Constituent particles in ionic solids of the Crystalline Solids are anions (negatively charged) and cations (positively charged). An ion is surrounded by a typical number of opposite charges. For example, in NaCl, the Na+ ion is surrounded by 6 Cl- ions. Ions in these solids are held together by strong electrostatic forces. They have high melting and boiling points and are soluble in polar solvents but not in non-polar solvents.

CLASSIFICATION OF CRYSTALLINE SOLIDS:-

Based upon nature of constituent particles and binding forces present in them:-

1. Ionic Solids:- 

• In these solids constituent particles are positive and negative ions. (cation or anions). They are held together by strong columbic electrostatic forces of attraction examples are NaCl, CaCl2, MgCl2, BaCl2 etc.

Characteristics of ionic solids:-

1. They have high melting and boiling points
2. They are soluble in polar solvents but are insoluble in non polar solvents.
3. Due to strong electrostatic forces of attraction they are closely packed hence hard but they are brittle.

2. Molecular Solids:-

• In these solids the constituent particles are molecules on the nature of molecules they can further subdivided into following three types:-

1. Non polar molecular solids:-

• • The crystalline solids in which constituent particles are atoms of noble gases [helium, neon] or non polar molecules like [H2, Cl2, I2]

Their characters are:-

1. 1. They are soft due to weak intermolecular forces.
   2. They are non conductors of electricity. They have low melting and boiling points.

2. Polar molecular solids:-

• • The crystalline solids in which constituent particles are polar molecules like HCl, SO2 etc. the intermolecular forces of attraction are dipole – dipole forces of attraction.

Thus their characters are:-

1. 1. They are soft; they are non conductors of electricity.
   2. Their melting and boiling points are high then non polar solids. They exists gases or liquid at room temperature.

3. Hydrogen bonded – molecular solids:-

• • In these solids the constituent particles are which contain hydrogen atom linked to high electronegative atoms as N, O, F

Their characters are:-

1. 1. They exists as volatile liquids or gases at room temperature.
   2. They are non conductor of electricity.
   3. Their melting and boiling points are high.

3. Covalent or network solids:-

• In these crystalline solids the constituent particles are non metal atoms linked to adjacent atom by covalent bond throughout the crystal. They forms a network of covalent bonds and exists as giant molecules. Example: Diamond

Their main characteristics are:-

1. As covalent bond is strong and directional in nature, these solid are very hard and brittle.
2. They have extremely high melting points and decompose before melting.
3. They are insult of and do not conduct electricity one exception is graphite which is covalent solid but is soft and also a good conductor of electricity.

4. Metallic solids:-

• In natural the constituent particles are positively charged metal ions – and free electrons.
• They are formed of metal atoms which lose their valance electrons to left behind positively charged ions.
• These metal atoms are surrounded by the sea of electrons each metal atom contributes one or more electrons to this sea of electrons.
• The electrons are simultaneously attracted by the +ve ions and holds these +ve ions ether

Metallic bond:-

• The force that holds the metal ion together in the crystal is called metallic bond.

Properties of metallic solids:-

1. They possess high electrical and thermal conductivity.
2. They possess lusture and colour in some case due to presence of sea of free electrons.
3. They are highly malleable and ductile.
4. They are closely packed. They exhibit high melting points and high densities.

Most of the solids found in daily life and practice are crystalline in nature. For Example metals like silver, copper, and iron, non-metals like iodine, sulphur and iodine and several compounds like NaCl (Sodium Chloride/Common Salt) etc. fall into the category of crystalline solids. We know that attraction nature of constituent particle is mainly responsible for the existence of solids. On the basis of nature of force operating between constituent particles of matter, crystalline solids are classified into four categories, namely:

• Molecular Solids

• Ionic Solids

• Metallic Solids

• Network or Covalent Solids

Amorphous silicon is a photovoltaic material widely used for conversion of sunlight into electricity.
The glass used in making glassware, rubber used in making hot water bags and cotton candy are amorphous solids

Pseudo-solid- are solids which are considered to be solid though they resembles in many respects liquid. They flow very slowly at room temperature and are considered as super cooled liquids. Amorphous solids are considered to be pseudo solid for e.g. Glass.
 

Amorphous Solids

The solids in which the constituent particles of matter are arranged in a random manner are called amorphous solids. It is a non-crystalline solid with no proper arrangement of atoms in the solid lattice. In other words, we can define amorphous solids as materials which don’t have certain organized arrangement of atoms and molecules. Most solids are amorphous in nature and are utilized in many sectors as well. One of the most common examples of amorphous solids is glass, which is used widely in the manufacturing sector.

Crystalline Solids

The solids in which the constituent particles of matter are arranged and organized in a specific manner are called Crystalline Solids. These solids contain crystals in their structure and each crystal has definite geometry. Adding further, as crystalline solids have low potential energy, they are the most stable form of solids. Almost all solids fall in the category of crystalline solids including metallic elements (iron, silver, and copper) and non-metallic elements (Phosphorus, Sulphur, and iodine). Also several compounds like sodium chloride, zinc sulphide and naphthalene build crystalline solids.

HRD Minister Ramesh Nishank announced a major CBSE syllabus reduction for the new academic year 2020-21 on July 7 which was soon followed by an official notification by CBSE on the same.

Considering the loss of classroom teaching time due to the Covid-19 pandemic and lockdown, CBSE reduced the syllabus of classes 9 to 12 with the help of suggestions from NCERT.

The CBSE syllabus has been rationalized keeping intact the learning outcomes so that the core concepts of students can be retained.

Click on the given link:

<a data-toggle="collapse" href="http://cbseacademic.nic.in/Revisedcurriculum_2021.html#collapse12">Revised Languages - (Group-L)</a>

<a data-toggle="collapse" href="http://cbseacademic.nic.in/Revisedcurriculum_2021.html#collapse13">Revised Academic Electives - (Group-A)</a>

<a data-toggle="collapse" href="http://cbseacademic.nic.in/Revisedcurriculum_2021.html#collapse14">Co-Scholastic Areas</a>

<a data-toggle="collapse" href="http://cbseacademic.nic.in/Revisedcurriculum_2021.html#collapse15">Curriculum Deduction Details (Deleted Portion only for the purpose of Annual Examination-2021) This has to be read along with the revised syllabus and also with the Alternative Calendar of NCERT</a>

a n s w e r
 Classification of Crystalline Solids
Ionic Solids:- ...
Molecular Solids:- ...
Non polar molecular solids:- ...
Polar molecular solids:- ...
Hydrogen bonded – molecular solids:- ...
Covalent or network solids:- ...
Metallic solids:-

Thermal Energy

• Thermal energy refers to the energy of a body that arisesfrom the motion of its atoms or molecules.
• The thermal energy of a substance is directly proportional to the temperature of the substance.
• It is also defined as the measure of average kineticenergy of the constituent particles of a substance and hence responsible for movement of those particles.

Characteristics of solid state

• They have definite shape due to strong Intermolecular forces of attraction.
• They have distinct boundaries.
• They have a fixed volume.
• They cannot flow.
• They have negligible compressibility due to negligible distance between the neighbouring molecules.
• They possess a tendency to uphold their shape when exposed to external force.
• They break under force but it is difficult to change their shape so they are rigid.

Solids are rigid, because of the relative stronger intermolecular attractions between them as compared to solids and liquids. Those all forces are electrostatic in nature. By supplying heat the increased kinetic energy of the molecules by which we can change the shape or volume of the substance.

Protection of Colloids

Lyophobic sols such as those of metals like gold, silver etc. can be easily precipitated by the addition of a small amount of electrolytes.

They can be prevented from coagulation by the previous addition of some stable lyophilic colloids like gelatin, albumin, etc. This is because when a lyophilic sol is added to the lyophobic sol, the lyophilic particles form a layer around the lyophobic particles and this protect them from electrolytes.

If a small amount of gelatin is added to gold sol, it is not readily precipitated by the addition of sodium chloride. This process of protecting the lyophobic colloidal solutions from precipitation by the electrolytes due to the previous addition of some lyophilic colloid is called protection. The colloid which is added to prevent coagulation of the colloidal sol is called protecting colloid.

Dehydration reaction is a type of chemical reaction wherein water is formed from the extraction of the components of water from a single reactant. An alkene is produced when dehydration of an alcohol is performed. A basic structural equation for alcohol dehydration is as follows:

C₂H5₅OH → C₂H₄ + H₂O.

Basically, it is a measure of how much the solvent molecules tend to escape from a liquid or solid phase into the atmosphere. Vapor pressure of a liquid is a colligative property.

Electrophoresis and electro-osmosis

• In electrophoresis, solid particles (macromolecule like nucleic acids or protein) is moved using an electric field. But in electro-osmosis, a liquid is moving.
• In electrophoresis, the support solid material is a gel. But in electro-osmosis, it can be a gel, membrane, capillary, etc.

Tyndall effect:- Tyndall effect is a scattering of light when a light beam is passed through a colloidal.

Example;- Shining a flashlight beam into a glass of milk is an excellent demonstration of Tyndall effect.

Colligative properties are properties of a solution which depend only on the number of particles like ions or molecules of the solute in a definite amount of the solvent but not on the nature of the solute.

Lyophilic & Lyophobic Colloids:

Lyophilic colloids can be prepared by just heating the solid with the liquid dispersion medium.

Whereas the lyophobic colloids cannot be prepared just by heating, they need to be prepared by some special methods.

The two methods by which the lyophobic colloids can be prepared are as follows:

1. Dispersion method

2. Aggregation method

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