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Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
A point defect in crystals that does not alter the density of the relevant solid is called a "vacancy defect." In a vacancy defect, atoms are missing from their lattice positions in the crystal structure. Despite the absence of these atoms, the overall density of the crystal remains unchanged because the missing atoms create spaces within the lattice that are filled by neighboring atoms. Therefore, the mass per unit volume, and thus the density, remains constant.
Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
The point defect that alters the density of a solid is known as a "vacancy." In a crystal lattice, a vacancy occurs when an atom or ion is missing from its regular position. This creates a local disruption in the crystal structure, leading to a decrease in density because there is less mass occupying the volume. Vacancies can occur naturally due to thermal energy or can be intentionally introduced through processes such as irradiation or doping during material synthesis.
read lessAnswered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
In general, point defects such as vacancies, interstitials, and substitutional impurities can affect the density of a solid material. However, among these defects, the presence of interstitials typically increases the density of a solid.
Interstitial defects occur when atoms occupy spaces between the regular lattice sites of the crystal structure. Since these atoms are located in the interstitial spaces, they add to the overall mass and increase the density of the material. This increase in density is because the additional atoms effectively reduce the amount of empty space within the crystal lattice.
Therefore, the presence of interstitial point defects tends to increase the density of a solid material.
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Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
Metallic and ionic substances differ significantly in their ability to conduct electricity due to the nature of their bonding and the movement of their constituent particles:
Metallic Substances:
Ionic Substances:
In summary, metallic substances conduct electricity due to the free movement of delocalized electrons, whereas ionic substances conduct electricity when dissolved in water or melted, allowing the ions to become mobile.
Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
The point defect that decreases the density of a solid is called a "vacancy defect." In a vacancy defect, atoms are missing from their lattice sites in the crystal structure, leaving empty spaces or vacancies. This reduction in the number of atoms per unit volume leads to a decrease in the overall density of the solid.
read lessAnswered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
In a face-centered cubic (FCC) crystal lattice, each corner of the unit cell is shared among eight neighboring unit cells, and each face-centered atom is shared among two neighboring unit cells. Therefore, each unit cell contains:
So, the total number of atoms in a unit cell of an FCC crystal lattice is:
8×18+6×12=1+3=48×81+6×21=1+3=4
Therefore, there are 4 atoms in a unit cell of a face-centered cubic crystal.
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Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
One feature that can distinguish a metallic solid from an ionic solid is their electrical conductivity behavior.
So, a feature to distinguish between the two would be to test the electrical conductivity of the solid. If the solid conducts electricity in the solid state, it is likely to be metallic. If it only conducts electricity when molten or dissolved, it is likely to be ionic.
Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
A "vacancy" is a point defect in crystals that does not change the density of the solid. This is because a vacancy is simply an empty space where an atom should be located within the crystal lattice. When an atom is missing from the lattice structure, it creates a vacancy defect. However, the overall volume of the crystal remains the same because the missing atom's volume is essentially replaced by the vacant space. Therefore, vacancies do not alter the density of the solid.
read lessAnswered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
The point defect in crystals of a solid that typically decreases the density of the solid is known as a "vacancy defect."
In a vacancy defect, some of the lattice sites in the crystal are unoccupied by atoms. This creates empty spaces within the crystal structure, which reduces the effective mass and, consequently, the density of the material.
So, vacancies effectively decrease the density of the solid because they reduce the overall mass of the crystal without significantly altering its volume.
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Answered on 07 Apr Learn Unit I: Solid State
Nazia Khanum
In a polar molecular solid, the molecules are held together primarily by dipole-dipole interactions.
Dipole-dipole interactions occur between polar molecules, where one end of the molecule has a partial positive charge and the other end has a partial negative charge. These partial charges create an electrostatic attraction between neighboring molecules, leading to the formation of a solid structure.
In addition to dipole-dipole interactions, polar molecular solids may also experience other intermolecular forces such as hydrogen bonding, van der Waals forces, and London dispersion forces, depending on the specific molecules involved and their structures. However, dipole-dipole interactions are typically the dominant force in polar molecular solids.
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