Unit 5
Solid State Physics
Crystal Structures and Bonding in Solids
, Matter
Gases -
• The average distance between molecules is large compared to their size
• Intermolecular forces are small compared to the binding forces.
• Because of this relative positions of molecules are completely random.
Liquids -
Condensed systems
• The atoms and molecules in condensed systems are close together
• The intermolecular forces are comparable to the binding forces between the molecules.
• Short range forces between the molecules can be continuously broken by the high
thermal energy.
Solids -
• When the liquid is slowly cooled, the molecules will arrange themselves in a crystalline
array that produces the maximum number of bonds and thereby leads to a state of
minimum energy.
• When the liquid is cooled too fast, the internal energy will be removed before the
molecules have a chance to arrange themselves forming a solid – a snapshot of the
liquid.
, Crystal structures
A crystalline solid is a three-dimensional, periodic array of atoms or molecules
called a crystal structure. The most convincing evidence concerning the regular
arrangement of atoms in a solid comes from X-ray diffraction. The diffraction
pattern not only confirms the periodic arrangement, but also has allowed
crystallographers to determine the arrangement.
Crystal structure can be specified by a periodic space lattice and an atom or
group of atoms placed at or around each lattice point. The atom or group of
atoms constitutes the basis (see Fig).
The space lattice is a
regular periodic
arrangement of
points in space and is
purely a
mathematical
abstraction (see Fig).
To obtain a crystal structure, we must place at or around each lattice point a
basis of atoms, Fig. 22-lc. This group of atoms must be identical in
composition, arrangement, and orientation.
Solid State Physics
Crystal Structures and Bonding in Solids
, Matter
Gases -
• The average distance between molecules is large compared to their size
• Intermolecular forces are small compared to the binding forces.
• Because of this relative positions of molecules are completely random.
Liquids -
Condensed systems
• The atoms and molecules in condensed systems are close together
• The intermolecular forces are comparable to the binding forces between the molecules.
• Short range forces between the molecules can be continuously broken by the high
thermal energy.
Solids -
• When the liquid is slowly cooled, the molecules will arrange themselves in a crystalline
array that produces the maximum number of bonds and thereby leads to a state of
minimum energy.
• When the liquid is cooled too fast, the internal energy will be removed before the
molecules have a chance to arrange themselves forming a solid – a snapshot of the
liquid.
, Crystal structures
A crystalline solid is a three-dimensional, periodic array of atoms or molecules
called a crystal structure. The most convincing evidence concerning the regular
arrangement of atoms in a solid comes from X-ray diffraction. The diffraction
pattern not only confirms the periodic arrangement, but also has allowed
crystallographers to determine the arrangement.
Crystal structure can be specified by a periodic space lattice and an atom or
group of atoms placed at or around each lattice point. The atom or group of
atoms constitutes the basis (see Fig).
The space lattice is a
regular periodic
arrangement of
points in space and is
purely a
mathematical
abstraction (see Fig).
To obtain a crystal structure, we must place at or around each lattice point a
basis of atoms, Fig. 22-lc. This group of atoms must be identical in
composition, arrangement, and orientation.
