types of solids - waterford of the types of bonding in crystalline solids . the other types of...
TRANSCRIPT
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