Physics M7

the most stable arrangement of the molecules of solids is

• the one with the minimum potential energy of the interaction forces

• the one with minimum kinetic energy of the interaction forces;

• the one with maximum potential energy of the interaction forces.

The molecules of solids:

• interact through electromagnetic van der Waals forces;

• interact through magnetic forces;

• interact through electrical forces.

Crystal lattices consist of:

• identical tiny boxes (unit cells) that fill the space of the lattice;

• b. different tiny boxes (unit cells) that fill the space of the lattice;

• identical big boxes (unit cells) that cannot fill the space of the lattice.

Long-range order is:

• when the arrangement of the unit cells is continuous and unbroken at distances, much larger than the distances between molecules;

• when the arrangement of the unit cells is continuous and broken at distances, much larger than the distances between molecules;

• when the arrangement of the unit cells is continuous and unbroken at distances, much smaller than the distances between molecules.

Short-range order is:

• when the crystal lattice is unbroken for small distances only;

• when the crystal lattice is broken for small distances only;

• when the crystal lattice is unbroken for larger distances only.

Monocrystals are:

• anisotropic;

• isotropic;

• metastable.

Polycrystals are:

• anisotropic;

• isotropic;

• metastable.

Polymorphism is:

• when a solid material can exist in more than one form of crystal lattice;

• when a solid material cannot exist in more than one form of crystal lattice;

• not valid for the solid materials.

The molecular crystal lattice is composed of molecules, interacting by:

• weak van der Waals forces;

• strong van der Waals forces;

• covalent chemical bonds.

Nematic liquid crystals have:

• long-range orientational order and no positional order;

• short-range orientational order and positional order;

• long-range positional order and no orientational order.