Grade 9
  1. Mechanics  1.1. Motion  1.1.1. Types of motion  1.1.2. Distance and displacement  1.1.3. Speed and Velocity  1.1.4. Acceleration  1.1.5. Graphical representation of motion  1.1.6. Equations of motion  1.1.7. Uniform and non-uniform motion  1.1.8. Free fall and acceleration due to gravity  1.1.9. Relative speed  1.1.10. Circular motion  1.2. Laws of force and motion  1.2.1. The concept of force  1.2.2. newton's first law of motion  1.2.3. Newton's second law of motion  1.2.4. Newton's third law of motion  1.2.5. Inertia and types of inertia  1.2.6. Motion  1.2.7. Conservation of momentum  1.2.8. Application of Newton's laws in daily life  1.2.9. Types of Forces (Contact and Non-Contact)  1.2.10. Friction and its effects  1.3. Gravitational force  1.3.1. Newton's law of universal gravitation  1.3.2. Importance of Gravitational Force  1.3.3. Acceleration due to gravity  1.3.4. Free fall and weightlessness  1.3.5. Mass and weight  1.3.6. Variation of g with height and depth  1.3.7. Kepler's laws of planetary motion  1.3.8. Satellites and their orbits  1.4. Work, Energy and Power  1.4.1. Concept of work  1.4.2. Positive and negative actions  1.4.3. Work done by constant and variable force  1.4.4. Energy and its forms  1.4.5. Kinetic energy and potential energy  1.4.6. Law of conservation of energy  1.4.8. Commercial unit of energy  1.4.9. Work–energy theorem  1.5. Simple machines  1.5.1. Types of simple machines  1.5.2. Mechanical advantage  1.5.3. Machine efficiency  1.5.4. Levers and their types  1.5.5. Pulleys and Inclined Planes  1.5.6. Gears and their uses
  2. Properties of matter  2.1. States of matter  2.1.1. Solids, liquids and gases  2.1.2. Properties of different states of matter  2.1.3. Change in state of matter  2.1.4. Plasma and Bose–Einstein condensate  2.2. Density and pressure  2.2.1. Concept of density and relative density  2.2.2. Pressure in solids, liquids and gases  2.2.3. Pascal's law and its applications  2.2.4. Atmospheric pressure and its variations  2.2.5. Surface tension and capillarity  2.3. Buoyancy and Archimedes' principle  2.3.1. Buoyant force  2.3.2. Archimedes principle  2.3.3. Applications of Archimedes' Principle  2.3.4. floating and sinking objects  2.3.5. Theory of Flotation and Archimedes' Principle
  3. Heat and Thermodynamics  3.1. Temperature and heat  3.1.1. Concept of heat and temperature  3.1.2. Temperature measurement  3.1.3. Temperature scales  3.2. Heat transfer  3.2.1. Conduction of heat  3.2.2. Convection of heat  3.2.3. heat radiation  3.2.4. Applications of heat transfer  3.2.5. Thermal conductivity  3.3. Thermal expansion  3.3.1. Expansion of solids, liquids and gases  3.3.2. Abnormal expansion of water  3.3.3. Applications of Thermal Expansion  3.4. Specific heat capacity and latent heat  3.4.1. Concept of specific heat capacity  3.4.2. Measurement and applications of specific heat  3.4.3. Latent heat of fusion and vaporization  3.4.4. Heat Engines and Efficiency
  4. Waves and sound  4.1. Waves and their types  4.1.1. Mechanical and electromagnetic waves  4.1.2. Longitudinal and Transverse Waves  4.1.3. Properties of Waves  4.1.4. Wavelength, frequency and speed of the wave  4.1.5. Superimposition of waves  4.2. Sound waves  4.2.1. Nature and transmission of sound  4.2.2. Speed of sound in different mediums  4.2.3. Reflection of sound and echo  4.2.4. Sonar and ultrasound  4.2.5. Resonance and pulsation  4.3. Sound characteristics  4.3.1. Intensity, loudness and quality of sound  4.3.2. Doppler effect in sound
  5. Lighting and Optics  5.1. Reflection of light  5.1.1. Laws of reflection  5.1.2. Reflection from a plane mirror  5.1.3. Reflection from a spherical mirror  5.1.4. Image formation by concave and convex mirrors  5.1.5. Applications of Reflection  5.2. Refraction of light  5.2.1. Laws of refraction  5.2.2. Refractive index  5.2.3. Refraction through a glass slab  5.2.4. Refraction in water and air  5.2.5. Lenses and their types  5.2.6. Image formation by convex and concave lenses  5.2.7. Total internal reflection and its applications  5.3. Dispersion and scattering of light  5.3.1. Spectrum of white light  5.3.2. Prisms and Dispersion  5.3.3. Tyndall effect and blue sky
  6. Electricity and Magnetism  6.1. Electric charge and static electricity  6.1.1. The concept of electric charge  6.1.2. Charging by friction, contact and induction  6.1.3. Electroscope and its working  6.2. Current Electricity  6.2.1. The concept of electric current  6.2.2. Ohm's Law and Resistance  6.2.3. Factors affecting resistance  6.2.4. Series and Parallel Circuits  6.2.5. Heating effect of electric current  6.2.6. Electric power and energy  6.3. Magnetism  6.3.1. Natural and artificial magnets  6.3.2. Properties of magnets  6.3.3. Earth's magnetism  6.3.4. Magnetic field and field lines  6.3.5. Electromagnets and their applications
  7. Modern Physics  7.1. structure of the atom  7.1.1. Atomic Structure and Subatomic Particles  7.1.2. Electrons, Protons, and Neutrons  7.1.3. Rutherford and Bohr model  7.2. Radioactivity  7.2.1. Types of radioactive emissions  7.2.2. Half-life and radioactive decay  7.2.3. Uses and Hazards of Radioactivity
  8. Space science and astronomy  8.1. The universe and its components  8.1.1. Stars and galaxies  8.1.2. Planets and Solar System  8.2. Satellites  8.2.1. Natural and artificial satellites  8.2.2. Use of satellites

Grade 9 → Modern Physics → structure of the atom ↓


Electrons, Protons, and Neutrons


Atoms are the building blocks of matter, and they are incredibly small. Each atom is made up of three main types of tiny particles called subatomic particles. These particles are electrons, protons, and neutrons. Understanding these particles is important for knowing the structure of matter and how atoms work in the universe. Atoms are so small that a single drop of water contains about 1.39 sextillion atoms.

Structure of the atom

The basic structure of an atom consists of a central nucleus and a ring of electrons. The nucleus, which is located at the center of the atom, contains protons and neutrons. Electrons orbit around the nucleus in regions called electron shells or orbitals.

Proton

Protons are positively charged particles found in the nucleus of an atom. Each proton has a positive charge of +1e, where e represents the elementary charge, which is approximately 1.602 x 10 -19 coulombs. The number of protons in an atom's nucleus is called the atomic number, which uniquely identifies an element. For example, hydrogen has one proton, so its atomic number is 1, and carbon has six protons, giving it an atomic number of 6.

Proton+1

Protons are important not only for giving elements their identity, but also for the mass of the atom. Protons, together with neutrons, account for almost the entire mass of the atom. Despite the proton's small size - its radius is about 8.8 x 10 -16 meters - it is much heavier than the electron.

Neutron

Neutrons are neutral particles, which means they have no electrical charge. They are also found in the nucleus along with protons. Neutrons perform several important functions in the nucleus of an atom. They stabilize the nucleus by reducing the electrostatic repulsion between the positively charged protons. Without neutrons, many atomic nuclei would not be able to hold together because of the repulsion forces between the protons.

Neutron0

The number of neutrons in the nucleus of an atom can vary even among atoms of the same element. When atoms of the same element have different numbers of neutrons, they form isotopes. For example, hydrogen has isotopes such as deuterium and tritium, which have one and two neutrons, respectively. Like protons, neutrons also contribute significantly to the atomic mass. Interestingly, neutrons are slightly heavier than protons.

Electrons

Electrons are negatively charged particles that orbit the nucleus of an atom. They carry a charge of -1e. Electrons are much smaller and lighter than protons and neutrons, with a mass of about 1/1836 that of a proton. Despite their small size, electrons are important to the chemical properties of an atom.

Electron-1

Electrons reside in regions called electron shells that surround the nucleus. These shells are organized into energy levels and determine how an atom interacts with others. Electrons are involved in forming chemical bonds. For example, in a water molecule, electrons are shared between the hydrogen and oxygen atoms, keeping them bonded.

The behavior of electrons is explained by quantum mechanics. Electrons are described as occupying "orbitals," which are regions where the electron is most likely to be found. This is often referred to as the electron cloud. Electrons revolve around the nucleus so quickly that they create a cloud-like appearance due to their presence in different locations at any given time.

Interaction between electron, proton and neutron

Protons and electrons have opposite charges, resulting in an attractive force between them. This force is called the electromagnetic force, and it helps keep electrons bound to the nucleus. This force is important for the stability of the atom, because it causes electrons to travel in certain energy levels around the nucleus. These energy levels determine how atoms will connect to each other to form molecules.

Neutrons have no charge, so they do not play a direct role in binding electrons. Instead, neutrons contribute to the stability of the nucleus. The strong nuclear force, one of the four fundamental forces in nature, binds the protons and neutrons together in the nucleus. This force is much stronger than the electromagnetic force, but acts over very short distances, comparable to the size of the nucleus.

Historical development

Our understanding of the atom and its components has evolved over time. The concept of the atom as a fundamental unit of matter dates back to ancient Greece. However, the modern understanding began in the early 20th century. Ernest Rutherford's gold foil experiment revealed a dense, positively charged nucleus, leading to the Rutherford model of the atom.

Niels Bohr expanded this model by introducing the idea of quantized electron shells or energy levels around the nucleus. This development was a significant advance in atomic theory and laid the groundwork for modern quantum physics.

Further research in the mid-20th century by scientists such as James Chadwick, who discovered the neutron, refined the atomic model into what we understand today.

Conclusion

Atoms are the fundamental units that compose all forms of matter. The elementary subatomic particles, electrons, protons, and neutrons, are essential to the formation and properties of atoms. Protons and neutrons make up the nucleus and determine the identity and isotopic characteristics of an element, while electrons control an atom's chemical behavior and bond formation.

Understanding these particles and their interactions provides information about the microscopic world that forms the basis of much of modern science. This fundamental knowledge is not only an exciting field of study, but is also essential for advances in technology, chemistry, and physics.


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Electrons, Protons, and Neutrons

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