Schools across state won’t reopen before Diwali: Maharashtra Govt. Mumbai: With Covid-19 positive cases showing no signs of slowing down in Maharashtra, the state government has decided to allow schools to reopen only after Diwali. This means children in over 1.2 lakh schools won’t be able to attend classes in person till November. Minister of School Education Varsha Gaikwad said the decision was taken after a meeting between her department and several school managements. Since schools are not ready to risk the lives of their students, the state has planned to push the reopening after Diwali, she said. Gaikwad said the Centre had sought the state government’s views about the resuming classes in schools for senior students. She said the Centre had also issued standard operating procedures or SOPs for the partial resumption of teaching activities in schools for students of Classes 9 to 12, on a voluntary basis, from September 21. Advertisement Advertisement “However, school managem...
Solid state
Exercise part 2.
Q no 2) Answer the following in one or two sentences
(i) What are the types of particles in each of the four main classes of crystalline solids ?
Answer : Types of the particles in each four main classes of crystalline solid are : –
- Ionic Crystals
- Covalent Network Crystals
- Molecular Solids
- Metallics Crystals
(ii) Which of the three types of packing used by metals makes the most efficient use of space and which makes the least efficient use ?
Answer :
Close packing efficiency is maximum in the crystal lattice of Face Centered cubic (FCC) unit cell and it is minimum in the crystal lattice of Simple Cubic unit cell.
- In the crystal lattice of Face Centered cubic (FCC) unit cell the packing efficiency is 74 %.
- In the crystal lattice of Simple Cubic unit cell, the packing efficiency is 52.4%.
(iii) The following pictures show population of bands for materials having different electrical properties. Classify them as insulator, semi conductor or a metal.
![](data:image/svg+xml;charset=utf-8,<svg height="123px" width="182px" xmlns="http://www.w3.org/2000/svg" version="1.1"/>)
Answer : In the Given Figure ,
![](data:image/svg+xml;charset=utf-8,<svg height="576px" width="1024px" xmlns="http://www.w3.org/2000/svg" version="1.1"/>)
Figure (i) Metal Conductor
FIgure (ii) Insulator
FIgure (iii) Semi Conductor
iv) What is the Unit Cell ?
Answer : Unit Cell is defined as the smallest repeating structural unit of a crystalline solid.
v) How does electrical conductivity of a semiconductor change with temperature ? Why ?
Answer : As the temperature increases, the electrical conductivity of the semiconductor also increases.
Reason : With Increase in temperature more electrons get the energy to jump from Conduction band to valence band, and thereby increases the conductivity of the semiconductor.
vi. The picture represents bands of MOs for Si. Label valence band , conduction band and band gap.
![](data:image/svg+xml;charset=utf-8,<svg height="168px" width="180px" xmlns="http://www.w3.org/2000/svg" version="1.1"/>)
12th Chemistry Solid State
Answer :
vii. A solid is hard, brittle and electrically non conductor. Its melt conducts electricity. What type of solid is it ?
Answer : It is Ionic Solid.
viii. Mention two properties that are common to both hcp and ccp lattices.
Answer : The Common properties of hcp and ccp lattices are : –
- A CCP arrangement has a total of 4 spheres per unit cell and an HCP arrangement has 8 spheres per unit cell. However, both configurations have a coordination number of 12
- Number of Octahedral Voids is Same in Both the Lattices.
ix. Sketch a tetrahedral void.
Answer :
x. What are ferromagnetic substances ?
Answer : The substances containing large number of unpaired electrons are strongly attracted by magnetic field. These substances are said to be ferromagnetic.
Thank you.
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