive.
In0.25Ga0.75P, In0.70Ga0.30P, In0.50Ga0.50P
How is an LED (light emitting diode) different from a photovoltaic cell?
Rank these substances in descending order based on their electrical conductivities.
Si doped with P, Ag, NaCl, Al, Ge
True or false. The behavior of a superconductor, a material that totally loses all electrical resistance below its superconducting transition temperature, is shown in the graph below.
The illustration below shows the molecular orbital diagram of a doped semiconductor. Which of the following elements could be a dopant if the semiconductor is germanium, and does the diagram represent n-type or p-type doping?
The electron population of molecular orbitals for various compounds is shown in the graphs below. Which of the following diagrams corresponds to aluminum oxide, gallium arsenide, and mercury?
Consider 3 vials containing semiconductor nanocrystals, each embedded in a polymer matrix. The samples containing different average sizes of particles exhibit photoluminescence by irridiation of UV light. Each vial emits a different color of light, blue, green, and yellow. Identify which vial has the smallest average particle size of the semiconductor.
Consider a theoretical crystal in a shape of a cube with a 0.70 mm edge length and density of 9.21 g/cm3. The spacing between energy levels may be approximated by dividing the range of energies by the number of atoms in the crystal assuming that the spacing between levels is equal. If the range of energy levels of the crystal is 2.5x10-17 J and the molar mass is 53.69 g/mol, calculate the average spacing in J between energy levels.
Consider a large crystal of ZnSe are illuminated with ultraviolet light. Would appropriately sized ZnSe quantum dots be able to emit green light considering that it has a band gap of 2.58 eV.
Consider a large crystal of ZnSe are illuminated with ultraviolet light. Would appropriately sized ZnSe quantum dots be able to emit yellow light considering that it has a band gap of 2.58 eV.
Identify the color is the emitted light if large crystals of ZnSe are illuminated with ultraviolet light considering that it has a band gap of 2.58 eV.
Does Ge absorb a greater or lesser portion of the solar spectrum than InSb?
Calculate the wavelength of light of a photon that would have the energy equal to the band gap of indium antimonide.
The following illustration shows the electronic structure of a doped semiconductor. Which of the following statements is true?
Identify which element would be the best candidate to dope InP and replace some In atoms to make an n-type semiconductor.
Choose between the semiconductors AlAs and AlSb which has a larger band gap.
Identify the insulator and semiconductor based on the given image of the two solids
The band gap in germanium is 0.67 eV. Would a photon of orange light with a frequency of 4.84×1014 Hz possess sufficient energy to promote an electron from the valence band to the conduction band?
Silicon is doped with boron. Determine if this substance is an n-type or a p-type semiconductor.
The band gap of a solid is 5.9 eV at 273.15 K. Classify the following as a metal, an insulator, or a semiconductor.
A sodium crystal has a mass of 21.5 g. Calculate the number of molecular orbitals present in the conduction band of the sodium crystal.
Among the following solids below, which would have the widest band gap?
a. Ge(s)
b. Si(s)
c. Ti(s)
Silicon and germanium are the only two elements that are practically useful semiconductors. However, compound semiconductors that are made from two or more elements are also used. Some examples are CdSe, CdS, GaP, and GaAs. The semiconductor industry classifies these compound semiconductors into 'II–VI' and 'III–V' materials. Identify which compounds are in each category.
Silicon and germanium are the only two elements that are practically useful semiconductors. However, compound semiconductors that are made from two or more elements are also used. Some examples are CdSe, CdS, GaP, and GaAs.
What is the basis for pairing up these elements? Base your observation on its similarities to Si and Ge.
Identify which of the following elements is NOT a conductor or semi-conductor
i. Ti
ii. Cu
iii. Ge
iv. N
v. Si