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