Glossary
Alloys
Mixtures of two or more elements, where at least one is a metal, created to enhance specific metallic properties.
Example:
Bronze, an alloy of copper and tin, is much harder and more durable than pure copper, making it suitable for sculptures.
Amorphous Solids
Solids that lack a long-range, repeating structural order, often forming when a liquid cools too rapidly for crystals to form.
Example:
The irregular fracture pattern of glass indicates it is an amorphous solid, unlike the sharp, defined faces of a quartz crystal.
Brittle
A property of materials that causes them to break or shatter easily when subjected to stress, rather than deforming.
Example:
Ceramic plates are brittle; if dropped, they tend to shatter into many pieces rather than bending.
Coulomb's Law
A law stating that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
Example:
According to Coulomb's Law, a smaller ionic radius or higher ionic charge leads to stronger electrostatic attractions in an ionic solid, resulting in a higher melting point.
Covalent Network Solids
Solids in which atoms are held together by a vast, continuous network of strong covalent bonds throughout the entire structure.
Example:
The extreme hardness of a diamond is due to its nature as a covalent network solid, where each carbon atom is covalently bonded to four others.
Crystal Lattice
The geometrical arrangement of points in space that describes the repeating pattern of atoms, ions, or molecules in a crystalline solid.
Example:
The precise arrangement of sodium and chloride ions forms the cubic crystal lattice of table salt.
Crystalline Solids
Solids with particles arranged in a highly ordered, repeating three-dimensional pattern, resulting in a definite melting point.
Example:
Most gemstones, like emeralds, are crystalline solids due to their precise, repeating atomic arrangements.
Delocalized Electrons
Electrons that are not confined to a single atom or bond but are free to move throughout a larger region of a molecule or solid.
Example:
The excellent electrical conductivity of metals is attributed to their delocalized electrons, which can flow freely under an applied voltage.
Diamond
An allotrope of carbon where each carbon atom is sp3 hybridized and covalently bonded to four other carbon atoms in a tetrahedral arrangement, making it extremely hard and an insulator.
Example:
Industrial cutting tools often use diamond because its rigid covalent network structure makes it the hardest known natural material.
Ductile
A property of materials, typically metals, that allows them to be drawn into thin wires without breaking.
Example:
Copper is highly ductile, which is why it is extensively used for electrical wiring.
Graphite
An allotrope of carbon that forms layers of sp2 hybridized carbon atoms arranged in hexagonal rings, known for its conductivity and softness.
Example:
The lead in pencils is actually graphite, which is soft enough for its layers to slide past each other, leaving a mark on paper.
Intermolecular Forces (IMFs)
Attractive forces that exist between molecules, influencing the physical properties of molecular substances like melting and boiling points.
Example:
The relatively low boiling point of water compared to ionic compounds is due to the presence of hydrogen bonding, a type of strong intermolecular force.
Interstitial Alloy
An alloy where smaller atoms fit into the spaces (interstices) between larger atoms in the crystal lattice.
Example:
Steel is an interstitial alloy where small carbon atoms occupy the gaps between larger iron atoms, increasing its strength.
Intramolecular Forces
The strong attractive forces that hold atoms together within a molecule, such as covalent or ionic bonds.
Example:
The strong covalent bonds holding hydrogen and oxygen atoms together within a single water molecule are examples of intramolecular forces.
Ionic Solids
Solids composed of cations and anions held together by strong electrostatic forces, forming a crystal lattice.
Example:
Table salt, NaCl, is an example of an ionic solid where Na+ and Cl- ions are strongly attracted.
Malleable
A property of materials, typically metals, that allows them to be hammered or pressed into thin sheets without breaking.
Example:
Aluminum foil demonstrates the malleable nature of aluminum, allowing it to be flattened into very thin sheets.
Metallic Solids
Solids composed of metal atoms held together by metallic bonds, characterized by a 'sea' of delocalized valence electrons.
Example:
A copper wire, Cu(s), is a metallic solid whose free-moving electrons allow it to conduct electricity efficiently.
Molecular Solids
Solids composed of discrete molecules held together by relatively weak intermolecular forces (IMFs).
Example:
Dry ice, CO2(s), is a molecular solid that sublimes easily because the weak London Dispersion Forces between CO2 molecules are readily overcome.
Substitutional Alloy
An alloy where atoms of one element replace atoms of another element in the crystal lattice, typically when the atomic radii are similar.
Example:
Brass, an alloy of copper and zinc, is a substitutional alloy because zinc atoms replace some copper atoms in the lattice.
Unit Cell
The smallest repeating unit of a crystal lattice that, when repeated in three dimensions, generates the entire crystal structure.
Example:
In a simple cubic structure, the unit cell is a cube with an atom at each corner, serving as the fundamental building block.