Grade 10
  1. Mechanics  1.1. Dynamics  1.1.1. Motion in one dimension  1.1.2. Motion in two dimensions  1.1.3. Displacement and Distance  1.1.4. Speed and Velocity  1.1.5. Acceleration  1.1.6. Graphical representation of motion  1.1.7. Equations of motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Projectile motion  1.1.10. Relative speed  1.2. Dynamics  1.2.1. Newton's Laws of Motion  1.2.2. Inertia and mass  1.2.3. Force and its types  1.2.4. action and reaction force  1.2.5. Friction and its effects  1.2.6. Coefficient of friction  1.2.7. Circular motion  1.2.8. Centripetal force and centripetal acceleration  1.2.9. Momentum and Impulse  1.2.10. Conservation of momentum  1.2.11. Newton's third law and applications  1.3. Work, Energy and Power  1.3.1. Work done by the force  1.3.2. Work–energy theorem  1.3.3. Kinetic energy  1.3.4. Potential energy  1.3.5. Mechanical energy  1.3.6. Energy Conservation  1.3.7. Power and efficiency  1.3.8. Renewable and non-renewable energy sources  1.4. Gravitational force  1.4.1. Newton's law of universal gravitation  1.4.2. Gravitational field and field strength  1.4.3. Acceleration due to gravity on different planets  1.4.4. Kepler's laws of planetary motion  1.4.5. Orbits and satellites  1.4.6. Weight and apparent weight  1.4.7. Gravitational potential energy
  2. Properties of matter  2.1. States of matter  2.1.1. Solid, liquid and gas  2.1.2. Molecular structure of matter  2.1.3. Intermolecular forces  2.1.4. Plasma and Bose–Einstein condensate  2.2. Pressure  2.2.1. Definition of Pressure  2.2.2. Pressure in liquids  2.2.3. Atmospheric pressure  2.2.4. Pascal's principle  2.2.5. Archimedes' Principle and Buoyancy  2.2.6. Surface tension and capillarity  2.3. Elasticity  2.3.1. Hooke's law  2.3.2. Stress and strain  2.3.3. Elastic Limit and Modulus of Elasticity  2.3.4. Applications of Elasticity
  3. Thermal physics  3.1. heat and temperature  3.1.1. Difference Between Heat and Temperature  3.1.2. Temperature scale  3.1.3. Thermal expansion  3.1.4. Thermal equilibrium  3.2. Heat transfer  3.2.1. Conductivity  3.2.2. Convection  3.2.3. Radiation  3.2.4. Insulation and its applications  3.3. Thermal properties of matter  3.3.1. Specific heat capacity  3.3.2. Latent heat and phase change  3.3.3. Boiling and Melting Point  3.3.4. Heat engines and refrigeration  3.4. Laws of Thermodynamics  3.4.1. Zeroth law of thermodynamics  3.4.2. First law of thermodynamics  3.4.3. Second law of thermodynamics  3.4.4. Carnot cycle
  4. Waves and optics  4.1. Nature and properties of waves  4.1.1. Types of waves in nature and properties of waves  4.1.2. Transverse and longitudinal waves  4.1.3. Wave parameters  4.1.4. Reflection and refraction of waves  4.1.5. Superposition and Interference  4.1.6. Standing Waves and Resonance  4.1.7. Doppler effect  4.2. Sound waves  4.2.1. Characteristics of sound waves  4.2.2. Speed of sound in different mediums  4.2.3. Applications of sound waves  4.2.4. Ultrasound and its uses  4.3. Light Waves and Optics  4.3.1. Nature of light  4.3.2. Reflection of light  4.3.3. Laws of reflection  4.3.4. Mirrors and Image Formation  4.3.5. Refraction of light  4.3.6. Snell's Law  4.3.7. Lenses and Image Formation  4.3.8. Total internal reflection and critical angle  4.3.9. Optical fibre  4.4. Optical Instruments  4.4.1. Microscope  4.4.2. Telescope  4.4.3. Human eye and vision defects  4.4.4. Camera and its working principle
  5. Electricity and Magnetism  5.1. Electrostatics  5.1.1. Electric charge and its properties  5.1.2. Conductors and Insulators  5.1.3. Coulomb's law  5.1.4. Electric field and field lines  5.1.5. Electric potential and potential difference  5.1.6. Capacitors and Capacitance  5.2. Current Electricity  5.2.1. Electric current and its measurement  5.2.2. Ohm's law  5.2.3. Resistance and resistivity  5.2.4. Series and Parallel Circuits  5.2.5. Electric power and energy  5.2.6. Kirchhoff's Laws  5.3. Magnetism and Electromagnetism  5.3.1. Magnetic field and field lines  5.3.2. Magnetic effects of electric current  5.3.3. Electromagnetic induction  5.3.4. Faraday's laws of electromagnetic induction  5.3.5. Transformers and Applications  5.3.6. AC and DC current
  6. Modern Physics  6.1. Nuclear physics  6.1.1. Structure of the atom  6.1.2. Bohr's atomic model  6.1.3. Electron Energy Levels  6.1.4. X-rays and applications  6.2. Radioactivity  6.2.1. Types of radiation  6.2.2. Half-life and radioactive decay  6.2.3. Nuclear reactions and applications  6.2.4. Fission and Fusion  6.3. Quantum physics  6.3.1. Wave–particle duality  6.3.2. Photoelectric effect  6.3.3. Energy quantization  6.3.4. Heisenberg's uncertainty principle
  7. Electronics and Communication  7.1. Semiconductors  7.1.1. Conductors, Insulators and Semiconductors  7.1.2. Diodes and their applications  7.1.3. Transistors and Logic Gates  7.1.4. LEDs and photodiodes  7.2. Communication Systems  7.2.1. Basics of communication  7.2.2. Analog and digital signals  7.2.3. Wireless and optical fibre communication  7.2.4. Radio Waves and Modulation

Grade 10 → Properties of matter → States of matter ↓


Intermolecular forces


Intermolecular forces are forces that arise between molecules. These forces have a profound effect on the physical properties of substances. Understanding these forces is important for understanding why different states of matter exist and how matter behaves under different conditions. In this explanation, we will explore the types of intermolecular forces, how they affect the properties of matter, and provide examples to make their effects more clear.

Types of intermolecular forces

There are several types of intermolecular forces that affect the behavior of molecules. The primary types include:

1. London dispersion force

London dispersion forces, also known as van der Waals forces, are the weakest type of intermolecular forces. They are caused by the transient random motion of electrons in atoms and molecules, creating temporary dipoles. These temporary dipoles induce dipoles in neighboring molecules, resulting in weak attraction.

temporary dipole

Since these forces arise due to momentary changes, they are prevalent in all molecules, especially in noble gases and nonpolar molecules.

2. Dipole-dipole interaction

Dipole-dipole interactions occur between molecules that have permanent dipoles. Molecules with polar bonds have a slight charge imbalance, with one atom being slightly negative and the other slightly positive. These polarized molecules align themselves in such a way that the positive end of one molecule is near the negative end of the other.

δ+δ-Dipole–dipole

These forces are stronger than London dispersion forces but weaker than hydrogen bonds. An example of this is the interaction between hydrochloric acid (HCl) molecules.

3. Hydrogen bonds

A hydrogen bond is a special type of dipole-dipole interaction in which hydrogen is bound to a more electronegative atom such as nitrogen, oxygen, or fluorine. This bond results in a highly polar bond, which in turn facilitates unusually strong dipole attractions with other molecules.

H₂OH-bonding

Water is the most common example where hydrogen bonding is evident, giving water unique properties such as a high boiling point and surface tension.

States of matter and intermolecular forces

The state of matter (solid, liquid or gas) is greatly affected by the strength of intermolecular forces. Below is a description of each state related to these forces:

Solids

The particles in solids are tightly packed together in a regular arrangement. The force of attraction is so strong that the particles remain fixed in place, vibrating only slightly. This results in a definite shape and volume.

Solid Structure

Examples of solids include ice, metals, and minerals. The strong intermolecular forces present in these substances make them hard and rigid.

Liquids

In liquids, intermolecular forces are weaker than in solids, allowing particles to slide past one another, so liquids have definite volume but indefinite shape. They can flow and take the shape of their container.

Liquid composition

Liquids such as water, oil, and mercury have properties such as viscosity and surface tension, which are mainly due to intermolecular forces.

Gases

Intermolecular forces are weakest in gases. The particles are far apart and move around freely, as a result of which they have no definite shape or volume. They expand to fill whatever container they are in.

Gas Composition

Gaseous substances such as oxygen, nitrogen, and carbon dioxide exhibit high compressibility and low density due to weak intermolecular forces.

Factors affecting intermolecular forces

Several factors affect the strength and type of intermolecular forces in substances:

1. Molecular size

Larger molecules have greater London dispersion forces due to more electrons and thus, are more likely to produce dipoles in adjacent molecules.

For example, heavier noble gases such as xenon (Xe) exhibit stronger London dispersion forces than lighter noble gases such as neon (Ne).

2. Molecular shape

The shape of a molecule can increase or decrease dipole interactions. Long, thin molecules can align with each other more efficiently, resulting in stronger interactions, while bulky molecules have a smaller interaction surface area.

3. Polarity

Molecules with more polar bonds have stronger dipole-dipole interactions. Individual bond dipoles can combine to make the molecule more polar, as seen in water (H₂O).

Applications and real-life examples

Intermolecular forces play an important role in everyday life and in a variety of scientific fields:

Boiling and melting point

Substances with stronger intermolecular forces require more energy (in the form of heat) to overcome these forces, resulting in higher boiling and melting points. This concept is important when distilling liquids or creating materials with specific thermal properties.

Surface tension

Liquids such as water exhibit surface tension due to hydrogen bonding, allowing small insects to walk on water or droplets to form beads on smooth surfaces.

Stickiness

Liquids with strong intermolecular forces, such as honey or glycerin, exhibit high viscosity, making them thick and resistant to flow.

Solubility

The concept of "like dissolves like" is based on intermolecular forces. Polar substances dissolve well in polar solvents because of the same type of intermolecular forces.

Biological molecules

Intermolecular forces are important in biological systems. For example, DNA strands are held together by hydrogen bonds, making the double-helix structure possible.

Conclusion

Intermolecular forces are a fundamental aspect of chemistry and physics, which determine how substances behave in different states of matter. Understanding these forces helps explain a variety of phenomena in nature and industry, from the phases of elements and compounds to the complex structures of biomolecules. By studying intermolecular forces, we gain insight into the hidden forces that shape our physical world.


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Intermolecular forces

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