Chemistry Answer the following in one or two sentence.

Material will be electrically neutral.

Total number of electrons in doped silicon will be more than in original silicon.

The substances which possess unpaired electrons and high paramagnetic character and when placed in a magnetic field are strongly attracted and show permanent magnetic moment even when the external magnetic field is removed are said to be ferromagnetic. They can be permanently magnetised. In the solid state, the metal ions of ferromagnetic substance are grouped together into small regions called domains, where each domain acts as a tiny magnet.

For example : Fe, Co, Gd, Ni, CrO2, etc.

In hcp and ccp crystal lattices coordination number is 12 and packing efficiency is 74%.

A solid crystalline electrolyte like NaCl is hard, brittle and electrically nonconductor. But its melt conducts electricity.

Since the energy difference between valence band and conduction band in semiconductor is not large, the electrons from valence band can be promoted to conduction by heating. Hence electrical conductivity of a semiconductor increases with temperature.

Unit cell : It is the smallest repeating structural unit of a crystalline solid (or crystal lattice) which when repeated in different directions produces the crystalline solid (lattice). The crystal is considered to consist of an infinite number of unit cells. The unit cell possesses all the characteristics of the crystalline solid.

Picture A represents metal conductor, Picture B represents insulator, Picture C represents semiconductor.

fcc has the most efficient packing of particles while scc has the least efficient packing.

The smallest constituents or particles of various solids are atoms, ions or molecules.

The uses of semiconductors are as follows :

1. They are used in transistors, digital computers and cameras.
2. They are used in solar cells and television sets.
3. By combining n-type and p-type semiconductors, n-p junctions are formed which are effectively used in rectifiers or to convert light energy into electrical energy.

There are three major classes of point defects : stoichiometric point defects, impurity defects and nonstoichiometric point defects.

There are four types of stoichiometric point defects as vacancy defect, self interstitial defect, Schottky defect and Frenkel defect.

The tetrahedral and octahedral voids occur in hep and ccp/fcc structures. There are two tetrahedral voids associated with each atom. The number of octahedral voids is half that of tetrahedral voids. Thus, there is one octahedral void per atom.

(1) Coordination number : The number of the closest neighbouring constituent particles like atoms, ions or molecules which are in contact with a particular particle or an atom in the crystal lattice is called coordination number of that particle.
(In the crystal lattice, all atoms may have same or different coordination numbers.)
(2) The magnitude of the coordination number is a measure of compactness of spheres in close-packed structures.
(3) The higher the coordination number, the closer are the spheres to each other.

(1) The constituent particles like atoms, ions or molecules of the crystal can be arranged in seven different ways changing edges (a, b, c) and angles (α, β, γ) and accordingly they form seven systems or types of the crystal.

(2) These seven crystal system are named as :
(a) Cubic system, (b) Tetragonal system (c) Orthorhombic system (d) Rhombohedral system (e) Monoclinic system (f) Triclinic system (g) Hexagonal system.

Lattice point : A position occupied by a crystal constituent particle like an atom, ion or a molecule in the crystal lattice is called lattice point or lattice site.
OR
Any point at the intersection of the lines in the unit cell occupied by a constituent particle like an atom, an ion or a molecule in the crystalline solid is called a lattice point.

Crystal lattice (space lattice) : A regular arrangement of the constituent particles (atoms, ions or molecules) of a crystalline solid having similar environment in three dimensional space is called crystal lattice or space lattice.

The characteristics of molecular crystals are as follows :

1. The constituent particles of these solids are molecules (or unbonded single atoms) of the same substance.
2. The atoms within the molecules are bonded by covalent bonds.
3. The molecules are held together by intermolecular forces of attraction.

Allotropes : When a substance exists in two or more forms then they are called allotropes. They are polymorphous. For example, carbon has allotropes diamond and graphite.

The solids in which the constituent particles are charged ions namely cations and anions held together by electrostatic force of attraction are called crystalline solids.

Crystalline solids are classified as follows :

1. Ionic crystals
2. Covalent network crystals
3. Molecular crystals
4. Metallic crystals

Polymorphous: A single substance which crystallises in two or more forms under different conditions of solidification is called polymorphous. Polymorphic forms of an element are called allotropic forms or allotropes. For example, carbon exists as diamond and graphite, or sulphur exists in rhombic and monoclinic allotropic forms.

1. Crystalline solid has long range order of regular pattern of arrangement which repeats periodically over entire crystal.
2. Within the given pattern, the arrangements of different atoms or ions or molecules is different in different directions. Hence the properties like refractive indices in the different directions are different.

This shows that the crystalline solids are anisotropic in nature.

Isotropy : The ability of amorphous solids to exhibit identical physical properties even though measured in different directions is called isotropy.
Explanation : This property arises because there is no long range order of regular pattern of arrangement in them and hence the arrangement is irregular along all the directions. Therefore the magnitude of any physical property would be identical along all directions.