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Questions and Answers
What is the total number of atoms in one face-centred cubic unit cell?
What is the total number of atoms in one face-centred cubic unit cell?
Which type of unit cell has its atoms arranged such that $a
eq b
eq c$ and $oldsymbol{eta}
eq 120°$?
Which type of unit cell has its atoms arranged such that $a eq b eq c$ and $oldsymbol{eta} eq 120°$?
What is the packing efficiency of both hexagonal close-packed and cubic close-packed structures?
What is the packing efficiency of both hexagonal close-packed and cubic close-packed structures?
What kind of voids are formed in hexagonal close-packed structures?
What kind of voids are formed in hexagonal close-packed structures?
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Which of the following is NOT a type of primitive unit cell?
Which of the following is NOT a type of primitive unit cell?
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In which unit cell type are the particles arranged with $a = b
eq c$ and $oldsymbol{eta}
eq 90°$?
In which unit cell type are the particles arranged with $a = b eq c$ and $oldsymbol{eta} eq 90°$?
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What is the coordination number definition?
What is the coordination number definition?
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Which primitive unit cell is characterized by $a = b = c$ and $oldsymbol{eta}
eq 90°$?
Which primitive unit cell is characterized by $a = b = c$ and $oldsymbol{eta} eq 90°$?
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Which characteristic is NOT associated with solids?
Which characteristic is NOT associated with solids?
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What distinguishes crystalline solids from amorphous solids concerning melting behavior?
What distinguishes crystalline solids from amorphous solids concerning melting behavior?
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Which type of solid includes sodium chloride (NaCl) as a representative example?
Which type of solid includes sodium chloride (NaCl) as a representative example?
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What property is shared by amorphous solids?
What property is shared by amorphous solids?
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Which type of molecular solid is characterized by dipole-dipole interactions?
Which type of molecular solid is characterized by dipole-dipole interactions?
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Which type of solid is diamond classified as?
Which type of solid is diamond classified as?
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Which statement accurately differentiates between anisotropic and isotropic materials?
Which statement accurately differentiates between anisotropic and isotropic materials?
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Which of the following is NOT a characteristic of crystalline solids?
Which of the following is NOT a characteristic of crystalline solids?
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What is the packing efficiency of a body-centered cubic (bcc) lattice?
What is the packing efficiency of a body-centered cubic (bcc) lattice?
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How many octahedral voids are found in a close-packed structure?
How many octahedral voids are found in a close-packed structure?
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Which type of defect involves a foreign atom replacing a host atom in the lattice?
Which type of defect involves a foreign atom replacing a host atom in the lattice?
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What results from a vacancy defect in a substance?
What results from a vacancy defect in a substance?
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Which of the following is true regarding tetrahedral voids?
Which of the following is true regarding tetrahedral voids?
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What is a characteristic of Schottky defects?
What is a characteristic of Schottky defects?
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Which type of lattice defect is typically associated with a large difference in the size of ions?
Which type of lattice defect is typically associated with a large difference in the size of ions?
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What contributes to a metal excess defect?
What contributes to a metal excess defect?
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Study Notes
General Characteristics of Solids
- Solids have a definite mass, volume, and shape.
- Molecules in solids are tightly packed with short intermolecular distances and strong intermolecular forces.
- Constituent particles of solids are arranged in a fixed lattice position.
- Solids are incompressible and rigid.
Classification of Solids
- Solids are classified as crystalline or amorphous.
- Crystalline solids have a regular, repeating arrangement of particles, resulting in sharp melting points and anisotropic properties.
- Amorphous solids lack a long-range order in their structure, leading to gradual softening over a range of temperatures and isotropic properties.
Types of Crystalline Solids
-
Molecular solids: Exist as individual molecules held together by weak intermolecular forces like Van der Waals forces or hydrogen bonding.
- Non-polar molecular solids: Molecules consist of atoms or non-polar covalent bonds, like H2, Cl2, and I2.
- Polar molecular solids: Molecules are held by strong dipole-dipole interactions, like solid SO2 and solid NH3.
- Hydrogen-bonded molecular solids: Contain polar covalent bonds between H and F, O, or N, like ice (H2O).
-
Ionic solids: Composed of ions held together by electrostatic forces, example: NaCl and KNO3.
-
Metallic solids: Atoms are surrounded by a "sea" of delocalized electrons, example: Fe and Cu.
-
Covalent or Network solids: Atoms held together by strong covalent bonds forming a vast network structure, example: diamond and silicon carbide.
Crystal Lattice and Unit Cells
- Crystal lattice: A three-dimensional arrangement of points representing the positions of constituent particles in a crystal. There are 14 Bravais lattices.
-
Unit cell: Smallest repeating unit of a crystal lattice. There are two types:
- Primitive unit cells: Seven types of primitive unit cells based on the shape and angles of the unit cell.
- Centred unit cells: Have additional atoms located at the center of the unit cell (body-centered, face-centered, or end-centered).
Number of Atoms in a Unit Cell
- Primitive cubic unit cell: Contains 1 atom.
- Body-centered cubic unit cell: Contains 2 atoms.
- Face-centered cubic unit cell: Contains 4 atoms.
Close-Packed Structures
- Coordination number: The number of nearest neighbors surrounding a particle.
- Packing efficiency: The percentage of space filled by particles in a crystal structure.
Close-Packing in Three Dimensions
- Two main types of close-packed structures:
- Hexagonal close-packed (hcp).
- Cubic close-packed (ccp) or face-centered cubic (fcc) lattice.
- Both hcp and ccp have a packing efficiency of 74%.
-
Voids: Empty spaces in close-packed structures:
- Octahedral voids: Occur between six spheres.
- Tetrahedral voids: Occur between four spheres.
- The number of octahedral voids equals the number of close-packed particles, while the number of tetrahedral voids is twice the number of close-packed particles.
Packing Efficiency in Non-Close-Packed Structures
- Body-centered cubic (bcc) structure has a packing efficiency of 68%.
- Simple cubic lattice has a packing efficiency of 52.4%.
Ionic Crystal Structures
- Larger ions (anions) typically form the close-packed structure, with smaller ions (cations) occupying the voids.
- The fraction of occupied voids depends on the chemical formula of the compound.
Calculations Involving Unit Cells
-
Density of a unit cell:
$Density\ of\ a\ unit\ cell = \dfrac{Mass\ of\ the\ unit\ cell}{Volume\ of\ the\ unit\ cell} = \dfrac{zM}{a^3N_A}$
Where:
- $d$ = Density
- $z$ = Number of atoms in one unit cell
- $M$ = Molar mass
- $a$ = Edge length of the unit cell
- $N_A$ = Avogadro's number
Imperfections in Solids
- Defects: Deviations from the perfect arrangement of particles in a crystal.
- Line defects: Irregularities in the arrangement of particles along entire rows of a lattice point.
- Point defects: Irregularities in the arrangement of particles around a specific point or atom.
Types of Point Defects
-
Stoichiometric defects (Intrinsic or thermodynamic defects):
- Vacancy defect: Missing particle at a lattice site, created by heating.
- Interstitial defect: An extra particle occupying a position between lattice sites.
- Frenkel defect: A cation leaves its lattice site and occupies an interstitial position, occurring in ionic solids with large size differences between ions.
- Schottky defect: Pair of vacancies (cation and anion) in ionic solids, reducing density.
-
Impurity defects: Foreign atoms replacing host atoms at lattice sites.
-
Non-stoichiometric defects: Occur when the ratio of cations to anions deviates from the ideal stoichiometric ratio in the compound:
- Metal excess defect: Occurs due to anionic vacancies or the presence of extra cations.
- Metal deficiency defect: Occurs in compounds with transition metals showing variable valency.
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Description
This quiz covers the essential characteristics and classification of solids, focusing on key aspects such as the arrangement of particles, types of solids, and their properties. Understand the differences between crystalline and amorphous solids while exploring examples of each type. This knowledge is crucial for studying the states of matter in physics and chemistry.
