Students can go through TS Inter 2nd Year Chemistry Notes 1st Lesson Solid State will help students in revising the entire concepts quickly.
TS Inter 2nd Year Chemistry Notes 1st Lesson Solid State
→ Solids are of two types. They are crystal-line solids and amorphous solids.
→ Crystalline solids are of four types. They are :
- Covalent solid
- Ionic solid
- Molecular solid and
- Metallic solid.
→ Depending on the type of attractive forces between molecules the molecular solids are again categorised into three types :
- Non – polar molecular solids: In which atoms such as Ar, Kr, Xe etc., or molecules of covalent compounds are held together by weak van der Waal’s forces. These solids have low m.pts and the particles are widely separated than in close packed ionic or metallic lattices.
- Polar molecular solids: In which molecules are held together by relatively stronger dipole-dipole interactions. These solids are soft and non – conductors of electricity. Their m.pts are higher than those of non – polar molecular solids e.g., solid CO2.
- Hydrogen bonded molecular solids : are those in which molecules participate in hydrogen bonding. In crystals of benzoic acid, hydrogen bonds cause the association into dimers which are then held together van der Waal’s forces. These are also non – conductor of electricity.
→ The smallest repetitive unit of a crystal lattice which is used to describe the lattice is called the unit cell. Crystals possess the same symmery as their constituent unit cells.
→ In a simple or primitive cubic lattice the lattice points are located at the corners of each unit cell and can contribute only 1/8 of each particle at the corner to the unitj cell shared by unit cells in space lattice, So a simple cubic unit cell has particle per unit cell.
→ In a body centred cubic unit cell particles are located at the centre of the ceil as well as at the corners.
8 (at corners) × \(\frac{1}{8}\) + 1 (at body centre) × 1
= 2 particles.
→ In a face centred cubic unit cell atoms are found at the centre of the six faces of the cell as well as at each of the eight corners. The number of particles per unit cell in fee is
6 (at centre of each face) × \(\frac{1}{2}\) + 8 (at corners) × \(\frac{1}{8}\) (at comers) = 4 particles.
→ In hep and ccp structures the coordination number i.e., the number of surrounding atoms in contact with atom is 12.
→ The void created when six spherical particles are contact with each other is called octahedral void or octahedral hole.
→ The void created when four spherical particles are in contact with each other called tetrahedral void or tetrahedral hole.
→ In a close packed structure of N atoms there are 2N tetrahedral voids and N octahedral voids because the octahedral voids are larger than tetrahedral voids.
→ When X – rays are incident on a crystal face, they are reflected by the atoms in different planes.
→ Bragg’s equation is useful to calculate the distance between the repeating planes of particles in crystals from the reflected x – rays. It is, nλ = 2d sin θ where n is an integer like 1, 2, 3 and represents order of reflection, λ is the wavelength of the x – rays used and d is the distance between the repeating places.
→ A Schottky defect consists of a pair of holes in the crystalline lattice due to the absence of one positive ion and one negative ion.
→ Frenkel defect is created when an ion occupies an interstitial site instead occupying its correct lattice site.
→ The metal excess defect is due to the absence of a negative ion from its lattice site leaving a hole which is occupied by an electron, there by maintaining the electrical balance.
→ The solids having F – centres have colour and the intensity of the colour increases with increase in the number of F – centres.
→ Metal excess defects also occurs when an extra positive ion occupies an interstitial position in the lattice and to maintain ele-ctrical neutrality one electron is included in an interstitial position e.g. ZnO, CaO, Cr2O3 and Fe2O3.
→ The solids with metal excess defect contain free electrons and behave as n – type semi-conductor.
→ Metal deficiency defect is due to the absence of a positive ion from its lattice point and the charge can be balanced by an adjacent metal ion having an extra positive charge e.g. FeO, NiO, FeS and Cul.
→ Crystals with metal deficiency defects are p – type semiconductors.
→ Doping is a process of mixing pure silicon or germanium with an impurity.
→ n-type semiconductors (n – stands for negative) are obtained due to metal excess defect or by adding trace amounts of V or 15th group elements (P, As) to pure silicon or germanium.
→ p-type semiconductors (p – stands for positive) are obtained due to metal defi-ciency defect or by doping with impurity atoms containing less electrons (i.e., atoms of III or 13th group).
→ Diamagnetic solids contain paired electrons (↑↓) and repel the external magnetic field.
→ Paramagnetic solids contain unpaired electrons and are attracted into the applied magnetic field.
→ In ferromagnetic solids there occurs mag-netic interaction between the neighbouring centres (domains) and the electrons in these centres interact in parallel direction (↑↑↑↑↑). This interaction leads to an increase in magnetic moment. Iron, cobalt and nickel are ferromagnetic substances.
→ In antiferromagnetic solids there occurs magnetic interaction between the neigh-bouring centres and the electrons in these centres interact in antiparallel (↑↓ ↑↓ ↑↓) direction which leads to a decrease in magnetic moment e.g., [Cu(CH3COO)– H2O]2;
VO (CH3COO)2, MnO, MnO2, Mn2O3.
→ In ferrimagnetic solids there occurs mag-netic interactions between the neighbou-ring centres and the electrons in these cen-tres interact in such a way which leads to the presence of uncompensated spins (↑↑↓↑↑↓) in the opposite direction resulting some magnetic moment e.g. magnetite (Fe3O4); ferrite M FeO4 (where M = Mg2+, Cu , Zn2+ etc.)