# Magnetic properties Chemistry Notes

## Magnetic properties Chemistry Notes

→ Metallic solids behave differently in the presence of magnetic field. On the basis of magnetic properties, substances can be classified in to following five classes

→ Diamagnetic Substances : Those substances which are weakly repelled by external magnetic field are called diamagnetic substances. Their orbitals are fully filled i.e, no unpaired electrons are present. As a result, magnetic moment possessed by one electron having spin in one direction is neutralized by other electron having spin in opposite direction Examples: Zn2+ compound, TiO2, NaCl, C6H6V2O3, Mg2+ etc.

→ Paramagnetic Substances : Those substances which are attracted weakly by external magnetic field are called paramagnetic substances This property is shown by those substances which have unpaired electrons. These substances lose their magnetism in the absence of magnetic field. Examples: Some transition elements and ions
like Cu2+, Fe3+, TiO, VO2, Cuo, CuCl2 etc

→ Ferromagnetic substances : Those substances which are attracted strongly by external magnetic field and exhibit permanent magnetism even in the absence of magnetic field, are called ferromagnetic substances. Example : Fe, Co, Ni, CrO2 etc.

→ Magnetic moment of unpaired electrons in ferromagnetic substances are oriented in one direction As a result, ferromagnetism is produced in them.

→ Ferrimagnetic Substances : Those substances which are expected to possess strong magnetism due to presence of unpaired electrons but in fact magnetism are called ferrimagnetic substances. Magnetic moments are unevenly aligned as parallel and anti-parallel. As a result, these have same net dipole moment. Example: Fe3O4 (magnetite), ferrite (Mg Fe2O4 or Zn Fe2 O4) etc. These substances lose their small magnetism on heating

→ Anti Ferromagnetic Substances : In such type of substances it is assumed that the presence of paramagnetism or ferromagnetism is due to presence of unpaired elections, but these have zero dipole moment. It these substances, parallel and anti-parallel magnetic moments of electrons balance each other. Example: MnO, Mn2O3, MnO4,V2,O3, Fe2 O3, FeO etc.

Chapter in Brief and Glossary :

• Solid : Their mass, volume and shape are definite. This is due to fixed position of particles, short distance between them and strong interactions.
• Crystalline Solid : The arrangement of constituent particles in it is of long range. It has definite melting point and is anisotropic in nature.
• Amorphous Solid : The arrangement of constituent particles in it is of short range. It has indefinite melting point. It is isotropic in nature. It is called super-cooled liquid.
• Crystal Lattice : The regular arrangement of constituent particles (lattice points) of a crystalline solid in three-dimension space is called crystal lattice.
• Lattice Point: The points at which constituent particles are arranged, are called lattice points.
• Bravais lattices : The possible lattices of fourteen different types are called Bravais lattices.
• Unit Cell : The smallest characteristic part of lattice which when repeated over and over again to form lattice, is called unit cell.
• Simple Unit cell : In this cell, constituent particles are arranged at corners of cube only.
• Body Centred Unit Cell : In this cell, the Sonstituent particle is also present at centre of body along with at the corners of cube.
• Face Centred Unit Cell : In this cell, the constituent particles are also present at centre of faces along with at the corners of cube.
• End Centred Unit Cell : In this cell, the constituent particles are also present at centres of any two opposite faces along with corners of cube.
• Packing Efficiency : The percentage of total space filled by the particles is called packing efficiency The packing efficiency of hep or ccp or foc is 74% the packing efficiency of body centred cubic structure is 68% and the packing efficiency of simple cubic cell is 52.4%.
• Imperfections or Defects : Any departure from prefectly ordered arrangement of constituent particles is crystal is called imperfection or defect.
• Point Defect : The imperfection in ideal arrangement around a point or an atom in a crystalline substance is called point defect.
• Stoichiometric Defect: In this type of point defect, there is no effect on stoichiometry of solids. So, here the ratio of cations and anions in crystal is according to chemical formula.
• Vacancy Defect : When some lattice sites are vacant then vacancy defect is produced in crystal. It decreases the density of substance.
• Frenkel Defect: In this type of defect, an ion comes in interstitial site by displacement from its actual position.
Schottky Defect : In this type of defect, the same number of cations and anions are missing from their lattice points due to which density decreases.
• Impurity Defect : This type of defect is produced due to impurity in crystal.
• Non-Stoichiometric Defect: In this type of defect, the ratio of cations and anions is different slightly from chemical formulas of that compound. It is metal excess and metal deficient type defect.
• F-centres : The anionic vacancies filled with unpaired electrons are called F-centres or colour centres. These are responsible for producing colour in crystal.
• Conductors : The solids which conduct more amount of electricity are called conductors.
• Insulators : The solids which do not conduct electricity are called insulators.
• Semiconductors: The solid whose conductivity is in between conductors and insulators, are called semiconductors. These are of two type : intrinsic semiconductors and extrinsic semiconductors.
• Band Theory: According to this theory, atomic orbitals of atoms of metals combine to form molecular orbitals. The energy of these molecular orbitals are so close to each other that these are shown as bands.
• Forbidden Zone or Energy Gap : The vacent place present between two bands is called forbidden zone.
• Valence Band : Atomic orbitals of valency shell of metal atoms combine to form molecular orbitals and the difference in energy of these molecular orbitals is very less and these form a band, which is called valence band.
• Conduction Band: The high empty band nearer to filled valence band is called conduction band.
• Intrinsic Semiconductors: These types of semiconductors are non-conductors at room temperature but convert into semiconductors on increasing temperature. Example : Silicon and Germanium.
• Extrinsic Semiconductors: Impurity is added to increarse conductivity of semiconductor. These impure conductors are called extrinsic semiconductors. The conductivity of these substance is more than intrinsie semiconductors.
• Doping : It is a method of adding impurities in semiconductors.
• n-type Semiconductors: When elements of 15th group like P, As, Sb ete are doped with elements of 14th group then n-type semiconductors are formed.
• p-type Semiconductors: When element of 13th group like Al, Ga, In etc are doped with elements of 14th group. Then ptype semiconductors are formed.
• 12-16 Groups compounds : When compounds are formed by doping of elements of 12th group and 16th group, then these are called 12-16 groups compounds Example : Zns, Cds, Hg Te ete.
• 13-15 Groups compounds : When compounds are formed by doping of elements of 13th group and 15th group then these are called 13-15 groups compound. Example : InSb, AIP. Ga As etc.
• Diamagnetic Substances : Those substances which are weakly repelled by external magnetic field are called diamagnetic substances. These substances do not have unpaired electrons. Example: TiO2, NaCl, V2O3 etc.
• Paramagnetic Substances : Those substances which are attracted weakly by external magnetic field are called paramagnetic substances. These have unpaired electrons. Example : Tio, CuO, VO2 etc.
• Ferromagnetic Substances : Those substance which are attracted strongly by external magnetic field and show permanent magnetism even in the absence of magnetic field are called ferromagnetic substances, Example : CrO2, Ni, Co etc.
• Ferrimagnetic Substances : Those substances in which it is expected to show strong magnetism due to presence of unpaired electrons but infact they have less magnetism, are called ferri magnetic substances. Example : Fe3 O4, Mg Fe2O4 etc.
• Anti Ferromagnetic Substances : In such type of substances, it is assumed the presence of para magnetism or ferromagnetic is due to presence of unpaired electrons but these have zero dipole moment. Example: MnO, MnO4,V2O3 etc

Important Formulae :

→ Calculation of Density d = $$\frac{Z M}{(a)^{3} \mathrm{~N}_{\mathrm{A}}}$$, where Z = Number of atoms present in unit all
(ay’N ‘
d = density, M = Molar mass, a = Edge length
NA = Avogadro Number (6022 x 1023 )

→ Various Parametors of Unit cell and Important Formulae

where a = Length of edge

→ Packing Efficiency

 Crystal System Packing Efficiency Simple cubic 52.4% Body centred 68% Face centred 74% Hexagonal close packing 74% Cubic close packing 74%

→ $$\frac{r^{+}}{r^{-}}=\frac{\text { Radius of Cation }}{\text { Radius of Anion }}$$

→ Tetrahedral void

→ Octahedral void