Tag: chemistry

Questions Related to chemistry

The thermal conductivity of silver and copper is high because they have following binding :

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Metallic

  2. Ionic

  3. Covalent

  4. Vander Waal

Show answer
Correct Option: A
Explanation:

The thermal conductivity of silver and copper is high because they have metallic bonding.


Silver and copper are metals. They form metallic bonds. They contain mobile electrons immersed in a sea of positively charged metal cations. 

These mobile electrons can move from one end of metal to other end. Hence, they conduct electricity.

Therefore, option A is correct.

The molecular range for materials is :

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. $10^{-12}m$

  2. $10^{-10}m$

  3. $10^{-11}m$

  4. $10^{-9}m$

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Correct Option: D
Explanation:

The molecular range for materials is $10^{-9}m$. It can also be expressed in terms of nanometers. $1  nm =10^{-9}m$. 

Metallic bonding is explained by :

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. band model

  2. electron-sea model

  3. both (a) and (b)

  4. None of these

Show answer
Correct Option: C
Explanation:

Both theories have their own arguments to explain metallic bonding.
Each metal atom allows its electrons to roam freely, so these atoms become positively charged cations. These cations are kind of like a positively charged island and are surrounded by a sea of negatively charged electrons.

Some of the following properties are important in determining whether an element has metallic properties.
I : atomic number
II : atomic weight
III: number of valence electrons
IV: number of vacant atomic orbitals
V: total number of electronic shells in the atom
Select correct properties from the codes given below:

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. I, II, III, IV

  2. I, III, IV, V

  3. III, IV

  4. III, IV, V

Show answer
Correct Option: C
Explanation:

The following properties are important in determining whether an element has metallic properties.
III: number of valence electrons
IV: number of vacant atomic orbitals
All metals are electropositve elements and have a tendency to lose electrons.  Alkali metals and alkaline earth metals contain one and two valence electrons respectively.They readily lose these electrons and show metallic properties. Transition metals have a number of vacant d orbitals and show variable valency. Due to the presence of vacant d orbitals, they show variable valence.

A solid melt slightly above $273K$ and is a poor conductivity of heat and electricity. To which of the following categories does it belong?

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Ionic solid

  2. Covalent solid

  3. Metallic solid

  4. Molecular solid

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Correct Option: D

Which of the following is an example of molecular solid?

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Zinc Sulphide

  2. Magnesium Oxide

  3. Dry ice

  4. Diamond

Show answer
Correct Option: C
Explanation:

Molecular solids refer to those solids which are composed of molecules held together by the van der Waals forces. 

Examples are hydrogen, carbon dioxide etc.

ZnS is a crystalline solid.
MgO is an ionic solid.
Diamond has a network structure.

Hence, dry ice $(CO _2)$ is an example of a molecular solid.

A solid melts slightly above $273$ K and is a poor conductor of heat and electricity. To which of the following categories does it belong?

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Ionic

  2. Covalent

  3. Metallic

  4. Molecular

Show answer
Correct Option: D
Explanation:

Metals are good conductors of heat and electricity with variable melting points.
Ionic solids are also good conductors of heat and electricity with very high melting points.
Covalent solids are non conductor of electricity and heat with very high melting points due to their strong bonding.
Molecular solids are poor conductors of heat and electricity and they have lower melting point than ionic solids.

Molecular crystals exists in:

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. crystalline state

  2. amorphous state

  3. non-crystalline state

  4. None of the above

Show answer
Correct Option: A,B,C
Explanation:

Molecular crystals exist in all crystalline state, an amorphous state, and non-crystalline state. Molecular crystals are substances that have relatively weak intermolecular binding, such as dry ice (solidified carbon dioxide), solid forms of the rare gases (e.g., argon, krypton, and xenon).

What state are most ionic compounds at room temperature?

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. Solid

  2. Liquid

  3. Gas

  4. Plasma

Show answer
Correct Option: A
Explanation:

Generally, ionic compounds exist in solid state due to strong electrostatic ionic forces present between the molecules of solids.


For example;  NaCl or KCl 

Hence, option $A$ is correct.

Metallic solids are always opaque because:

chemistry solid state classification of crystalline solids classification of solids introduction to solids

  1. they reflect all the incident light

  2. they scatter all the incident light

  3. the incident light is readily absorbed by the free electrons in a metal

  4. the energy band traps the incident

Show answer
Correct Option: C
Explanation:

Metals are opaque because they have metallic bonding which means that all of the atoms are surrounded by free-moving electrons.


The incident light on metals is absorbed by large numbers of available free electrons in metals to increase their kinetic energy and hence they are opaque.