TYPES OF SOLIDS

The Final Condensed State of Matter -

Solids • As you know, solids

have maximum

intermolecular forces

• When illustrating

solids, molecules,

atoms, or ions can be

modeled by spheres

• There are two main

groups of solids:

• Crystalline

• Amorphous

What is a Crystalline Solid?

• In a crystalline solid, particles are in a rigid, highly ordered 3-D arrangement

• Atoms, molecules, or ions occupy specific (predictable) positions called lattice points

• These particles pack themselves in such a way that most efficiently uses the available space • Called close packing

• We rationalize maximum intermolecular force in a solid crystal by the close packing of the spheres

Lattice Points and the Unit Cell in a

Crystalline Solid • Basic repeating

structural unit of a

crystalline solid is called

a unit cell

• Lattice points in a unit

cell are considered to be

at the nuclei of the

atoms making up the

unit cell

The Three Basic Types of Unit Cells

Types of Crystalline Solids – Ionic Solids

• Lattice points occupied by cations and anions

• Structure can be explained by the closest packing of ionic spheres • Packing is done in a way that maximizes the attractions

and minimizes repulsions between the ions

• Crystal is held together by intramolecular electrostatic attraction • Ion-ion interactions

Physical Properties of Ionic Solids

• Hard and brittle

• High melting and boiling points

• Testament to the strength of the ionic bonds

• Remember, strength of ionic bonds depends on the charges and sizes of the

ions as given by Coulomb’s Law:

Lattice Energy = k(Q`Q2

r)

• So, small and highly charged ions form strong, favorable ionic compounds!

• Poor conductor of heat and electricity

• Insulators

• Many are water soluble

• Aqueous solutions conduct electricity

Types of Crystalline Solids – Molecular

Solids • Lattice points occupied by molecules

• Molecules themselves are held together by intramolecular

covalent bonding

• Crystal is held together by intermolecular forces

• For nonpolar covalent molecules - London dispersion forces

• For polar covalent molecules - Dipole-dipole and hydrogen

bonds

• Examples:

• Ice (solid water)

• Dry ice (solid carbon dioxide)

Physical Properties of Molecular Solids

• Fairly soft

• Low to moderate melting points

• Poor electrical and thermal conductors

• Insulators

Types of Crystalline Solids – Covalent

Network Solids • Lattice points occupied by nonmetal atoms

• Crystal itself is held together by strong intramolecular

directional covalent bonds

• Examples:

• Graphite (C, s)

• Diamond (C, s)

• Quartz (SiO2)

Covalent-Network Solids – Diamond

• Diamonds are an example of a covalent-

network solid in which atoms are covalently

bonded to each other

• They tend to be hard and have high melting points

Covalent-Network Solids - Graphite

• Graphite is an example of a covalent-network AND

molecular solid

• Carbon atoms are covalently bonded to each other

• Atom layers are held together with van der Waals forces

• Graphite tends to be softer and have lower melting points than

diamond; however, it is a good conductor of electricity along

the layers due to the delocalized pi bond system

Physical Properties of Covalent-Network

Solids • Hard

• High melting points

• Poor electrical and thermal conductors (usually)

Types of Crystalline Solids – Metallic

Solids • Lattice points occupied by

metal atoms

• Metals are not covalently bonded, but the attractions between atoms are too strong to be van der Waals forces • Valence electrons are

delocalized throughout the solid

• This delocalization of electrons is referred to as the “Electron Sea Model”

• Attraction between positive cores and a sea of valence electrons resulting in bonding that is non-directional in nature

Physical Properties of Metallic Solids

• Malleable

• Ductile

• Good electrical and thermal conductors

• Wide range of hardness

• Wide range of melting points

• Although, many do have HIGH melting points

Summary of the Types of Bonding in

Crystalline Solids

The Other Types of Solids • Amorphous

• No particular order in the

arrangement of particles

• No lattice points!

• Examples

• Glass

• Inorganic materials

that have cooled to a

rigid state without

crystallizing