Classification of solids of Molecular, Ionic, Metallic, and Covalent or Network solids.
Classification Of Crystalline Solids
Amorphous substances have only short-range order.
However, most solids substances are crystalline in nature.
For example, all the metallic elements (like copper, iron, and silver); non-metallic elements (like phosphorus, sulphur, and iodine), and compounds like zinc sulphide, sodium chloride, and naphthalene form crystalline solids.
Crystalline solids can be classified in various ways or methods which depends on the purpose of use.
Here, we will classify crystalline solids on the basis of the nature of intermolecular forces or bonds that hold the constituent particles(atoms, molecules, or ions) together.
These are-(1)Van der Waals forces ;(2)Ionic bonds;(3) Covalent bonds;(4) Metallic Bonds.
On the basis of crystalline solids are classified into 4 categories namely,
- Molecular solid
- Ionic solid
- Metallic solid
- Covalent solid
Table Of Content
Molecular Solids
Molecules of molecular solids are constituent particles(atom, molecule, or ions).
Types of molecular solids
1. Non-Polar Molecules Solids
2. Polar Molecules Solids
3. Hydrogen-Bonded Molecular Solids
(1)Non-polar Molecules Solids
They include either atoms, (like Argon & Helium) or the molecules formed by Non-polar covalent bonds like H₂, Cl2, and I₂ known as Non-polar molecular solids.
In these solids, the atoms or molecules are held together by weak dispersion forces or London forces.
Property of Non Polar Molecules Solid
- These solids are soft and non-conductors of electricity.
- They have low melting points.
- They are usually in a liquid or gaseous state at room temperature & pressure.
[A Non-polar covalent bond is a type of chemical bond that is formed when electrons are shared equally between two atoms. Non-polar covalent bonds are not charged]
(2) Polar Molecular Solids
The molecules of substances like HCL, SO2, etc. are formed by polar covalent bonds and are known as polar molecular solids.
The molecule in some solids is held together by relativity stronger dipole-dipole interactions.
Property of Polar Molecules Solid
- These solids are soft and non-conductors of electricity.
- Their melting point is higher than Non-polar molecular solids and most of those Non-polar molecular solids are gases or liquids under room temperature and pressure.
- An example of Polar molecular solids are solid SO2 and solid NH3
[A Polar covalent bond exists when atoms with different electronegativity share electrons in a covalent bond, for example, water HCL, SO2, and Ammonia.
Polar covalent bonds are charged(positive as well as negative). ]
(3) Hydrogen-Bonded Molecular Solids
The molecules of such solids which contain polar covalent bonds between hydrogen(H)and Fluorine(f), oxygen(O) or nitrogen(N) atoms are known as hydrogen molecular solids.
Strong hydrogen bonding binds with molecules of such a solid like H2O(Ice).
Property of Hydrogen-Bonded Molecules Solid
- They are Non-conductors of electricity.
- Generally, they are volatile liquid (quickly evaporates at room temperature)or soft solids under room temperature and pressure.
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Ionic solids
Ionic solids are made up of constituent particles (atoms, molecules, or ions) of ions. Ionic solids are formed by the three-dimensional (3D) arrangements of cation(+ve) and anion(-ve) bound or held together by strong Coulombic (electrostatic) forces.
Property of Ionic Solid
- These solids are hard and brittle in nature.
- They have high melting and boiling points.
- When iron is not free to move about, so they are electrical insulators in the solid state.
- But in the molten state or when ions of ionic solid are dissolved in water, the ions become free to move about and they conduct electricity
- For example, sodium chloride, Nickel oxide, table salt, and NaCl.
Metallic Solids
Metals are an orderly collection of positive(+ve) ions surrounded by and held together by a sea of free electrons. These electrons are mobile (movable) and electrons are evenly spread out throughout the Crystal known as metallic solids.
Each metal atom contributes one or more electrons towards this sea of mobile electrons.
Property of Metallic Solid
- These free mobile (movable) electrons are responsible for the high electrical and thermal (heat) conductivity of metals. (Thermal conductivity means when heat increases then electrons move fast easily and conduct electricity).
- When an electric field is applied, then these electrons flow through the network of positive(+ve) ions.
- Metallic solids have the property of lustre(shine) and colour due to the presence of free electrons in them.
- Metallic solids have all the properties of metals. Metals are highly malleable (beaten into a thin sheet) and ductile ( drawn into wires).
Covalent Solids|Network Solids
A wide variety of crystalline solids of non-metals result from the formation of covalent bonds between adjacent atoms( neighbouring atoms or bonds of elements) throughout the Crystal known as Giant molecules.
Covalent bonds are strong and directional( means a specific orientation or revolve around bonded atoms) in nature, therefore atoms are held very strongly at their position.
Property of Covalent Solid
- Such solids are very hard and brittle(easily break).
- They have an extremely high melting point and may even decompose before melting (due to the weak chemical bond of crystal).
- They are insulators and do not conduct electricity. for example diamond and silicon carbide.
- Exception Graphite is soft and it is a conductor of electricity due to its typical structure.
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Network Structure Of Diamond |
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Structure Of Graphite |
Carbon atoms of graphite are arranged in different layers and each carbon atom is covalently bonded to three of its neighbouring carbon atom in the same layer and the fourth valence(empty) electron of each carbon atom is present between different layers & its valence electron is free to move about.
These free electrons make graphite a good conductor of electricity.
Different layers can slide one over the other layer. This makes graphite a soft solid and a good lubricant (lubricant means a substance that helps to reduce friction between surfaces in mutual contact or bond).
Different Types Of Solids in Tabular Form
FAQ Of Classification Of Crystalline Solids
Q 1. Classify the following solids in different categories based on the nature of intermolecular
forces operating in them:
Potassium sulphate, tin, benzene, urea, ammonia, water, zinc sulphide, graphite, rubidium,
argon, silicon carbide.
Answer:
Potassium sulphate → Ionic solid
Tin → Metallic solid
Benzene → Molecular (non-polar) solid
Urea → Polar molecular solid
Ammonia → Polar molecular solid
Water → Hydrogen bonded molecular solid
Zinc sulphide → Ionic solid
Graphite → Covalent or network solid
Rubidium → Metallic solid
Argon → Non-polar molecular solid
Silicon carbide → Covalent or network solid
Q 2. 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?
Answer
The given properties are the properties of a covalent or network solid. Therefore, the given
solid is a covalent or network solid. Examples of such solids include diamond (C) and
quartz (SiO2
).
Q 3. What type of solids are electrical conductors, malleable and ductile?
Answer:
Metallic solids are electrical conductors, malleable, and ductile.
Q 4. Ionic solids conduct electricity in a molten state but not in a solid state. Explain.
Answer:
In ionic compounds, electricity is conducted by ions. In a solid state, ions are held together
by strong electrostatic forces and are not free to move about within the solid. Hence, ionic
solids do not conduct electricity in a solid state. However, in a molten state or in solution form,
the ions are free to move and can conduct electricity.
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