Chemistry

### DEFINITION

=> PSEUDO SOLIDS OR SUPER COOLED SOLIDS : Amorphous solids like liquids have tendency to flow that's why they are called pseudo solids or super cooled liquids.

=> ANISOTROPY: It is the property shown by crystalline solids in which their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystals. This is due to the different arrangement of particles in different directions.

=> ISOTROPY: This is the characteristic property of amorphous solids which show same physical property along any direction.

=> MOLECULAR SOLIDS:Molecules are the constituent particles of molecular solids.

=> NON-POLAR MOLECULAR SOLIDS: (i) These solids comprise of either atoms or the non-polar molecules.
(ii) e.g. Ar, He, H_2, Cl_2, I_2 etc.

=> POLAR MOLECULAR SOLIDS:(i) Polar molecules are the constituent of solids.

(ii) e.g. HCl, SO_2, NH_3 etc
=> IONIC SOLIDS: Ions are the constituent particles of ionic solids.

=> METALLIC SOLIDS:In metallic solids, positive ions are surrounded by and held together by a sea of free electrons.

=> COVALENT OR NETWORK SOLIDS:(i) These solids are formed by the formation of covalent bonds between adjacent atoms. These atoms are non-metal.
(ii) Also called giant molecules.

=> CRYTSAL LATTICE:The diagrammatical representation of three dimensional arrangement of constituent particles in a crystal is called crystal lattice. In this each particles is depicted as a point.

=> BRAVIAS LATTICE:Bravias Lattices : There are only 14 possible three dimensional lattices. These are called Bravias Lattice.

=> LATTICE POINT:Each point in a lattice is called lattice point or lattice site.

=> UNIT CELL:It is the smallest portion of a crystal lattice. Repetition of this unit cell in different directions generates the entire lattice.

=> PRIMITIVE UNIT CELL : In this, constituent particles are present only on the corner positions of a unit cell.

=> CENTRED UNIT CELL : In this unit cell, constituent particles are present at positions other than corners.

=> BODY-CENTRED UNIT CELLS : In this one constituent particle is present at its body centre besides the one present at the corners.

=> FACE-CENTRED UNIT CELLS: In this, one constituent particle is present at the centre of each face besides the one present at the corners.

=> END-CENTRED UNIT CELLS : In this, one constituent particle is present at the centre of any two opposite faces besides the one present at the corners.

=> PACKING EFFICIENCY:It is the percentage of total space filled by the particles.

=> DEFECTS:These are basically irregularities in the arrangement of constituent particles. Defects are of two types which are point defects and line defects.

=> POINT DEFECTS:This is the deviation from ideal structure around a point or atom in a solid.

=> LINE DEFECTS : This is the deviation from ideal structure in entire rows or lattice points. These irregularities are called crystal defects.

=> STOCHIOMETRIC DEFECTS:In this, Stoichiometry of the solid does not change. They are called intrinsic or thermodynamic defects.

=> VACANCY DEFECT:(i) Vacancy Defect : This is due to the vacancy present in the crystal. Due to this, density of crystal decreases. This defect can develop when a substance is heated.

=> INTERSTITIAL DEFECT : In this, some constituent particles occupy an interstitial site. Due to this defect, density of the substance increases.

=> FRENKEL DEFECT:In this, smaller ion (usually cation) is dislocated from its normal site to an interstitial site.

=> SCHOTTKY DEFECT:In order to maintain electrical neutrality,
The no. of missing cations = no. of missing anion

=> CONDUCTORS : They have conductivity range from 10^4 - 10^7 ohm^(-1) m^(-1).

=> INSULATORS : They have conductivity range from 10^(-20) - 10^(-10) ohm^(-1) m^(-1).

=> SEMICONDUCTORS : They have conductivity range from 10^(-6) -10^(4) ohm^(-1) m^(-1).

=>DOPING:Conductivity of intrinsic semiconductors is increased by adding an appropriate amount of suitable impurity. This process is called doping.

=> DIODE : A combination of n-type and p-type semiconductors and used as a rectifier.

=> TRANSISITORS : A combination made by sandwiching one type of semiconductor between two layers of other type of semiconductor. npn or pnp type of transistors are used for detecting or amplifying radio or audio signals.

=> PHOTODIODE : Used for conversion of light energy into electrical (solar cell) energy.