Chemistry 1 Marks Question

Presence of F-centres.

Their conductivity is increased by adding an appropriate amount of suitable impurity/by doping.

Dipole–Dipole interaction.

Metallic solid conducts electricity in solid state but ionic solids do so only in molten state or in solution or metals conduct electricity through electrons and ionic substances through ions.

4.

4.

Because of some crystallisation.

Ferromagnetism.

4.

Addition of a suitable impurity to the semi-conductor to increase its conductivity is called Doping.

It means that some of their physical properties show different values when measured along different directions in the same crystal.

Mode of conduction, through electrons in solid metal and through ions in molten state or in solution in ionic solid/Metals are malleable and ductile whereas ionic solids are hard and brittle.

Frenkel defect.

2

XY.

By melting the material and then cooling it rapidly.

The intermolecular forces of attraction that are present in solids are very strong. The constituent particles of solids cannot move from their positions i.e., they have fixed positions. However, they can oscillate about their mean positions. This is the reason solids are rigid.

The empty spaces present between the atoms or the ions when they are packed within the crystal are called voids.

On heating, amorphous substance change to crystalline form at some temperature. This is due to crystallization.

1. ZnS shows Frenkel defect.
2. AgBr shows Frenkel as well as Schottky defect.

1. Stoichiometric defects, viz., Schottky defect and Frenkel defect.
2. Non-stoichiometric defects, viz., metal excess, metal deficiency,
3. Impurity defects.

Metallic solids are electrical conductors, malleable and ductile.

The significance of a lattice point is that each lattice point represents one constituent particle of a solid which may be an atom, a molecule (group of atom), or an ion.

Six.

If, as a result of the imperfections in the crystal, the ratio of the cations to the anions becomes different from that indicated by the ideal chemical formula, then the defects are termed as non-stoichiometric defects.

Silicon doped with phosphorus gives n-type whereas silicon doped with gallium are p-type semiconductors.

Electrical conductivity decreases with rise in temperature because kernels begin to vibrate and create hindrance in the flow of electrons.

Metal excess defect due to anionic vacancies.

Primitive unit cells have one atom per unit cell. On the other hand, non-primitive unit cells have more than one atom per unit cell.

There are 9 (1 from the centre + 8 from the corners) lattice points in body-centred cubic.

p-type semiconductor.

There are 14 (8 from the corners + 6 from the faces) lattice points in face-centred tetragonal.

When a solid is heated, vacancy defect can arise. A solid crystal is said to have vacancy defect when some of the lattice sites are vacant.
Vacancy defect leads to a decrease in the density of the solid.

The property of a substance to offer no resistance to the flow of electricity at a particular temperature is known as superconductivity.

Explanation:

In antiferromagnetic substances their domains (a group of small regions of metal ions) are oppositely oriented and cancel out each other’s magnetic moments [as depicted in Figure (iv)] above.

Anisotropy: Crystalline solids are anisotropic in nature, that is some of their physical properties like electrical resistance or refractive index show different values when measured along different directions in the same crystal. This arises from different arrangement of particles in different directions arrangement of particles along different directions.

Isotropy: In case of amorphous substances, properties such as electrical conductivity, refractive index, thermal expansion, etc. are identical in all directions just as in case of gases or liquids. This property is called isotropy and the substances showing this property are called isotropic.

When some ions (usually cations) are missing from the lattice sites and they occupy the interstitial sites so that electrical neutrality as well as stoichiometry is maintained, it is called Frenkel defect.

Atoms or ions that fill the normal vacant interstitial voids in a crystal are called interstitials.

Packing efficiency of:

1. Simple cubic = 52.4%
2. Body-centred cubic = 68%
3. Hexagonal close-packed = 74%

Hcp lattice has the highest packing efficiency.

Impurity from group 15 should be added to get n-type semiconductor.

The free electrons trapped in the anion vacancies are called F-centres.

Dispersion forces, dipole–dipole interactions and hydrogen bonds.

Silicon doped with Al forms p-type semiconductors, while silicon doped with P produces n-type semiconductors.

In 2D, square close-packed layer, an atom touches 4 nearest neighbouring atoms. Hence, its CN=4.

In solid state, the ions cannot move, they are held by strong electrostatic forces of attraction. So, ionic solids do not conduct electricity in solid state. However, in the molten state, they dissociate to give tree ions and hence conduct electricity.

Similar to liquids, glass has a tendency to flow, though very slowly. Therefore, glass is considered as a super cooled liquid. This is the reason that glass windows and doors are slightly thicker at the bottom than at the top.

Electrical conductivity of semiconductors increases with increase in temperature as more electrons can jump from valence band to conduction band.

Coordination no. of A = 8, Coordination no. of B = 4.

A face-centred cubic structure has one atom at each corner and one atom at each face centre.

p-type semiconductor.

There are 14 (8 from the corners + 6 from the faces) lattice points in face-centred cubic.

n-type of semiconductor is obtained.

When some ions (usually cations) are missing from the lattice sites and they occupy the interstitial sites so that electrical neutrality as well as stoichiometry is maintained, it is called Frenkel defect.

Ferromagnetism.

The constituent particles of a solid have fixed positions and are not free to move about, i.e., they possess rigidity. That is why they have definite volume.

Glass is not a true solid but a supercooled liquid of high viscosity (called pseudo-solid). It has the property to flow.

Because of the Frenkel defect, no ion is missing from the crystal, therefore there is no change in density.

Explanation:
n-type semiconductors are prepared by doping perfect crystal of silicon (Si) with pentavalent elements of group 15 (viz. P and As). Some of the lattice sites in silicon crystal are occupied by fifth electron which is left over as extra electron and couldn't form a bond with tetravalent Si. The images (i) and (iii) exhibits this situation representing n-type semiconductor.

Impurity defect.

Imperfection refers to the irregularities in the arrangement of atoms, ions or molecules in the structure of crystalline substances.