| Year | Scientist / Model | Key Points |
|---|---|---|
| 1808 | John Dalton – Dalton’s Atomic Theory | • Matter made of indivisible atoms. • Atoms of same element are identical. • Chemical reactions involve rearrangement of atoms. |
| 1897 | J. J. Thomson – Discovery of Electron | • Discovered electron using cathode ray experiment. • Measured charge-to-mass ratio (e/m) of electron. |
| 1904 | J. J. Thomson – Plum Pudding Model | • Atom is positively charged sphere with electrons embedded inside. |
| 1909 | Robert A. Millikan – Oil Drop Experiment | • Measured charge of electron (1.6 × 10⁻¹⁹ C). |
| 1911 | Ernest Rutherford – Rutherford Atomic Model | • Gold foil experiment discovered nucleus. • Most of atom is empty space. |
| 1913 | Niels Bohr – Bohr Atomic Model | • Electrons revolve in fixed energy levels (shells). • Energy levels are quantized. |
| 1924 | Louis de Broglie – Wave Nature of Electron | • Proposed wave–particle duality of electrons. |
| 1926 | Erwin Schrödinger – Quantum Mechanical Model | • Electrons described by wave functions and orbitals. |
| 1927 | Werner Heisenberg – Uncertainty Principle | • Exact position and momentum of electron cannot be known simultaneously. |
| Year | Concept | Key Points |
|---|---|---|
| 1900 | Max Planck – Quantum Theory | Energy emitted in discrete packets called quanta. |
| 1905 | Albert Einstein – Photoelectric Effect | Light behaves as particles (photons). |
| 1924 | Louis de Broglie – Matter Waves | All matter particles have wave nature. |
| 1927 | Werner Heisenberg – Uncertainty Principle | Position and momentum cannot be measured simultaneously with perfect accuracy. |
| Year | Scientist / Law | Key Statement / Concept |
|---|---|---|
| 1789 | Antoine Lavoisier – Law of Conservation of Mass | • Mass is neither created nor destroyed in a chemical reaction. • Total mass of reactants = total mass of products. |
| 1799 | Joseph Proust – Law of Definite Proportions | • A compound always contains same elements in fixed ratio by mass. |
| 1803 | John Dalton – Law of Multiple Proportions | • If two elements form more than one compound, the ratio of masses combining is a simple whole number ratio. |
| 1808 | John Dalton – Dalton’s Atomic Theory | • Matter consists of indivisible atoms. • Atoms combine in simple ratios to form compounds. |
| 1808 | Joseph Louis Gay-Lussac – Law of Combining Volumes | • Volumes of reacting gases combine in simple whole-number ratios at same temperature and pressure. |
| 1811 | Amedeo Avogadro – Avogadro’s Law | • Equal volumes of gases at same temperature and pressure contain equal number of molecules. |
| 1911 | Ernest Rutherford – Rutherford Atomic Model | • Atom has small dense nucleus with electrons revolving around it. |
| 1913 | Niels Bohr – Bohr Atomic Model | • Electrons move in fixed energy levels (orbits) around nucleus. |
| 1924 | Louis de Broglie – de Broglie Hypothesis | • Electrons have wave–particle dual nature. |
| 1926 | Erwin Schrödinger – Wave Equation / Quantum Model | • Electrons described by probability orbitals (wave function). |
| 1927 | Werner Heisenberg – Uncertainty Principle | • Exact position and momentum of electron cannot be known simultaneously. |
| Year | Scientist / Discovery | Key Points |
|---|---|---|
| 1897 | J. J. Thomson – Discovery of Electron | • Discovered using cathode ray tube experiment. • Showed atoms contain negatively charged particles (electrons). |
| 1904 | J. J. Thomson – Plum Pudding Model | • Atom is a positively charged sphere with electrons embedded inside like “plums”. |
| 1909 | Robert A. Millikan – Oil Drop Experiment | • Measured charge of electron (1.6 × 10⁻¹⁹ C). |
| 1911 | Ernest Rutherford – Nuclear Model of Atom | • Proposed central nucleus with electrons revolving around it. |
| 1913 | Niels Bohr – Bohr Atomic Model | • Electrons move in fixed energy levels (shells) around nucleus. |
| 1924 | Louis de Broglie – Wave Nature of Electron | • Electrons have wave–particle duality. |
| 1926 | Erwin Schrödinger – Quantum Mechanical Model | • Electrons exist in orbitals (probability regions) rather than fixed paths. |
| 1927 | Werner Heisenberg – Uncertainty Principle | • Exact position and momentum of an electron cannot be known simultaneously. |
| 1928 | Paul Dirac – Dirac Equation | • Predicted existence of antimatter (positron) and relativistic behavior of electrons. |
| Year | Scientist / Discovery | Key Points |
|---|---|---|
| 1886 | Eugen Goldstein – Canal Rays (Anode Rays) | • Discovered positively charged rays in discharge tube. • These rays led to the discovery of positive particles (protons). |
| 1911 | Ernest Rutherford – Nuclear Model of Atom | • Proposed that atom has a dense positively charged nucleus. |
| 1917 | Ernest Rutherford – Discovery of Proton | • Identified hydrogen nucleus as a fundamental particle (proton). • Discovered during nitrogen bombardment experiment. |
| 1919 | Ernest Rutherford – Artificial Nuclear Transmutation | • First artificial nuclear reaction converting nitrogen into oxygen. |
| 1920 | Ernest Rutherford – Naming of Proton | • Proposed the name “proton” for the hydrogen nucleus. |
| Year | Scientist / Discovery | Key Points |
|---|---|---|
| 1920 | Ernest Rutherford – Prediction of Neutron | • Suggested the existence of a neutral particle in the nucleus. • Proposed to explain atomic mass not accounted for by protons. |
| 1932 | James Chadwick – Discovery of Neutron | • Discovered neutron by bombarding beryllium with alpha particles. • Confirmed the existence of neutral particle in nucleus. |
| 1934 | Enrico Fermi – Neutron Bombardment Experiments | • Used neutrons to produce artificial radioactivity. • Showed neutrons are effective for nuclear reactions. |
| 1938 | Otto Hahn & Fritz Strassmann – Nuclear Fission Discovery | • Found that uranium splits into lighter elements when bombarded with neutrons. |
| 1939 | Lise Meitner & Otto Frisch – Explanation of Nuclear Fission | • Explained the fission process and energy release due to neutron reaction. |
| Year | Scientist / Law | Key Points |
|---|---|---|
| 1817 | Johann Wolfgang Döbereiner – Döbereiner’s Triads | • Elements grouped in sets of three (triads) with similar properties. • Atomic mass of middle element ≈ average of other two. |
| 1862 | Alexandre-Émile Béguyer de Chancourtois – Telluric Screw | • First attempt to arrange elements by atomic weight in spiral form. |
| 1864 | John Newlands – Law of Octaves | • Every 8th element shows similar properties when arranged by increasing atomic mass. |
| 1869 | Dmitri Mendeleev – Periodic Law / Periodic Table | • Elements arranged according to increasing atomic mass. • Properties repeat periodically. • Left gaps for undiscovered elements. |
| 1913 | Henry Moseley – Modern Periodic Law | • Elements arranged by increasing atomic number instead of atomic mass. |
| 1944 | Glenn T. Seaborg – Actinide Concept | • Proposed separate actinide series below lanthanides. • Helped create the modern periodic table layout. |