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 unit cell.
A basic repeating structural unit of a crystalline solid is called a unit cell.
Define Anisotropy.
The ability of crystalline solids to change values of physical properties when measured in different directions is called anisotropy.
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
