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Chapter 4 – Atomic Structure

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:


The first theory on the structure of the atom was given by John Dalton in the 1800s. The research on the structure of an atom gave us a lot of information about various chemical reactions and physical characteristics of an atom. You might have come across this simple observation that atoms exist all around in the universe and undergo various chemical reactions. To understand them, we need to know the atomic structure and its properties.

The structure of atoms around us comprises a systematic collection of nuclear particles. The negatively charged particles around the nucleus are called electrons. The neutrons and protons together constitute the nucleus of an atom. The electrons of the atom always surround this nucleus.

We can also define the atomic number of an atom as the total number of protons present in its specific nucleus. Neutral atoms are atoms that have an equal number of electrons and protons in them. Every atom gains or loses its electrons to increase its stability. The atoms that are of various elements have a different atomic structure. Every atom of an additional component has a different number of electrons and protons.

In earlier centuries, various scientists tried to work on the atomic structure. They attempted this study with the help of various atomic models. Every model has different advantages and disadvantages. The most appropriate atomic model was proposed by John Dalton, Niels Bohr, J.J. Thompson, and Ernest Rutherford.

John Dalton was an English chemist. He proposed that all the matter around us is composed of atoms. He also suggested that these atoms are indivisible as well as indestructible. According to Dalton, the same elements are identical, whereas the atoms of different elements are not the same in physical and chemical properties.

  • Every matter around us is made of atoms.
  • Atoms cannot be divided.
  • The same type of element contains the same kind of atoms.
  • Every element has a specific type of atom in it.
  • Every atom has a particular mass number.
  • All atoms undergo specific chemical reactions.
  • You can neither create nor destroy an atom.

Daltons’ atomic theory also brought up laws of mass conservation, multiple proportions, and reciprocal proportions.

  • Dalton’s atomic theory was not able to justify the presence of isotopes.
  • The approach did not explain the structure of the atom adequately.
  • The scientists were also able to discover that atoms are divisible.

In the 1900s, Sir Joseph John Thomson presented his atomic structure model. He also won the Nobel Prize for the discovery of negatively charged particles called electrons with these experiments. He worked on the investigation known as the experiment of cathode rays.

  • Neutrons
    The mass of a proton and a neutron is approximately the same, i.e., 1.674×10-24. Neutrons do not have any charge on them. They are neutral.
  • Protons
    Protons refer to the positively charged particles in the atom. The charge on a proton is 1e. 1e equals 1.602 × 10-19 Mass of a proton is 1.672×10-24. Protons are more decadent than electrons. The number of protons in an atom is equal to the atomic number of that specific element.
  • Electrons
    The mass of an electron is around 9.1 × 10-31.Electrons do not contribute to the mass of an atom as they have a very negligible mass.The charge on an electron is -1e, i.e., approximately -1.602 × 10-19.

According to the given constraints, all the electrons are supposed to fill in the s, p, d, f orbitals:

  1. Aufbau’s principle: According to this rule, the filling of electrons of an atom should take place according to the ascending order of energy of these orbitals:
    • The orbitals with lower energy should fill first compared to the orbitals with higher energy levels.
    • The orbital energy level is α(p + l) value if any two orbitals have a similar (n + l) value.
    • Ascending order of energy levels is 1s, 2s, 2p, 3s, 3p, 4s, 3d,…
  2. Hund’s rule of maximum multiplicity: According to this rule, in the case of the filling process of the same energy orbitals, all orbitals must be singly filled at first.
  3. Pauli’s exclusion principle: According to this rule, no two electrons can have all four quantum numbers as the same value. However, if two electrons are present in the same state of energy, they must have opposite spin.

The atomic structure comprises the nucleus, protons, and neutrons. An atom also includes negatively charged particles called electrons which always revolve around the nucleus. Democritus was the first man who brought up the concept of atomic structure and quantum mechanics. He proposed for the first time that matter comprises atoms. Since then, many atomic models were proposed, leading to the discovery of subatomic particles and their properties.

  1. What do you mean by subatomic particles?
    Subatomic particles are the particles that comprise the atom. It refers to the electrons, protons, and neutrons.
  2. What is the difference between the atomic structures of isotopes?
    The atomic structures of isotopes have a different number of neutrons in their nucleus. It is also referred to as nucleon numbers.
  3. What are isotopes?
    Isotopes refer to the various types of elements with different neutrons and the same number of protons.
  4. What do you mean by mass number?
    The mass number of an atom is the sum of several neutrons and protons.
  5. What is an atomic number of an atom?
    The atomic number of an element is the number of protons.

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High School Physics

  • Alternating Current
  • Atoms
  • Communication Systems
  • Current Electricity
  • Dual nature of Radiation and Matter
  • Electric Charges and Fields
  • Electricity
  • Electromagnetic Induction
  • Electromagnetic Waves
  • Electron Beams and Radioactivity
  • Electrons and Photons
  • Electrostatic Potential and Capacitance
  • Fluid Pressure
  • Force and Acceleration
  • Force And Laws Of Motion
  • Gravitation
  • Internal Energy
  • Kinetic Theory
  • Law of motion
  • Light – Reflection And Refraction
  • Magnetic Effects Of Electric Current
  • Magnetism and Matter
  • Management Of Natural Resources
  • Mechanical properties of Fluids
  • Mechanical properties of Solids
  • Motion
  • Motion in a plane
  • Motion in a straight line
  • Moving Charges and Magnetism
  • Nuclear Energy
  • Nuclei
  • Oscillations
  • Our Environment
  • Paths of Heat
  • Physical world
  • Ray optics and optical instruments
  • Semiconductor Devices
  • Semiconductor Electronics: Materials, Devices and Simple Circuits
  • Simple Machines
  • Sound
  • Sources Of Energy
  • Specific and Latent Heats
  • Spherical Mirrors
  • Static Electricity
  • Systems of Particles and Rotational motion
  • Thermal properties of matter
  • Thermodynamics
  • Units and Measurement
  • Vectors, Scalar Quantities and Elementary Calculus
  • Wave Optics
  • Waves
  • Work, Power and Energy

High School Chemistry

  • Acids, Bases and Salts
  • Alcohols, Phenols and Ethers
  • Aldehydes, Ketones and Carboxylic Acids
  • Aliphatic and Aromatic Hydrocarbons
  • Alkyl and Aryl Halides
  • Amines
  • Analytical Chemistry 
  • Atomic Structure
  • Atoms And Molecules
  • Basic concepts of Chemistry
  • Biomolecules
  • Carbon And Its Compounds
  • Carboxylic acids and Acid Derivatives
  • Chemical Bonding and Molecular Structures
  • Chemical Energetics
  • Chemical Equilibria
  • Chemical Kinetics
  • Chemical Reactions And Equations
  • Chemical Reactions and Their Mechanisms
  • Chemistry in Everyday Life
  • Chemistry of p-Block elements
  • Chemistry of Transition and Inner Transition
  • Classification of Elements
  • Coordination Compounds
  • Cyanide, Isocyanide, Nitro compounds and Amines
  • Electrochemistry
  • Electrolysis
  • Elements, Compounds and Mixtures
  • Environmental Chemistry
  • Equilibrium
  • Ethers and Carbonyl compounds
  • Haloalkanes and Haloarenes
  • Hydrocarbons
  • Hydrogen
  • Ideal solutions
  • Introduction to Organic Chemistry
  • Ionic equilibria
  • Matter
  • Matter Around Us
  • Matter In Our Surroundings
  • Metallurgy
  • Metals And Non-Metals
  • Mole Concept and Stoichiometry
  • Natural Resources
  • Organic Chemistry – Basic Principles
  • Periodic Classification of Elements
  • Physical and Chemical Changes
  • Physical and Chemical Properties of Water
  • Polymers
  • Preparation, Properties and Uses of Compounds
  • Principles and Processes of Isolation of Elements
  • Redox Reactions
  • Relative Molecular Mass and Mole
  • States of Matter
  • Structure Of The Atom
  • Study of Compounds
  • Study of Gas Laws
  • Study of Representative Elements
  • Surface Chemistry
  • The d-block and f-block elements
  • The Gaseous State
  • The p-Block Elements
  • The Periodic Table
  • The s-Block Elements
  • The Solid State
  • Thermodynamics

High School Biology

  • Absorption and Movement of Water in Plants
  • Adolescent Issues
  • Anatomy of Flowering Plants
  • Animal Kingdom
  • Bacteria and Fungi-Friends and Foe
  • Biodiversity and Conservation
  • Biofertilizers
  • Biological Classification
  • Biomedical Engineering
  • Biomolecules
  • Biotechnology and its Applications
  • Biotic Community
  • Body Fluids and Circulation
  • Breathing and Exchange of Gases
  • Cell – Unit of Life
  • Cell Cycle and Cell Division
  • Cell Division and Structure of Chromosomes
  • Cell Reproduction
  • Cellular Respiration
  • Chemical Coordination and Integration
  • Circulation
  • Control And Coordination
  • Crop Improvement
  • Digestion and Absorption
  • Diversity In Living Organisms
  • Ecosystem
  • Environmental Issues
  • Excretory Products and their Elimination
  • Flowering Plants
  • Genes and Chromosomes
  • Health and Diseases
  • Health and Its Significance
  • Heredity And Evolution
  • Heredity and Variation
  • How Do Organisms Reproduce?
  • Human Diseases
  • Human Eye And Colourful World
  • Human Health and Disease
  • Human Population
  • Human Reproduction
  • Hygiene
  • Improvement In Food Resources
  • Integumentary System- Skin
  • Kingdom Fungi
  • Kingdom Monera
  • Kingdom Protista
  • Life Processes
  • Locomotion and Movement
  • Microbes in Human Welfare
  • Mineral Nutrition
  • Molecular Basis of Inheritance
  • Morphology of Flowering Plants
  • Neural Control And Coordination
  • Nutrition in Human Beings
  • Organism and Population
  • Photosynthesis
  • Photosynthesis in Higher Plants
  • Plant Growth and Development
  • Plant Kingdom
  • Pollination and Fertilization
  • Pollution; Sources and its effects
  • Principles of Inheritance and Variation
  • Reproduction and Development in Angiosperms
  • Reproduction in Organisms
  • Reproductive Health
  • Respiration in Human Beings
  • Respiration in Plants
  • Respiratory System
  • Sexual Reproduction in Flowering Plants
  • Strategies for Enhancement in Food Production
  • Structural Organisation in Animals
  • Structural Organisation of the Cell
  • The Endocrine System
  • The Fundamental Unit Of Life
  • The Living World
  • The Nervous System and Sense Organs
  • Tissues
  • Transpiration
  • Transport in Plants

High School Math

  • Algebra – Arithmatic Progressions
  • Algebra – Complex Numbers and Quadratic Equations
  • Algebra – Linear Inequalities
  • Algebra – Pair of Linear Equations in Two Variables
  • Algebra – Polynomials
  • Algebra – Principle of Mathematical Induction
  • Algebra – Quadratic Equations
  • Binomial Theorem
  • Calculus – Applications of Derivatives
  • Calculus – Applications of the Integrals
  • Calculus – Continuity and Differentiability
  • Calculus – Differential Equations
  • Calculus – Integrals
  • Geometry – Area
  • Geometry – Circles
  • Geometry – Conic Sections
  • Geometry – Constructions
  • Geometry – Introduction to Euclid’s Geometry
  • Geometry – Three-dimensional Geometry
  • Geometry – Lines and Angles
  • Geometry – Quadrilaterals
  • Geometry – Straight Lines
  • Geometry – Triangles
  • Linear Programming
  • Matrices and Determinants
  • Mensuration – Areas
  • Mensuration – Surface Areas and Volumes
  • Number Systems
  • Number Systems – Real Numbers
  • Permutations and Combinations
  • Probability
  • Sequence and Series
  • Sets and Functions
  • Statistics 
  • Trignometry – Height and Distance
  • Trignometry – Identities
  • Trignometry – Introduction

Middle School Science

  • Acids, Bases And Salts
  • Air and Its Constituents
  • Basic Biology
  • Body Movements
  • Carbon and Its Compounds
  • Cell – Structure And Functions
  • Changes Around Us
  • Chemical Effects Of Electric Current
  • Chemistry in Your Life
  • Coal And Petroleum
  • Combustion And Flame
  • Components Of Food
  • Conservation Of Plants And Animals
  • Crop Production And Management
  • Electric Current And Its Effects
  • Electricity And Circuits
  • Elements and Compounds
  • Fibre To Fabric
  • Food production and management
  • Force And Pressure
  • Forests: Our Lifeline
  • Friction
  • Fun With Magnets
  • Garbage In, Garbage Out
  • Getting To Know Plants
  • Health and Hygiene
  • Heat
  • Hydrogen
  • Life Processes: Nutrition in Animals and Plants
  • Light, Shadows And Reflections
  • Materials: Metals And Non-Metals
  • Matter and Its States
  • Metals and Non-metals
  • Micro Organisms: Friend And Foe
  • Motion And Measurement Of Distances
  • Motion And Time
  • Nutrition In Animals
  • Nutrition In Plants
  • Organization in Living Things
  • Our Environment
  • Physical And Chemical Changes
  • Pollution and conservation
  • Pollution Of Air And Water
  • Reaching The Age Of Adolescence
  • Reproduction In Animals
  • Reproduction In Plants
  • Respiration In Organisms
  • Rocks and Minerals
  • Separation Of Substances
  • Simple Machines
  • Soil
  • Some Natural Phenomena
  • Sorting Materials Into Groups
  • Sound
  • Stars And The Solar System
  • Structure of Atom
  • Synthetic Fibers And Plastics
  • The Living Organisms And Their Surroundings
  • Transfer of Heat
  • Transformation of Substances
  • Transportation In Animals And Plants
  • Universe
  • Waste-water Story
  • Water: A Precious Resource
  • Weather, Climate And Adaptations Of Animals To Climate
  • Winds, Storms And Cyclones

Middle School Math

  • Addition
  • Area and Its Boundary
  • Boxes and Sketches
  • Data Handling
  • Fun With Numbers
  • Heavy and Light
  • How Many
  • Long And Short
  • Mapping
  • Measurement
  • Money
  • Multiplication and Factors
  • Multiply and Divide
  • Numbers
  • Parts and Wholes
  • Pattern Recognition
  • Patterns
  • Play With Patterns
  • Rupees And Paise
  • Shapes And Angles
  • Shapes And Designs
  • Shapes and Space
  • Similarity
  • Smart Charts
  • Squares
  • Subtraction
  • Tables And Shares
  • Tenths and Hundredths
  • Time
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