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# Assignment 1

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Elements of crystal
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# Assignment 1

Solid state for degree students

Solid state for degree students

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### Assignment 1

1. 1. Dr Shelma R Assistant Professor KSMDB College, Sasthamcotta
2. 2. Crystalline state  A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.
3. 3. Isotropy and anisotropy  Iso means same and tropic means direction  when the properties of a material are the same in all directions, the material is said to be isotropic  When the properties of a material vary with different crystallographic orientations, the material is said to be anisotropic.
4. 4. External features of crystal  Face: crystal face One of the relatively flat surfaces by which a crystal is bounded. Like face Unlike face
5. 5. Symmetry  When the faces of a crystal can be arranged in a repetitive and regular pattern around the center of the crystal, the crystal has symmetry  Crystals have an ordered internal arrangement of atoms. This ordered arrangement shows symmetry  The atoms are arranged in a symmetrical fashion on a three dimensional network referred to as a lattice.
6. 6. Elements of symmetry:  A geometrical entity such as a line (or axis),a plane or a point with respect to which one or more symmetry operations may be carried out is called a symmetry element.  A crystal possess following three types of symmetry  Plane of symmetry, axis of symmetry and centre of symmetry
7. 7. Plane of symmetry  It is an imaginary plane which passes through the centre of a crystal can divides it into two equal portions which are exactly the mirror images of each other.
8. 8. Axis of symmetry  An axis of symmetry or axis of rotation is an imaginary line, passing through the crystal such that when the crystal is rotated about this line, it presents the same appearance more than once in one complete revolution i.e., in a rotation through 360°.  Suppose, the same appearance of crystal is repeated, on rotating it through an angle of 360°/n, around an imaginary axis, is called an n-fold axis where, n is known as the order of axis. By order is meant the value of n in so that rotation through gives an equivalent configuration.
9. 9. Thank You......