Chemistry M.C.Q (1 Marks)

Explanation: (B) n-type semiconductor.
When silicon is doped with electron rich impurity like P or As, the increase in conductivity is due to the negatively charged Electron. Hence, silicon doped with electron rich impurity is termed as 'n-type semiconductor'.

Plastic Deformation is the permanent distortion which occurs when the material is subjected to stress, tensile or compression that exceeds its yield strength.

In Face centered cubic structure octahedral voids are located at:

• Body Center
• Edge Centers

Polonium crystallises in a simple cubic structure.
Copper and Nickel crystallises in a face centred cubic structure.
Iron crystallises in a body centred cubic structure.

Amorphous solid has short range order which has a tendency to flow very slowly. Hence, it is also known as pseudo solids or super cooled liquids. Glass panes fixed to windows or doors of old buildings are invariably observed to be thicker at bottom than at the top. These are examples of amorphous solids.

Pure crystals have constituents i.e., atoms or molecules or ions as lattice points which are arranged in fixed stoichiometric ratio. Electron can occupy the lattice site only when there is imperfection in solid and not in a pure crystal.
Hence, existence of free electrons are not possible, it is possible on in case of imperfection in solid.

Wurtzite is a zinc iron sulfide mineral frequently encountered mineral form of sphalerite.

Common salt, sugar and iron are crystalline solids whereas rubber is an amorphous solid as it does not have well developed perfectly ordered crystalline structure. Other amorphous solids include tar, glass, plastic, butter etc.

a crystal, atoms are located at the position of minimum potential energy.
As two atoms approach each other, the potential energy gradually decreases, reaches a minimum value and then sharply increases.

Absorption of photons by crystal produce atomic displacement leading to imperfections.
These imperfections are also called defects.
These are deviations from perfectly ordered arrangement.

Pseudo solid is a solid which possesses the property of liquids. Glass is a pseudo solid and in a very slowprocess, it flows like a liquid due to which the base of glass gets thicker than top.

In graphite one carbon atom is attached to three other carbon atoms. One electron of carbon remains free. Due to this free valence electron graphite is an electrical conductor.

Different types of crystal system arised due to difference in the arrangement of atoms in the space.

Silver halides show both Frenkel and Schotkky defects. For Frenkel defect the reason is that there is size difference between the sizes of silver and halide.
Schottky defect is possible because silver halides are highly ionic.

Graphite is a covalent or Network solid, therefore it cannot be grouped as an ionic solid.

Glass is an amorphous solid. It is called psuedo solid. Diamond, graphite and common salt are crystalline solids.

The amorphous substance is defined as any noncrystalline solid in which the atoms and molecules are not organized in a definite lattice pattern. As Rubber, Glass and Polymers of high molecular mass are examples of amorphous solids and Copper is not an amorphous substance.
Copper is an example of a crystalline solid.

Amorphous solids are supercooled liquids and they are irregularly arranged in nature of their structure. They never possess a definite melting point.

Solids have a regular repeated molecular pattern in three dimensional space and this is due to their property of high intermolecular forces. But in liquids and gases the arrangement of molecular pattern it is irregular.

Explanation: (D) Amorphous
Crystals tend to have relatively sharp, well-defined melting points because all the component atoms, molecules, or ions are the same distance from the same number and type of neighbours; that is, the regularity of the crystalline lattice creates local environments that are the same.
Thus the intermolecular forces holding the solid together are uniform, and the same amount of thermal energy is needed to break every interaction simultaneously.
Amorphous has different property to crystal.

Amorphous solids are a type of solids that lacks definition in shape, pattern and long range order as well as do not have a well defined melting point.

A tetrahedral void in a crystal implies that the void is surrounded tetrahedrally by four spheres. The four spheres are located at the four corners of the tetrahedron.

A pure crystal consists of either atoms, molecules or ions at lattice sites. Electrons can only occupy the lattice sites when there is any vacancy at that site which means it is not a pure crystal.

The flame colours of metal ions are due to metal excess defect.
The free electrons can be excited to higher energy levels giving absorption spectra and as a consequence their compounds are coloured.

Amorphous solids do not have a regular pattern of arrangement and hence, cannot be cut with knife for a clean cleavage.

At sufficiently low temperature the thermal energy is low and the intermolecular forces bring the molecules of a substance so close that they cling to one another and occupy fixed positions. They can, however, have oscillating motion about their fixed positions. Under such condition the substance exists in solid state.

A tetrahedral site is surrounded by four spheres and hence an interstitial hole is called tetrahedral.

The solid which have fixed composition and three dimensional structure is called as crystalline solid.
Silver is a crystalline solid because it have fixed composition and structure.

In sugar, the constituent particles are arranged in a specific manner. Hence, it is a crystalline solid.
In coal, wax, and clay the constituent particles are arranged in a random manner. Hence, it is an amorphous solid.

The more efficient mode of packing of identical atoms in one layer is hexagonal close packing pattern.
This is because the empty space in hexagonal closed packing is much less than that in square close packing.

Ferromagnetic solids can be permanently magnetised and then all the domains get oriented in the direction of applied magnetic field.

Strength, photovoltaic optical properties, no sharp melting points, not bound by plane surfaces, hard etc. are the features of amorphous solids. However, they do not give diffraction bands.

In the given options, Hexagonal, Triclinic and Rhombohedral crystals have only one Bravais lattice. Only Monoclinic Crystal has two Bravais lattice.

Amorphous solids are isotropic because they show thermal and optical properties, same in all directions.

When electron rich or electron deficient impurity is added to a perfect crystal, it introduces electronic defect in them.

Glasses are amorphous solids. Amorphous solids do not have a specific arrangement pattern.
All amorphous solids have a tendency to flow though very slowly. Hence, glass is considered as a super cooled liquid. That is why, glass windows and doors become slightly thicker at the bottom than at the topwith time.
Amorphous solids do not exhibit long order arrangement.

Amorphous is defined as a substance laking clear structure or shape.
In quartz glass, elements are not organized in a periodic array, so they don't have a proper shape or structure.

Ionic bonding results in compounds which are crystalline solids.
As they are held by strong electrostatic forces, thus they have more organised structure, a definite melting point and are known as crystals.

Most crystals show good cleavage as their atoms, ions or molecule are arranged in planes which is due to flat crystal face.

Iodine molecule is a nonpolar covalent molecule. These molecules are electrically symmetical and have no dipole moment. The molecules are in a crystal lattice of iodine are, therefore, attracted together by weak 'London forces'.

The three dimensional graph of lattice points which sets the pattern for the whole lattice is called unit cell.

The smallest repeating unit in space lattice which when repeated over and again results in the crystal of the given substance is called unit cell.
The collection of all points in the crystal having similar environment is called space lattice.
The lattice points can be arranged in maximum of fourteen types. This arrangement is called Bravais lattice.
Two or more substances having the same crystal structure are said to be isomorphous.

At zero kelvin, most of the ionic crystals posses no defect. This is due to presence of highly ordered arrangement.

As temperature and number of defects are inversely propotional, with increase in temperature number of defects decreases.
In schottky effect, size of ions are almost same while in frenkel defect, size of cation is small.

In Frenkel defect, some cations occupy interstitial site and hence it is also called dislocation defect.

The structure of graphite consists of many flat layers of hexagons. The layers are called graphene sheets. Each carbon atom in the layer is joined by strong covalent bonds to only three other carbon atoms. Compare this with the structure of diamond. Each graphene sheet is itself a giant molecule.

 Since quartz glass is an amorphous solid having short range order of constitutents. Hence, value of refractive index is same in all directions, can be measured and not be equal to zero always.