Solids and Modern Materials Vocabulary

Flashcards containing key vocabulary terms and definitions from Chapter 13: Solids and Modern Materials.

Graphene

The thinnest and strongest known material, consisting of a single layer of carbon atoms one atom thick that conducts heat and electricity and is impermeable to all substances.

Crystalline Solid

A solid composed of atoms, ions, or molecules arranged in structures with long-range order.

Amorphous Solid

A solid composed of atoms or molecules with no long-range order.

X-Ray Crystallography

A powerful technique using X-ray diffraction to determine the arrangement of atoms and measure interatomic distances within a crystal.

Bragg's Law

An equation, $n\times\frac{\text{wavelength}}{2d} = \text{sin}(\theta)$ or $n\times\frac{\text{wavelength}}{2\text{sin}(\theta)} = d$, mathematically written as $n\times\frac{\text{wavelength}}{2d} = \text{sin}(\theta)$, that relates diffraction order $n$, wavelength $\frac{n\times\text{wavelength}}{2\text{sin}(\theta)}$, atomic plane spacing $d$, and angle $\theta$.

Crystal Lattice

The regular, three-dimensional arrangement of atoms, ions, or molecules within a crystalline solid.

Unit Cell

The smallest repeating unit of a crystal lattice that displays the symmetry and structural pattern of the entire crystal.

Simple Cubic Unit Cell

A cubic unit cell containing $\frac{1}{8}$ of an atom at each of its $8$ corners for a total of $1$ atom per cell, with an edge length of $a = 2r$, a coordination number of $6$, and a packing efficiency of $52\%$.

Body-Centered Cubic (bcc) Unit Cell

A cubic unit cell containing $\frac{1}{8}$ of an atom at each of its $8$ corners plus $1$ central atom for a total of $2$ atoms per cell, with an edge length of $a = \frac{4r}{\sqrt{3}}$, a coordination number of $8$, and a packing efficiency of $68\%$.

Face-Centered Cubic (fcc) Unit Cell

A cubic unit cell containing $\frac{1}{8}$ of an atom at each of its $8$ corners plus $\frac{1}{2}$ of an atom on each of its $6$ faces for a total of $4$ atoms per cell, with an edge length of $a = 2\sqrt{2}r$, a coordination number of $12$, and a packing efficiency of $74\%$.

Coordination Number

The number of atoms or ions immediately adjacent to any given atom or ion in a crystal structure.

Packing Efficiency

The fraction of total unit cell volume occupied by atoms, calculated as the volume occupied by atoms divided by the total volume of the unit cell times $100\%$.

Hexagonal Closest-Packed (hcp) Structure

A close-packed crystal structure formed by an $ABAB...$ layer stacking pattern with a coordination number of $12$ and a packing efficiency of $74\%$.

Cubic Closest-Packed (ccp) Structure

A close-packed crystal structure formed by an $ABCABC...$ layer stacking pattern, structurally equivalent to a face-centered cubic lattice.

Molecular Solids

Crystalline solids whose composite units are molecules held together by intermolecular forces (dispersion, dipole–dipole, or hydrogen bonding), resulting in relatively low melting points.

Polymorphs

Different crystalline structures in which a single compound can solidify, often having distinct melting points, solubilities, and physiological activities.

Ionic Solids

Crystalline solids composed of cations and anions held together by ionic bonds, featuring high melting points and conducting electricity when molten or dissolved.

Nonbonding Atomic Solids

Atomic solids held together by weak dispersion forces with very low melting points, exemplified by solid noble gases.

Metallic Atomic Solids

Atomic solids consisting of metal cations fixed in a sea of mobile electrons held together by metallic bonds, displaying variable melting points.

Network Covalent Solids

Atomic solids whose atoms are held together in a continuous network of covalent bonds, characterized by very high melting points.

Cesium Chloride (CsCl) Structure

An ionic crystal structure with a $1:1$ stoichiometry where $Cl^-$ ions form a simple cubic frame and $Cs^+$ occupies the central site, yielding a coordination number of $8$.

Sodium Chloride (NaCl) Structure

An ionic rock salt structure based on a face-centered cubic lattice where each $Na^+$ ion is surrounded by $6$ $Cl^-$ ions and vice versa.

Zinc Blende (ZnS) Structure

An ionic crystal structure based on a face-centered cubic array of $S^{2-}$ anions with $Zn^{2+}$ cations filling $4$ of the $8$ tetrahedral holes, giving a coordination number of $4$.

Fluorite Structure

An ionic structure adopted by compounds with a $1:2$ cation-to-anion ratio (such as $CaF_2$), where cations form a face-centered cubic array and anions occupy all $8$ tetrahedral holes.

Antifluorite Structure

An ionic crystal structure adopted by compounds with a $2:1$ cation-to-anion ratio, where anions form an fcc array and cations occupy tetrahedral holes.

Graphite

A crystalline allotrope of carbon consisting of fused six-membered rings of $sp^2$-hybridized carbon atoms in flat sheets held together by weak dispersion forces.

Diamond

A network covalent allotrope of carbon in which each carbon atom is $sp^3$-hybridized and bonded tetrahedrally to $4$ surrounding carbon atoms.

Fullerenes

Spherical clusters of carbon atoms (buckyballs), such as $C_{60}$, composed of interconnected hexagonal and pentagonal carbon rings.

Carbon Nanotubes

Cylindrical carbon structures composed of rolled sheets of interconnected six-membered carbon rings.

Silicates

Extended network covalent materials forming around $90\%$ of Earth's crust, constructed from tetrahedral $SiO_4$ units.

Ceramics

Inorganic, nonmetallic solids prepared from powders mixed with water, shaped, and hardened by high-temperature heating.

Refractory Materials

High-temperature-resistant materials, such as oxide ceramics ($Al_2O_3$ and $MgO$), capable of withstanding industrial furnace temperatures without melting.

Portland Cement

A hydraulic cement mixture consisting mostly of limestone ($CaCO_3$) and silica ($SiO_2$) with alumina ($Al_2O_3$), iron(III) oxide ($Fe_2O_3$), and gypsum ($CaSO_4 \cdot 2H_2O$).

Glass

An amorphous solid produced by quickly cooling molten silica ($SiO_2$) to prevent crystallization.

Band Theory

A model based on molecular orbital theory where atomic orbitals in a crystal combine into continuous, delocalized energy bands extending over the entire solid.

Valence Band

In band theory, the band of delocalized molecular orbitals that holds valence electrons.

Conduction Band

In band theory, the band of unoccupied orbitals lying higher in energy above the valence band where electron movement allows electrical conduction.

Band Gap

The energy difference between the top of the valence band and the bottom of the conduction band in a solid.

Semiconductor

A material with an intermediate energy band gap between its valence and conduction bands, resulting in partial electrical conductivity.

Doping

The addition of trace amounts of an impurity element to a semiconductor crystal to modify its electrical properties.

n-Type Semiconductor

A semiconductor prepared by doping with a valence-electron-rich element (such as doping $Si$ with $P$) that introduces extra negative charge carriers.

p-Type Semiconductor

A semiconductor prepared by doping with a valence-electron-deficient element (such as doping $Si$ with $Al$) that creates positive electron vacancies ("holes").

Diode

A semiconductor device formed by adjoining p-type and n-type semiconductors ($p\text{--}n$ junction) that allows current to flow in only one direction.