Unit 12: Solids

Molecular Solid - held together by intermolecular forces

Metallic solid - positive cores of atoms held together by a surrounding

Ionic solid - cations and anions held together by electrical attraction (ionic bond)

Covalent solid - atom held together in large networks or chains by covalent bonds

White phosphorus - Molecular solid based on P4 tetrahedra, waxy, soft solid; burns in air

Red phosphorus - stable in air, polymer of covalently linked P4 tetrahedra

Melting point and structure of ionic and covalent solids - melting points are relatively high, because melting involves breaking chemical bonds

Melting point and structure of ionic solids - melting points increase with strength of the ionic bond

Melting point and structure of metals - often have high melting points

Melting point and structure of molecular solids - tend to have lower melting points

Metallic Bonds - Dense packing of metal atoms results in overlap of large number of valence orbitals, large number of interactions = strong overall interactions, limited sharing of electrons between any two atoms = weak bonds between individual atoms

Band Theory - overlap of half-filled 4s orbitals of large number of Cu atoms results in a half filled valence band, electrons that move from the filled half to the empty, slightly higher energy upper half are free to migrate from one empty orbital to another

Crystalline Solid - has a well-defined, ordered structure in three dimensions

Amorphous Solid - has a disordered structure

Crystal Lattice - geometric arrangement of lattice points in a crystal

Unit Cell - the smallest boxlike unit for constructing a crystal by stacking the units in three dimensions

Hexagonal Closest Packed [hcp] - A crystal structure in which the layers of atoms or ions have an a-b-a-b-a-b stacking pattern

Cubic Closest Packed [ccp] - A crystal structure in which the layers of atoms, ions, have an a-b-c-a-b-c-a-b-c stacking pattern

Coordination Number - the number of other particles each particle is in contact with [for ions it is the number of oppositely charged ions an ion is in contact with]

Higher coordination number means _ interaction, therefore attractive forces holding the crystal together - Higher coordination number means MORE interaction, therefore STRONGER attractive forces holding the crystal together

Packing efficiency - the percentage of volume in the unit cell occupied by particles

The higher the coordination number, the _ efficiently the particles are packed together - The higher the coordination number, the MORE efficiently the particles are packed together

Simple Cubic Unit Cell - Atom at each corner, 1 atom in total

Body centered Cubic Unit Cell [bcc] - Atom at each corner and 1 in the middle, 2 atoms in total

Face centered Cubic Unit Cell [fcc] - Atom at each corner and 1/2 on each face, 4 atoms in total

Alloy - Metallic material that blends atoms of a host metal with atoms of one or more other elements to change the properties of the host metal

Ores - Naturally occuring compounds or mixtures of compounds from which elements can be extracted

Homogenous Alloys - Solid solution in which atoms of host and added elements are randomly and uniformly distributed

Heterogenous Alloys - Matrix of host metal atoms with “islands” of atoms of added elements interspersed

Substitutional Alloys - Atoms of added elements replace host metal in crystal lattice [form between metals of similar radii]

Ionic Solids - Monoatomic or polyatomic ions held together by ionic bonds, most are crystalline

Octahedral Holes - 6 coordination points, 1 center within, 12 edges

Tetrahedral Holes - 4 coordination points, 8 locations within

Cubic Holes - 8 coordination points, 1 center within