enel290 test 1

What does Avogadro’s number represent?

The number of particles (atoms, molecules, or ions) in 1 mole of a substance (or the exact number of atoms in 12 grams of carbon-12).

What is a key characteristic of metallic bonds?

Electrons are delocalized and shared among many atoms.

What differentiates isotopes of the same element?

They have different numbers of neutrons (giving them different mass numbers, while keeping the same number of protons).

How are resistivity and conductivity related?

Inversely related. Resistivity measures opposition to current, while conductivity measures the ease of current flow.

What does the quantum mechanical model of the atom suggest about electron positions?

Electrons do not follow precise paths; they are found in orbitals, which are 3D regions representing the probability of finding an electron.

What is the atomic packing factor (APF) in crystallography?

The fraction (or percentage) of volume in a unit cell that is occupied by atoms.

Mnemonic for which common elemental metals have a Hexagonal Close Packing (HCP) crystal structure?

Happy Cats Purr: My Zoo Takes Care of Big Cats — Mg, Zn, Ti, Co, Be, Cd.

Mnemonic for which common elemental metals have a Face-Centered Cubic (FCC) crystal structure?

Famous Chemistry Class: All Clever Geeks Study Nice Physics Laws — Al, Cu, Au, Ag, Ni, Pt, Pb.

What stacking sequence and Atomic Packing Factor (APF) characterize a Hexagonal Close-Packed (HCP) crystal structure?

An ABAB... (or ABA) stacking sequence of close-packed planes, with an APF of 74% (0.74).

What is a mnemonic to remember Body-Centered Cubic (BCC) metals?

Big Cold Cave: Feeling Cold? Warm Medium Tea, Very Nice. Fe, Cr, W, Mo, Ta, V, Na.

What type of crystal defect is characterized by an extra half-plane of atoms terminating within a crystal?

An edge dislocation (a 1D or line defect)

What causes a vacancy defect in a crystal structure?

An atom is missing from its normal lattice site (leaving an empty space).

How does thermal expansion affect crystal structures?

Increased thermal energy causes greater atomic vibrations and interatomic spacing, causing the crystal lattice to expand with rising temperature.

What is the primary role of conductors in electrical applications?

To move electrical signals or current efficiently from one point to another.

What defines ionic bonding?

The transfer of valence electrons from one atom to another, forming oppositely charged ions.

What is the atomic packing factor (APF) of a BCC crystal structure?

68% (0.68)

What is the coordination number in a crystal structure?

The number of nearest neighboring atoms directly touching an individual atom

What type of defect occurs where two crystal grains of different orientations meet?

A grain boundary defect (a 2D planar/interfacial defect).

What are the official geometric categories of crystal defects?

Point (0D), Line (1D), Planar/Interfacial (2D), and Volume/Bulk (3D) defects. ("Thermal defect" is not a standard structural category).

What are the coordination numbers for BCC, FCC, and HCP crystal structures?

BCC = 8; FCC = 12; HCP = 12.

What is the difference between a Frenkel defect and a Schottky defect?

Frenkel Defect: An ion jumps from its lattice site into a nearby interstitial space (creates a vacancy–interstitial pair).

Schottky Defect: A cation and an anion are both missing from the lattice, maintaining overall charge neutrality.

How is the Burgers vector oriented relative to the dislocation line in edge vs. screw dislocations?

Edge dislocation: Burgers vector is perpendicular to the dislocation line.

Screw dislocation: Burgers vector is parallel to the dislocation line.

What is the difference between a substitutional impurity and an interstitial impurity?

Substitutional: An impurity atom replaces a main host atom at its regular lattice site.

Interstitial: A smaller impurity atom squeezes into the empty voids between host atoms.

What defines covalent bonding compared to ionic and metallic bonding?

Electrons are shared directly between specific adjacent non-metal atoms in directional bonds (unlike electron transfer in ionic bonds or delocalized pools in metallic bonds).

How do grain boundaries affect the mechanical strength of a metal (Hall-Petch effect)?

Grain boundaries block dislocation movement. Smaller grain size means more grain boundaries, making the metal stronger and harder.

What is the Atomic Packing Factor (APF) of Simple Cubic (SC) and Diamond Cubic structures?

Simple Cubic: 52% (0.52)

Diamond Cubic: 34% (0.34)

What does the atomic number specify, and why is it important in semiconductor physics?

Specifies the number of protons in an atom's nucleus; it is used to calculate the number of free charge carriers and donor atoms in semiconductors.

What is atomic weight, and what parameter can be derived from it?

The normalized weight of an atom; it is used to derive isotope abundance.

Why is crystal structure an important periodic property in materials science?

It is critical for understanding interfaces, molecules, and compound semiconductors.

What physical property is directly governed by an atom's valence-shell configuration?

Electrical conductivity.

What is an allotrope?

Different structural or crystalline forms of the same pure chemical element in the same physical state, affecting it’s physical and electronic properties. (also called polymorphism)

How are resistance, length, and cross sectional area linked?

Resistance increases with length and decreases with cross-sectional area A

What valence electron pattern do conventional tetrahedrally bonded semiconductors follow?

They have an average of 4 valence electrons per atom (or 8 total valence electrons per binary pair)

Ranges of conductivity for each type (dielectric, semiconductor, conductor) (in S/METRE)

dielectric: <10×10^-10
condutor: >10×10^2

semiconductors basically anywhere between