Question

(1) DEFINE THESE IN SHORT

A. CRYSTALLINE SOLID

B. AMOROPHOUS SOLID

C. MOLECULAR SOLID

D. IONIC SOLID

E. METALLIC SOLID

F. COVALENT OR NETWORK SOLID

G. CRYSTAL LATTICE

H. BRAVAIS LATTICE

I. PRIMITIVE UNIT CELL

J. CENTERED UNIT CELL

K. BODY CENTERED UNIT CELL

L. FACE CENTERED UNIT CELL

M. END CENTERED UNIT CELL

Answer 1

A.Crystalline solid.
The solids which have repetitive arrangement of atoms and molecules in a regular formation are better known as crystalline solids. These have long range order as these can extend for massiveness of the structure. As these solids having low potential energy they are always considered as the most stable form of solids.

B.Amorphous solid.
Amorphous solid, any noncrystalline solid in which the atoms and molecules are not organized in a definite lattice pattern. Such solids include glass, plastic, and gel.

C. Molecular solid.
Molecular solids are solids that are essentially collections of molecules held together by intermolecular forces (IMFs). The solid structure is maintained by IMFs rather than bonds (metallic, covalent, or ionic). The forces holding the solids together are much weaker than for other types of solids.

D.Ionic solid.
Ionic solids are solids held together by ionicbonds. They are lattices composed of oppositely charged ions. Ionic solids tend to have high melting points ("high" generally being higher than metallic but lower than covalent).

E.Metallic solid.
Metallic solids are solids composed of metal atoms that are held together by metallic bonds. These bonds are like huge molecular orbitals that span across the whole solid. This means the electrons in metallic solids are delocalized. They are not just held between a couple of atoms in a sigma bond.

F.Covalent or network solid.
A network solid or covalent networksolid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a networksolid there are no individual molecules, and the entire crystal or amorphous solid may be considered a macromolecule.

G.Crystal lattice.
Crystal lattice is - the arrangement of atoms, molecules, or ions of a crystal in the form of a space lattice.

H.Bravais lattice.
Bravais lattice, is any of 14 possible three-dimensional configurations of points used to describe the orderly arrangement of atoms in a crystal. Each point represents one or more atoms in the actual crystal, and if the points are connected by lines, a crystal lattice is formed; the lattice is divided into a number of identical blocks, or unit cells, characteristic of the Bravais lattices. The French scientist Auguste Bravais demonstrated in 1850 that only these 14 types of unit cells are compatible with the orderly arrangements of atoms found in crystals.

I.Primitive unit cell.
A primitive cell is a unit cell that contains exactly one lattice point. It is the smallest possible cell.

J.Centered unit cell.
The unit cells in which the constituent particles are present at corners as well as at some other positions in the unit cell are called as non primitive or centred unit cells
K.Body centered unit cell.
The body-centered cubic unit cell is the simplest repeating unit in a body-centered cubic structure. Once again, there are eight identical particles on the eight corners of the unit cell. However, this time there is a ninth identical particle in the center of the body of the unit cell.

L.Face centered unit cell.
The face-centered cubic unit cell also starts with identical particles on the eight corners of the cube. But this structure also contains the same particles in the centers of the six faces of the unit cell, for a total of 14 identical lattice points.

M.End centered unit cell.
If one constituent particle lies at the centre of any two opposite faces besides the particles lying at the corners, it is known as End-Centred Unit Cell. It is also known as base-centred unit cell.