Why are liquids and gases categorized as fluids?
The liquids and gases have a property to flow i.e., the molecules of liquids and gases can easily move fast and tumble over one another freely. Because of their tendency to flow, these have been categorized as fluids.
Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.
The total number of tetrahedral voids in the face centered unit cell is
(a) 6 (c) 10
(b) 8 (d) 12
‘Stability of a crystal is reflected in the magnitude of its melting points’. Comment. Collect melting points of solid water, ethyl alcohol, diethyl ether and methane from a data book. What can you say about the intermolecular forces between these molecules?
Gold (atomic radius = 0.144 nm) crystallises in a face centred unit cell. What is the length of the side of the unit cell ?
A cubic solid is made up of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body centre. What is the formula of the compound? What are the coordination numbers of P and Q?
Copper crystallises into a fee lattice with edge length 3.61 x 10-8 cm. Show that the calculated density is in agreement with its measured value of 8.92 gcm-3.
The number of tetrahedral voids per unit cell in NaCl crystal is
(c) twice the number of octahedral voids
(d) four times the number of octahedral voids
Explain how many portions of an atom located at
(i)corner and (ii)body centre of a cubic unit cell is part of its neighbouring unit cell.
Copper crystallises into a fee lattice with edge length 3.61 x 10-8 cm. Show that the calculated density is in agreement with its measured value of 8.92 gcm-3.
Why does the electrical conductivity of semiconductors increase with rise in temperature?
Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.
Solid A is a very hard electrical insulator in. solid as well as in molten state and melts at extremely high temperature. What type of solid is it?
What is the two-dimensional coordination number of a molecule in a square close-packed layer?
Explain how vacancies are introduced in an ionic solid when a cation of higher valence is added as an impurity in it.
How many lattice points are there is one unit cell of each of the following lattices?
(i) Face centred cubic (if) Face centred tetragonal (iii) Body centred cubic
What are semi-conductors? Describe the two main types of semiconductors and contrast their conduction mechanisms.
Classify each of the following as being either a p-type or n-type semiconductor :
Which of the following lattices has the highest packing efficiency (i) simple cubic (ii) body- centred cubic and (iii) hexagonal close-packed lattice?
What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?
In the cubic close packing, the unit cell has
(a) 4 tetrahedral voids each of which is shared by four adjacent unit cells
(b) 4 tetrahedral voids within the unit cell
(c) 8 tetrahedral voids each of which is shared by four adjacent unit cells
(d) 8 tetrahedral voids within the unit cells.
In which of the following arrangements octahedral voids are formed?
(a) hep (b) bcc (c) simple cubic (d) fee
In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct answer out of the following choices.
(a) Assertion and Reason both are correct statements and Reason is the correct explanation for Assertion.
(b) Assertion and Reason both are correct statements but Reason is not the correct explanation for Assertion.
(c) Assertion is correct but Reason is wrong.
(d) Assertion is wrong but Reason is correct.
Assertion (A): The total number of atoms present in a simple cubic unit cell is one.
Reason (R): Simple cubic unit cell has atoms at its comers, each of which is shared between eight adjacent unit cells.
A sample of ferrous oxide has actual formula Fe0.93 O1.00. In this sample, what fraction of metal ions are Fe2+ ions? What is the type of non-stoichiometric defect present in this sample? '
A compound is formed by two elements M and N. The element N forms ccp and atoms of the element M occupy 1/3 of the tetrahedral voids. What is the formula of the compound? (C.B.S.E. Foreign 2015)
What type of defect can arise when a solid is heated? Which physical property is affected by it and in what way?
What makes glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?
(i) What is meant by the term ‘coordination number’?
(ii) What is the coordination number of atom
(a) in a cubic close-packed structure?
(b) in a body centred cubic structure?
A cubic solid is made of two elements P and Q. Atoms Q are at the corners of the cube and P at the body centre. What is the formula of the compound ? What is the co-ordination number of P and Q?
Ferric oxide crystallises in a hexagonal dose- packed array of oxide ions with two out of every three octahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.
What is the two-dimensional coordination number of a molecule in square close-packed layer?
A compound forms hexagonal close-packed. structure. What is the total number of voids in 0. 5 mol of it? How many of these are tetrahedral voids?
Ionic solids, which have anionic vacancies due to metal excess defect, develop colour. Explain with the help of a suitable example.
Classify each of the following solids as ionic, metallic, modular, network (covalent) or amorphous:
(i) Tetra phosphorus decoxide (P4O10) (ii) Ammonium phosphate, (NH4)3P04 (iii) SiC (iv) I2 (v) P4 (vii) Graphite (viii), Brass (ix) Rb (x) LiBr (xi) Si
If the radius of the octahedral void is r and radius of the atoms in close-packing is R, derive relation between rand R.
Iodine molecules are held in the crystals lattice by
(a) London forces (b) dipole-dipole interactions
(c) covalent bonds (d) coulombic forces
In which pair most efficient packing is present?
(a) hep and bcc (b) hep and ccp
(c) bcc and ccp (d) bcc and simple cubic cell
In which of the following structure coordination number for cations and anions in the packed structure will be same?
(a) Cl– ions form fee lattice and Na+ ions occupy all octahedral voids of the unit cell.
(b) Ca2+ ions form fee lattice and F- ions occupy all the eight tetrahedral voids of the unit cell
(c) O2- ions form fee lattice and Na+ ions occupy all the eight tetrahedral voids of the unit cell
(d) S2- ions form fee lattice and Zn2+ ions go into alternate tetrahedral voids of the unit cell.
Which of the following statements are not true?
(a) Vacancy defect results in a decrease in the density of the substance
(b) Interstitial defects results in an increase in the density of the substance
(c) Impurity defect has no effect on the density of the substance
(d) Frenkel defect results in an increase in the density of the substance
Under the influence of electric field, which of the following statements are true about the movement of electrons and holes in a p-type semiconductor?
(a) Electron will move towards the positively charged plate through electron holes
(b) Holes will appear to be moving towards the negatively charged plate
(c) Both electrons and holes appear to move towards the positively charged plate
(d) Movement of electrons is not related to the movement of holes
Which of the following statements are correct?
(a) Ferrimagnetic substances lose ferrimagnetism on heating and become paramagnetic
(b) Ferrimagnetic’substances do not lose ferrimagnetism on heating and remain ferrimagnetic
(c) Antiferromagnetic substances have domain structure similar to ferromagnetic substances and their magnetic moments are not cancelled by each other
(d) In ferromagnetic substances, all the domains get oriented in the direction of magnetic field and remain as such even after removing magnetic field.
Frenkel defect is also known as
(a) stoichiometric defect (b) dislocation defect
(c) impurity defect (d) non-stoichiometric defect
