solid state

R.JOTHI

• DMI

College of Education Palanchoor, Nazarethpet

POWER POINT PRESENTATION

SOLID STATE

Signature of the Teacher Trainee Signature of the Lecturer

SOLID STATE

INTRODUCTION: Solids are characterized by incompressibility, rigidity and mechanical strength.Solids are usually classified as either 1.Crystalline solids2.Amorphous solids

1.CRYSTALLINE SOLIDS:Crystalline solids have definite and ordered arrangement of the constituents extended over a long distance and is called a long-range order. They possess a sharp melting point.:2.AMORPHOUS SOLIDSAmorphous solids like glass, rubber etc., although possessing many characteristicsof crystalline solids such as definite shape, rigidity and hardness, but are devoidof a regular internal structure and melt gradually over a range of temperature. Forthis reason they are not considered as true solids but rather highly supercooledliquids

CRYSTALLOGRAPHY:A study of internal structure of crystals. 1913 – English physicists, Father and Son, William and Lawrence Bragg developed X-ray crystallography further by establishing laws that govern the orderly arrangement of atoms in crystal interference and diffraction patterns. They also demonstrated the wave nature of X-rays. In 1915 William Bragg and Lawrence Bragg were awarded Nobel prize for physics for X-ray analysis of crystal structure.

UNIT CELL:Unit cell is the smallest fundamental repeating portion of a crystal latticefrom which the crystal is built by repetition in three dimension.Types of Cubic System Simple cubic Body centred cubic Face centred cubic

X-RAYS AND CRYSTAL STRUCTUREX-rays are electromagnetic waves of very short wavelength. The wave natureof X-rays is not confirmed by diffraction experiment, because a grating of about40 million ruling per cm is required for diffraction experiment. The preparation ofsuch a grating is highly impossible.

BRAGG’S EQUATIONW.L.Bragg and W.H.Bragg derived a mathematical relation to determineinteratomic distances from X-ray diffraction patterns. The scattering of X-rays by crystals could be considered as reflection from successive planes of atoms in the crystals. However, unlike reflection of ordinary light, the reflection of X-rayscan take place only at certain angles which are determined by the wavelength ofthe X-rays and the distance between the planes in the crystal. The fundamentalequation which gives a simple relation between the wavelength of the X-rays,the interplanar distance in the crystal and the angle of reflection

BRAGG’S EQUATIONBragg’s equation is nλ = 2d sinθwhere n is the order of reflectionλ is the wavelength of X-raysd is the interplanar distance in the crystalθ is the angle of reflection

SIGNIFICANCE OF BRAGG’S EQUATION If we use X-rays of known wavelength (λ), then the interatomic distance (d) in an unknown crystal can be calculated, crystal whose interatomic distance ‘d’ is known, then the wavelength of X-rays can be calculated.

BRAGG’S SPECTROMETER METHODThis method is one of the important method for studying crystals using X-rays. The apparatus consists of a X-ray tube from which a narrow beam of X-rays is allowed to fall on the crystal mounted on a rotating table.The rotating table is provided with scale and vernier, from which the angle of incidence, θ can be measured.

TYPES OF CRYSTALSCrystals are classified into the following four types depending upon thenature of the units which occupy the lattice points.1. Molecular Crystals 2. Covalent Crystals3. Metallic Crystals 4. Ionic Crystals

Molecular CrystalsThe lattice points in molecular crystals consist of molecules which do not carry any charge. The forces binding the molecules together are of two types a.Dipole-dipole interaction b.Vanderwaal’s forces

Dipole-dipole forces occur in solids which consists of polar molecules e.g., ice. The Vanderwaal’s forces are more general and occur in all kinds of molecular solids.

Covalent CrystalsThe lattice in covalent crystals consists of atoms linked together by acontinuous system of covalent bonds. Diamond is a good example for this type

Metallic CrystalsMetallic crystal consists of an assemblage of positive ions immersed in a sea of mobile electrons. The force that binds a metal ion to a number of electrons within its sphere of influence is known as metallic bond. This force of attraction is strong and is thus responsible for a compact solid structure of metals.

Ionic CrystalsIn ionic crystals, the units occupying lattice points are positive and negative ions. Each ion of a given sign is held by coulombic forces of attraction to all ions of opposite sign. The forces are very strong.

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