What is the formula of a compound in which the element Y forms CCP lattice and atoms X occupy 1 3 rd of tetrahedral voids.

Tetrahedral voids are holes or interstices surrounded by four spheres present at the corners of a tetrahedron. Suppose number of Y present in the packing = a Then, tetrahedral voids = 2 a Atoms X present in the tetrahedral voids = 1 3 × 2 a = 2 a 3 Therefore, ratio of X : Y = 2 a 3 : a = 2 3 : 1 = 2 : 3 So, the formula of compound is X 2 Y 3

A compound forms hexagonal close packed ( hcp ) structure. What is the total number of voids in 0 . 5 mol of it? How many of these are tetrahedral voids?

Number of compound units in 1 mole of close-packed structure = N A = 6.022 × 10 23 Number of compound units in 0 . 5 mole of close-packed structure = 0.5 × 6.022 × 10 23 = 3.011 × 10 23 We know that, one unit of hcp has atoms = 6 So, number of unit cells = 3 . 011 × 10 22 6 = 5 . 018 × 10 22 And if close packed structure has 6 atoms then it will have 6 octahedral voids and 12 tetrahedral voids in one unit cell. So, number of octahedral voids = 6 × 5 .018 × 10 22 = 3 . 011 × 10 23 And, number of tetrahedral voids = 12 × 5 .018 × 10 22 = 6.022 × 10 23 Therefore, total number of voids = Octahedral voids + Tetrahedral voids = 3.011 × 10 23 + 6.022 × 10 23 = 9.033 × 10 23 .

What type of solids are electrical conductors, malleable and ductile ? “Ionic solids conduct electricity in molten state but not in solid state”. Explain.

Metallic solids are electrical conductors, malleable and ductile. Ions are the constituent particles of ionic solids. Such solids are formed by the three-dimensional arrangements of cations and anions bound by strong coulombic (electrostatic) forces. These solids are hard and brittle in nature. They have high melting and boiling points. Since the ions are not free to move about, they are electrical insulators in the solid-state. However, in the molten state or when dissolved in water, the ions become free to move about, and they conduct electricity.

Define semiconductor. Classify each of the following as being either a p-type or an n-type semiconductor : B doped with Si.

Semiconductors: These are the solids with conductivities in the intermediate range from 10 - 6 to 10 4 ohm - 1 m - 1 . p-type semiconductor: The number of holes is very large as compared to the number of electrons. Thus, the holes are the major charge carrier and the electrons are the minor charge carriers for the p-type semiconductor. So, when silicon is doped with boron, the three electrons of boron bond with the three electrons of silicon. The bond between the electrons is the covalent bond. Hence, the doping silicon with boron produces a p-type semiconductor.

Define semiconductor. Classify each of the following as being either a p-type or an n-type semiconductor : Ge doped with In.

Semiconductors: These are the solids with conductivities in the intermediate range from 10 - 6 to 10 4 ohm - 1 m - 1 . Silicon or germanium can also be doped with a group of 13 elements like B, Al or Ga which contains only three valence electrons. The place where the fourth valence electron is missing is called electron-hole or electron vacancy. These types of semiconductors are called p-type semiconductors.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - The Solid State>Assam Board-2019>Q 9

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12th Assam Board

IMPORTANT

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Calculate the packing efficiency of a metal crystal for a simple cubic lattice.

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