Grade 12
  1. Solid state  1.1. Classification of solids  1.2. Crystal Lattice and Unit Cell  1.3. Packing Efficiency  1.4. Density of unit cell  1.5. Imperfections in solids (point and line defects)  1.6. Electrical Properties of Solids (Conductors, Insulators and Semiconductors)  1.7. Magnetic Properties of Solids (Diamagnetic, Paramagnetic and Ferromagnetic Materials)
  2. Solution  2.1. Types of Solutions (Homogeneous and Heterogeneous)  2.2. Expressing concentration of solutions (mass %, volume %, molarity, molality, normality, mole fraction)  2.3. Solubility of solids and gases in liquids (Henry's law)  2.4. Raoult's Law and Ideal and Non-Ideal Solutions  2.5. Syndrome properties  2.6. Abnormal molar mass and Van't Hoff factor
  3. Electrochemistry  3.1. Electrochemical cells (galvanic and electrolytic cells)  3.2. Galvanic cell and EMF of the cell  3.3. Standard electrode potential and electrochemical series  3.4. Nernst equation and its applications  3.5. Conductivity and electrolytic cells (specific, molar and equivalent conductivity)  3.6. Kohlrausch's law and its applications  3.7. Batteries (primary and secondary cells)  3.8. Corrosion and its prevention
  4. Chemical kinetics  4.1. Rate of chemical reaction  4.2. Factors affecting the reaction rate (concentration, temperature, catalyst, surface area)  4.3. Order and molecularity of the reaction  4.4. Integrated Rate Equations (Zero, First and Second Order)  4.5. Half-life of a reaction  4.6. Collision theory and activation energy  4.7. Arrhenius equation and its applications
  5. Surface chemistry  5.1. Adsorption and its types (Physicosorption and Chemisorption)  5.2. Catalysis and its types (homogeneous and heterogeneous)  5.3. Colloids and their properties (Tyndall effect, Brownian motion, coagulation)  5.4. Emulsions and gels  5.5. Applications of Colloids
  6. General principles and processes of separation of elements  6.1. Presence of metals and minerals  6.2. Concentration of ores (gravity separation, froth flotation, magnetic separation)  6.3. Extraction of raw metals (roasting, calcination, reduction)  6.4. Thermodynamic and electrochemical principles of metallurgy  6.5. Refining of metals
  7. P-block elements  7.1. Group 15 elements (nitrogen and phosphorus)  7.2. Group 16 Elements (Oxygen, Sulphur and their Compounds)  7.3. Group 17 Elements (Halogens and their Compounds)  7.4. Group 18 Elements  7.5. Properties and Trends in p-Block Elements  7.6. Important compounds of p-block elements (ammonia, phosphine, sulphuric acid, hydrochloric acid)  7.7. Interhalogen compounds and their applications
  8. d-block and f-block elements  8.1. General Properties of Transition Metals  8.2. Properties of Inner Transition Metals (Lanthanoids and Actinoids)  8.3. Lanthanoid and actinoid contractions  8.4. Coordination Chemistry of d-Block Elements
  9. Coordination compounds  9.1. Werner's theory and modern concepts  9.2. Coordination number and type of ligand  9.3. Nomenclature of Coordination Compounds  9.4. Isomerism (geometrical and optical) in coordination compounds  9.5. Bonding in Coordination Compounds (Valence Bond Theory and Crystal Field Theory)  9.6. Stability and applications of coordination compounds in medicine and industry
  10. Haloalkanes and haloarenes  10.1. Classification and nomenclature of haloalkanes and haloarenes  10.2. Physical and Chemical Properties of Haloalkanes and Haloarenes  10.3. Mechanism of Nucleophilic Substitution Reactions (SN1 and SN2)  10.4. Uses and environmental effects (ozone depletion, CFCs)
  11. Alcohol, phenol and ether  11.1. Structure and classification of alcohols, phenols and ethers  11.2. Preparation and properties of alcohols  11.3. Preparation and properties of phenol  11.4. Preparation and properties of ethers  11.5. Chemical Reactions and Uses
  12. Aldehydes, ketones and carboxylic acids  12.1. Structure and nomenclature in aldehydes, ketones and carboxylic acids  12.2. Preparation and properties of aldehydes and ketones  12.3. Chemical reactions in aldehydes, ketones and carboxylic acids (nucleophilic addition, oxidation and reduction)  12.4. Preparation and Properties of Carboxylic Acids  12.5. Chemical Reactions and Uses of Carboxylic Acids
  13. Nitrogen-containing organic compounds  13.1. Amines (classification, structure, basicity)  13.2. Preparation and properties of amines  13.3. Reactions of Amines (Diazotization, Carbylamine Reaction)  13.4. Diazonium salts and their applications in paint industry
  14.1. Carbohydrates (classification and properties)  14.2. Proteins (Structure and Function)  14.3. Enzymes (Mechanism and Function)  14.4. Nucleic acids (DNA and RNA)  14.5. Vitamins and hormones
  15. Polymer  15.1. Classification of Polymers (Addition, Condensation, Copolymers)  15.2. Types of polymerization (free radical, ionic, condensation)  15.3. Important Polymers and Their Uses  15.4. Biodegradable and non-biodegradable polymers
  16. Chemistry in Everyday Life  16.1. Drugs and their classification (analgesics, antipyretics, antibiotics, antacids)  16.2. Chemicals in food and cosmetics (preservatives, artificial sweeteners, antioxidants)  16.3. Cleaning agents and detergents (soaps, synthetic detergents, surfactants)  16.4. Environmental Chemistry (Pollution, Green Chemistry, Sustainable Chemistry)

Grade 12 → Solid state ↓


Crystal Lattice and Unit Cell


In the field of solid state chemistry, it is important to understand the structure of solids. A very fundamental concept in explaining this structure of solids involves the ideas of the crystal lattice and the unit cell. These concepts provide a systematic method for describing the ordered and three-dimensional arrangement of atoms or molecules within a crystalline solid. This discussion goes into great detail about these two important structures.

What is a crystal lattice?

A crystal lattice is an orderly and periodic arrangement of atoms or molecules in a solid. It extends in all directions and forms a repetitive pattern. Imagine a city viewed from a high place: the streets, buildings and squares are arranged in a regular and repetitive pattern. Similarly, in a crystal, the atoms are arranged in a regular and repetitive manner.

A crystal lattice can be thought of as an infinite array of points in space, where each point has a similar environment to its neighbors. This symmetry and repeatability defines the unique characteristics of crystalline materials.

    
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    </svg>

Characteristics of crystal lattices

Each point in a crystal lattice is called a lattice point, and it can be an atom, molecule, or ion. The entire structure of a crystal is made up of countless such lattice points. Given the repetitive nature, these properties of regularity and periodicity are important:

  • Symmetry: Crystal lattices exhibit symmetry, where some of their parts mirror other parts or rotate about an axis.
  • Repetition: The pattern repeats itself at regular intervals in three dimensions.
  • Geometry: The regularity of arrangement often gives rise to geometric shapes, allowing science to easily visualize and study them.

What is a unit cell?

The smallest repeating part of a crystal lattice is called a unit cell. In simple terms, if you can find a piece in the puzzle, which when repeated many times forms the whole puzzle, then it is similar to the unit cell in a crystal. By repeating and aligning the unit cell in different dimensions, one can form the complete crystal lattice.

The unit cell is defined by its lattice parameters, which include:

  • Lattice constants: These are the edge lengths of the unit cell, represented by a, b, and c.
  • Interaxial angles: These angles exist between the edges. They are represented by α (alpha), β (beta) and γ (gamma).

Types of unit cell

Unit cells are broadly classified into different types depending upon the symmetry features and length of the axes. There are three major types:

  • Primitive unit cell: Atoms are present only at the corners of the unit cell.
  • Body-centred unit cell: An extra atom is present at the centre of the unit cell along with the atoms located at the corners.
  • Face-centered unit cell: In addition to the corner atoms, additional atoms are present at the center of each face of the unit cell.

Understanding crystal systems

Each crystal system is formed by a combination of unit cells, which may show different symmetries and occupy different lattice positions. The set patterns in which the unit cells may be arranged are known as crystal systems, and seven such systems exist:

  • Triclinic: The most common crystal system in which all axes are different lengths and all angles are not equal to 90 degrees.
  • Monoclinic: Two axes have the same length, but two angles are 90 degrees, and the third angle is different.
  • Orthorhombic: all axes have different lengths, but all angles remain at 90 degrees.
  • Tetragonal: the two axes have the same length, and the angles are consistently at 90 degrees.
  • Cubic: The most common and simplest, with all axes the same length and all angles 90 degrees.
  • Hexagonal: Two dimensions of equal length are perpendicular, and the third forms a different angle.
  • Rhombus: All sides are equal, but none forms a right angle.

Crystal structure visualization

Visualizing crystals becomes easier when we break them down into these labeled geometric forms. Let's consider some 2D visual diagrams:

    
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        <circle cx="60" cy="100" r="10" fill="lightgrey" />
        <circle cx="100" cy="100" r="10" fill="lightgrey" />
    </svg>

Importance of crystal lattices and unit cells

Understanding crystal lattices and unit cells is important for a variety of reasons:

  • Predictive achievements: They help in predicting the properties of materials such as strength, conductivity, optical properties, etc.
  • Important for materials science: Their study is extremely important in materials science and for the development of new materials with unique properties.
  • The structural study of solids arises from these two basic concepts: the basis of chemistry and physics.

Conclusion

The extensive study of crystal lattices and unit cells in chemistry reveals the orderly and organized world at the atomic level in solids. These basic structures explain how nature beautifully arranges atoms to form structures ranging from simple ones like salt to complex ones like crystals. Understanding these basics paves the way for complex explorations in the field of physics, making advances in technology and industry possible.


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Crystal Lattice and Unit Cell

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