NEET Chemistry Notes Solid State – Magnetic Properties of Solids
Magnetic Properties of Solids
Magnetic Properties of Solids
Every substance has some magnetic properties associated with it. The origin of these properties lies in the electrons. Each electron in an atom behaves like a tiny magnet. Its magnetic moment originates from two types of motions (i) its orbital motion around the nucleus and (ii) its spin around its own axis. Electron being a charged particle and undergoing these motions can be considered as a small loop of current which possesses a magnetic moment. Thus, each electron has a permanent spin and an orbital magnetic moment associated with it. Magnitude of this magnetic moment is very small and it is measured in the unit called Bohr magneton, pB. It is equal to 9.27x 10-24 Am2. Solids can be divided into different classes depending on their response to magnetic field.
- Diamagnetic Substances
These axe weakly repelled by the magnetic field and do not have any unpaired electron. e.g.Ti02, V205, C6 H6,NaCl, etc.
- Paramagnetic Substances
These are attracted by the magnetic field and have unpaired electrons. These lose magnetism in the absence of magnetic field.
e.g. 02, Cu2+, Fe3+, etc
- Ferromagnetic Substances
These are attracted by the magnetic,field and show permanent magnetism even in the absence of magnetic field, e.g. Fe, Co and Ni, etc.
- Antiferromagnetic Substances
These substances have net magnetic moment zero due to compensatory alignment of magnetic moments, e.g. MnO, Mn02, Mn20, FeO, etc.
- Ferrimagnetic Substances
These substances have a net dipole moment due to unequal parallel and antiparallel alignment of magnetic moments, e.g. Fe304, ferrites, etc.
Dielectric Properties of Solids
These are seen in insulators. Insulators show generation of dipoles in them, when they are placed in an electric field.
These dipoles are given below:
- May align themselves in an ordered manner so that there is ; a net dipole moment in the crystal.
- May align themselves in such a manner that dipole moments may cancel each other.
- It is also possible that there are no dipoles in the crystal but only ions are present.
- Piezoelectricity It is produced by applying mechanical stress on polar crystals.
- Pyroelectricity It is produced on heating some polar crystals.
- Ferroelectricity Piezoelectric crystals with permanent dipoles are said to have ferroelectricity, e.g. BaTi03, KH2P04, etc. All ferroelectric solids are piezoelectric but all piezoelectric solids are not ferroelectric, e.g. quartz is piezoelectric but not ferroelectric.
- Antiferroelectricity In antiferroelectric crystals, the dipoles in alternate polyhedra point up and down in such a way that the crystal does not possess any net dipole moment.
- Superconductivity The phenomenon, where electricity passes through a material without resistance is called superconductivity and the material is known as superconductor, e.g. Hg acts as superconductor at 4 K. Electrical conductivity of semiconductors and electrolytic conductors increases with increase in temperature while in case of superconductors and metallic conductors it decreases with increase in temperature.