Definitions [7]
A solid is defined as the form of matter, which possesses rigidity, have a definite volume, mass and shape. These characteristics are due to the existence of strong forces of attraction among the constituent particles of the solid.
Define Anisotropy.
The ability of crystalline solids to change values of physical properties when measured in different directions is called anisotropy.
Define unit cell.
A basic repeating structural unit of a crystalline solid is called a unit cell.
A pure semiconductor with very low but finite electrical conductivity is called an intrinsic semiconductor.
The process by which impurities are introduced into semiconductors to enhance their conductivity is called doping.
A doped semiconductor, having higher conductivity than a pure intrinsic semiconductor, is an extrinsic semiconductor.
Define the following term:
Ferromagnetism
Ferromagnetism is defined as the phenomenon in which substances, such as iron, cobalt and nickel, are strongly attracted by a magnetic field. Such substances are called ferromagnetic substances.
Theorems and Laws [1]
Name the law or principle to which the following observations confirm:
When 9650 coulombs of electricity is passed through a solution of copper sulphate, 3.175 g of copper is deposited on the cathode (at. wt. of Cu = 63.5).
Faraday’s first law of electrolysis: The mass of a substance deposited or liberated at an electrode is directly proportional to the quantity of electricity passed through the electrolyte.
Given: Charge passed = 9650 C
Atomic mass of Cu = 63.5
Valency of Cu in CuSO4 = 2
Equivalent mass of Cu = `63.5/2` = 31.75
Now, Mass deposited = `9650/96500 xx 31.75`
= 0.1 × 31.75
= 3.175 g
Key Points
| Property | Ionic Solids | Covalent Network Solids | Molecular Solids | Metallic Solids |
|---|---|---|---|---|
| Particles | Cations and anions | Covalently bonded atoms | Mono/polyatomic molecules | Metal ions in a sea of electrons |
| Forces | Electrostatic | Covalent bonds | London, dipole-dipole, H-bonding | Metallic bonds |
| Hardness | Hard and brittle | Very hard | Soft | Soft to very hard |
| Melting point | 600–3000°C | 1200–4000°C | Low (−272 to 400°C) | −39 to 3400°C |
| Conductivity | Poor (solid); good (molten/aqueous) | Poor (except graphite; diamond conducts heat) | Poor | Good conductor of heat and electricity |
| Examples | NaCl, CaF₂ | Diamond, silica | Ice, benzoic acid | Na, Mg, Cu, Au |
Solids are classified into three groups based on conductivity:
| Type | Conductivity (Ohm⁻¹ m⁻¹) | Band Gap | Reason | Examples |
|---|---|---|---|---|
| Metallic conductors | 10⁴ – 10⁷ (very high) | No band gap (overlapping s & p bands) | Motion of electrons | Cu, Al, Ag |
| Insulators | 10⁻²⁰ – 10⁻¹⁰ (very low) | Large (forbidden zone) | Electrons cannot cross | Diamond, wood, rubber |
| Semiconductors | 10⁻⁶ – 10⁴ (moderate) | Small | Motion of interstitial electrons/holes | Si, Ge |
Conductivity of metals decreases with increase in temperature; conductivity of semiconductors increases with temperature.
Motion of electrons generates a magnetic field — each electron behaves like a tiny bar magnet with a magnetic moment measured in Bohr Magneton (μ_B) = 9.27 × 10⁻²⁴ A m².
| Type | Nature | Electron Configuration | Examples |
|---|---|---|---|
| Diamagnetic | Weakly repelled by magnetic field; magnetised in opposite direction | All electrons paired | NaCl, H₂O, N₂, C₆H₆, F₂, benzene |
| Paramagnetic | Weakly attracted by magnetic field; magnetised in same direction | Unpaired electrons; lose magnetism when field removed | O₂, Cu²⁺, Fe³⁺, Cr³⁺ |
| Ferromagnetic | Strongly attracted; can be permanently magnetised (all domains align in field direction) | Unpaired electrons + aligned domains | Fe, Co, Ni, Gd, CrO₂ |
Important Questions [6]
- Name the law or principle to which the following observations confirm: When 9650 coulombs of electricity is passed through a solution of copper sulphate, 3.175 g of copper is deposited on the cathode
- The Complexion Ni(Cn)42- Is:
- Explain Why: (I) Transition Elements Form Coloured Compounds. (Ii) Interhalogen Compounds Are More Reactive than Their Constituent Elements. (Iii) Cu+ Is Diamagnetic but Cu2+ Is Paramagnetic. (Z = 29)
- Which one of the following compounds is diamagnetic and colourless?
- Give a reason for the following: Cu+2 salts are paramagnetic, while Cu+ salts are diamagnetic.
- The metal complex ion that is paramagnetic is ______. (Atomic number of Fe = 26, Cu = 29, Co = 27 and Ni = 28)
Concepts [29]
- Introduction to Solid State
- Classification of Solids
- Classification of Crystalline Solids
- Space Lattice
- Definition of Unit Cell
- Different Types of Cubic Systems
- Number of Particles Per Unit Cell in Different Cubic Systems
- Calculation of the Space Occupied (Packing Fraction) in the Unit Cells of Different Types of Cubic Systems
- Calculation of Density of a Crystal
- Close-packed Structures
- Packing of Constituent Particles in Crystals
- Voids in Close-Packed Structures
- Dimensions of Voids
- Location of Tetrahedral Voids
- Location of Octahedral Voids
- Radius Ratio Rules
- Number of Voids Filled and the Formula of the Compound
- Types of Crystalline Solids: Molecular Solids
- Types of Crystalline Solids: Ionic Solids
- Types of Crystalline Solids: Covalent Solids {Atomic or Network Solids)
- Types of Crystalline Solids: Metallic Solids
- Imperfections (Defects) in Solids
- Imperfections (Defects) in Solids: Electronic Imperfections
- Imperfections (Defects) in Solids: Atomic Imperfections
- Imperfections (Defects) Caused by Impurities
- Properties of Solids: Electrical Properties
- Properties of Solids: Magnetic Properties
- Properties of Solids: Dielectric Properties
- Amorphous Solids
