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Questions and Answers
What is a characteristic feature of a vacancy defect?
What is a characteristic feature of a vacancy defect?
How does an interstitial defect affect the density of a substance?
How does an interstitial defect affect the density of a substance?
In a Frenkel defect, what happens to the smaller ion in ionic solids?
In a Frenkel defect, what happens to the smaller ion in ionic solids?
Which of the following statements is true regarding Schottky defects?
Which of the following statements is true regarding Schottky defects?
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Which statement describes line defects?
Which statement describes line defects?
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What is typically a cause for the formation of edge defects in crystals?
What is typically a cause for the formation of edge defects in crystals?
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What is the expected vapor pressure of a substance at 363 K?
What is the expected vapor pressure of a substance at 363 K?
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What is the estimated energy required for sublimation of ice based on its vapor pressures at 268 K and 273 K?
What is the estimated energy required for sublimation of ice based on its vapor pressures at 268 K and 273 K?
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What results from vacancy condensation in crystalline structures?
What results from vacancy condensation in crystalline structures?
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When the vapor pressure of ethanol at 34.9 ˚C is 115 torr, what is its heat of vaporization?
When the vapor pressure of ethanol at 34.9 ˚C is 115 torr, what is its heat of vaporization?
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Which defect type incorporates both vacancy and interstitial effects?
Which defect type incorporates both vacancy and interstitial effects?
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At what temperature does the vapor pressure of ethanol reach 760 torr based on the heat of vaporization provided?
At what temperature does the vapor pressure of ethanol reach 760 torr based on the heat of vaporization provided?
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What is the octet rule in atomic structure?
What is the octet rule in atomic structure?
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In solids, how do atoms move when they are closely arranged together?
In solids, how do atoms move when they are closely arranged together?
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What is the primary effect of doping in semiconductors?
What is the primary effect of doping in semiconductors?
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Which of the following correctly describes the behavior of valence electrons?
Which of the following correctly describes the behavior of valence electrons?
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What is the phase diagram commonly used for?
What is the phase diagram commonly used for?
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Which type of semiconductor uses higher valence elements as donor atoms?
Which type of semiconductor uses higher valence elements as donor atoms?
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What does the presence of donor atoms do to the Fermi energy level in semiconductors?
What does the presence of donor atoms do to the Fermi energy level in semiconductors?
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Using the formula $R = \frac{pL}{A}$, which parameter does NOT affect the resistance of a material?
Using the formula $R = \frac{pL}{A}$, which parameter does NOT affect the resistance of a material?
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What is the resistivity of tungsten according to the provided resistivity values?
What is the resistivity of tungsten according to the provided resistivity values?
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In the resistance calculation example provided, what was the calculated resistance of the copper wire?
In the resistance calculation example provided, what was the calculated resistance of the copper wire?
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What electrical property is uniquely characteristic of semiconductors compared to conductors and insulators?
What electrical property is uniquely characteristic of semiconductors compared to conductors and insulators?
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What is the diameter of a tungsten filament with a length of 4.00 cm and a resistance of 0.350 Ω?
What is the diameter of a tungsten filament with a length of 4.00 cm and a resistance of 0.350 Ω?
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Study Notes
Course Information
- Course title: CHEM 004 – Material Science and Engineering
- Department: Department of Environmental and Sanitary Engineering
- Institution: Technological Institute of the Philippines – Q.C
- Presenter: Engr. Andrey Joshua Antiporta
Atomic Structure and Bonding
- Valence electrons are located at the outermost shell of an atom
- Electrons tend to form pairs for stability
- Unpaired electrons tend to gain other electrons from another atom
- Atoms are composed of a nucleus containing protons and neutrons, with electrons orbiting the nucleus
- Protons are positively charged
- Neutrons are neutral
- Electrons are negatively charged
- 1 Å = 100 pm
Ionic Bonding
- Occurs between positive and negative ions (cations and anions)
- Electron transfer is necessary
- Large difference in electronegativity is required
- Example: NaCl (sodium chloride)
- Nondirectional bonding, meaning the bond does not have a specific direction
Covalent Bonding
- Covalent bonds involve sharing of electrons
- Atoms share electrons to gain stability
- Electronegativities of atoms are similar or comparable
- Example: H2, CH4
Metallic Bonding
- Metals tend to form bonds by collective sharing of delocalized electrons
- Delocalized electrons give metals their conductive properties
Inter-molecular or Secondary Bonds
- Dipole-Dipole Interactions occur when two molecules have polar charges (dipoles).
- These charges are weak.
- Hydrogen bonding is a type of secondary bonding (an example of dipole-dipole)
Bonding Forces and Energy
- Primary bonding: Ionic, Covalent, Metallic
- Secondary bonding: Dipole-dipole, H-bonds
- Bonding energies and melting temperatures vary for different substances
- Ionic bonds tend to have large bonding energies
- Covalent bonds vary but are moderate
- Metallic bonds are variable and moderate
- Secondary bonds have the lowest bond energy
Mechanical Properties of Solids
- Elasticity is the tendency of a material to return to its original shape after stress is applied.
- Stress is force applied to a material.
- Strain is deformation caused by stress.
Crystalline Structures
- Solids are characterized by structural rigidity and resistance to applied forces.
- Crystalline solids have a highly ordered, repeating arrangement of atoms or molecules in a periodic lattice.
- Polycrystalline structures are comprised of many small crystals in a random arrangement
- Amorphous solids have no long-range order
Imperfections in Solids
- Imperfections, or defects, can occur in crystalline structures, leading to unique properties
- Impurities are often present in a metal
- Dislocation defects result from the presence of atoms in planes and/or directions of slip
- Point defects: vacancy, interstitial defects
- Frenkel defect: smaller ion (cation) moves out of its place and occupies an intermolecular space; a vacancy defect is created on its original position and the interstitial defect is experienced in its new position
- Schottky defect: equal number of anions and cations are missing from the compound
Semiconductor Doping
- Doping is introducing impurities into an intrinsic semiconductor.
- Extrinsic semiconductors are doped with impurities.
- P-type dopants are used when extra electrons are required
- N-type impurities are used when extra electron holes are required
Unit Cell
- Unit cell is the smallest repeating unit of a crystalline structure.
- Types of unit cell: Simple cubic, Body-centered cubic (BCC), Face-centered cubic (FCC)
- Density is related to the unit cell
Diffusion
- Diffusion is the process by which atoms or molecules move from a region of higher concentration to a region of lower concentration.
- Mechanisms: Substitutional diffusion, Vacancy diffusion, Interstitial diffusion
- Factors that affect the rate of diffusion: temperature, type of material, type of diffusing atoms
Phase Diagrams
- Phase diagrams show the phases of a substance at various temperatures and pressures
- Triple point: the temperature and pressure where all three phases (solid, liquid, gas) coexist in equilibrium
- Critical point: the point beyond where a liquid cannot exist
- Fusion/Melting curve: the curve representing solid to liquid
- Vaporization curve: the curve representing liquid to gas
- Sublimation curve: the curve representing solid to gas
Electrical Properties
- A conductor allows the easy flow of electrons
- An insulator does not allow any flow of electrons
- A semiconductor is intermediate, and its behavior depends on temperature
Thermal Properties
- Thermal expansion is the tendency of a substance to increase in size due to temperature increases.
- Linear and volumetric coefficients determine the amount of expansion.
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