Solid state Physics

BONDING

• PRIMARY BONDING• IONIC BONDING• COVALENT BONDING• METALLIC BONDING

• SECONDARY BONDING• VAN DER WAAL

BONDING• DISPERSION BINDING

Electrons and Chemical Bonds

All chemical bonding is due to forces between electrostatic charges.

Covalent bonding: A pair of electrons is shared between two nonmetal atoms, allowing each atom to have access to enough electrons to fill its outer shell. Except for hydrogen, this usually means 8 electrons in the outer shell (octet rule).

Ionic bonding: One or more valence electrons of a metal atom are “stolen” by a nonmetal atom, leaving a positive metal ion and a negative nonmetal ion, which then attract one another.

Metallic bonding: Valence electrons of metals flow freely throughout a metal object. These delocalized electrons are attracted to the nuclei of the atoms through which they are moving about. This produces a strong binding force that holds the atoms together. In an iron bar, for example, there is no covalent or ionic bonding. Metallic bonding hold the metal together.

FREE ELECTRON THEORY

• POSTULATES OF CLASSICAL FREE ELECTRON THEORY

• RELAXATION TIME• COLLISION TIME • CONDUCTIVITY OF METALS• OHM’S LAW VERIFICATION• WEIDEMANN FRANZ LAW

POSTULATES

• ELECTRON GAS• ELECTRON – ION INTERACTION• ELECTRON – ELECTRON INTERACTION• MAXWELL BOLTZMANN DISTRIBUTION• MEAN FREE PATH- AVERAGE DISTANCE

TRAVELLED BY THE ELECTRON BETWEEN TWO SUCCESSIVE COLLISIONS

• TIME BETWEEN TWO SUCCESSIVE COLLISIONS

WEIDEMANN – FRANZ LAW

• The ratio of the thermal conductivity and the electrical conductivity at a given temperature for all metals is a constant. •Lorentz number ‘L’•The variation in L at the temperature ranges can be explained by taking into account the functional dependence of mean free path on temperature

QUANTUM FREE ELECTRON THEORY

• SOMMERFIELD MODEL• PARTICLE IN A BOX• IN THREE DIMENSIONS• DENSITY OF STATES• FERMI DIRAC STATISTICS• FERMI SPHERE• FERMI RADIUS• LORENTZ NUMBER• CONCLUSION

MAGNETISM•PROPERTIES OF MAGNETIC MATERIALS•LANGEVIN’S THEORY OF DIAMAGNETISM•LANGEVIN’S THEORY OF PARAMAGNETISM•CURIE TEMPERATURE•WEISS THEORY•CURIE – WEISS LAW•HEISENBERG’S THEORY •EXCHANGE INTEGRAL •ANTIFERROMAGNETISM. NEEL TEMPERATURE

• Each electron in an atom has two magnetic dipole moments associated with it, one for spin, and one for orbit. Each is a vector.

• These two dipole moments combine vectorially for each electron.

• The resultant vectors from each electron then combine for the whole atom, often canceling each other out.

• For most materials the net dipole moment for each atom is about zero.

• For some materials each atom has a nonzero dipole moment, but because the atoms have all different orientations, the material as a whole remains nonmagnetic.

• Ferromagnetic materials, like iron, are comprised of atoms that each have net dipole moment. Furthermore, all the atoms have the same alignment, at least within very tiny regions called domains. The domains can have different orientations, though, leaving the iron nonmagnetic except when placed in an external field.

• Permanent magnets are produced when the domains in a ferromagnetic material are aligned.

Materials and Magnetism