Material Science: Atomic Structure, Bonding, and Crystal Defects

Vocabulary flashcards covering key terms and concepts from Chapter 2 on atomic structure, bonding types, crystal lattices, defects, and mechanical behaviors.

Atom

The basic structural unit of matter.

Atomic Number

The number of protons located in the nucleus of an atom.

Valence Electrons

Electrons located in the outermost electron shell that strongly influence bonding and chemical reactivity.

Electron Shell Capacity Formula

The relationship $2n^2$, which determines the maximum number of electrons in the $n$th electron shell (e.g., $8$ electrons in the second shell).

Primary Bonds

Strong interatomic bonds comprising ionic, covalent, and metallic bonds.

Ionic Bond

A primary bond formed by the transfer of one or more valence electrons from one atom to another.

Covalent Bond

A primary bond in which atoms share valence electrons.

Metallic Bond

A primary bond in which outer-shell electrons are shared collectively and can move freely throughout the material, providing high electrical conductivity.

Secondary Bond

Relatively weak intermolecular attraction such as dipole forces, London forces, or hydrogen bonding.

London Bond

A secondary bond resulting from temporary charge imbalances produced by electron movement.

Crystalline Structure

An atomic arrangement characterized by regular, repeating long-range order in three dimensions.

Unit Cell

The basic geometric grouping of atoms that repeats throughout a crystal lattice.

Body-Centered Cubic (BCC)

A unit cell structure containing atoms at the eight corners and one atom at the center of the cell.

Face-Centered Cubic (FCC)

A crystal structure found in metals like copper, generally considered the most ductile metallic structure at room temperature.

Hexagonal Close-Packed (HCP)

A metallic crystal structure with fewer available slip directions that is often less ductile at room temperature than FCC.

Allotropy

The ability of a material to exist in different crystal structures at different temperatures.

Vacancy

A point defect occurring when an atom is missing from its normal position in the crystal lattice.

Interstitialcy

A point defect where an extra atom occupies a position between normal lattice sites.

Frenkel Defect

A crystal defect occurring when an ion leaves its normal lattice position and moves into an interstitial position.

Schottky Defect

A defect in which a pair of oppositely charged ions is missing from the lattice while maintaining overall charge balance.

Dislocation

A line defect in a crystal lattice that allows atomic movement to occur in smaller steps at lower stresses during plastic deformation.

Edge Dislocation

A line defect produced by the edge of an extra plane of atoms within a crystal lattice.

Screw Dislocation

A line defect characterized by a spiral distortion around a line through the lattice.

Plastic Deformation

Deformation causing atoms to permanently move to new positions so that deformation does not disappear when the load is removed.

Slip

A plastic deformation mechanism involving the relative movement of atoms on opposite sides of a crystallographic plane.

Twinning

A plastic deformation mechanism in which atoms shift to form a mirror-image arrangement across a plane, active when slip is difficult or deformation rate is high.

Grain

An individual crystal within a polycrystalline material.

Grain Boundary

The interface between adjacent crystals having different lattice orientations that interferes with dislocation movement to strengthen the metal.

Amorphous Structure

An atomic arrangement lacking regular, repeating long-range order, formed when molten material is cooled extremely rapidly.

Glass-Transition Temperature

The temperature associated with the transition of an amorphous material from a rigid glassy state to a progressively softer condition.

Ceramics

Materials held together by ionic and/or covalent bonding, typically characterized as hard, stiff, and generally brittle.

Polymers

Materials featuring covalent bonding along the molecular chains and secondary bonding acting between neighboring chains.