EVOLUTION OF ATOMIC MODELS

1. Evolution of atomic structure : General Chemisty Presented by : pulak maity, M. Sc. Iitdelhi

2. Prologue The concept of the atom has fascinated scientists for centuries. Over time, our understanding of atomic structure has evolved through groundbreaking discoveries and scientific theories. Let's embark on a journey through the evolution of the atomic model. Presented by : pulak maity i Image : ScinceABC

3. John Dalton (1803) : billiard ball model • Atoms were considered indivisible and uniform spheres. • Elements were composed of atoms with different masses and properties. • Chemical reactions involved the rearrangement of atoms. Presented by : pulak maity Image : Symbols of different elements. Source : Brilliant.org

4. RADIOACTIVITY • Radioactive elements are unstable and undergo spontaneous breakdown from one chemical atom to another with the commission of either charged α-particle or ß-particle. • Radioactivity demonstrated that the atom was neither indivisible nor immutable. Source : rinconeducativo.org Presented by : pulak maity

5. Thomson's Plum Pudding Model (1897) • J.J. Thomson discovered the electron studying cathode ray. • Proposed the Plum Pudding Model. • Atoms were composed of positively charged "pudding" with negatively charged electrons embedded like "plums." • This model explained the existence of negatively charged particles. Presented by : pulak maity Source : twitter

6. Rutherford's Nuclear Model (1911) • Ernest Rutherford conducted the gold foil experiment. • Discovered the atomic nucleus and proposed the Nuclear Model. • Atoms consisted of a small, dense, positively charged nucleus. • Electrons orbited around the nucleus, which contain proton, another sub-atomic paricles. • The majority of an atom's volume was empty space. • It failed to explain the stability of an atom. Presented by : pulak maity Source : researchgate.net

7. Quantization of Energy : Max Planck(1900) • According to Planck’s quantum theory,an atom or molecule  absorbs or emits radiation discontinuously in the form of energy packets called bundles or quanta • It successfully explained the electromagnetic spectrum distribution of black body radiation. Source : priyamstudycentre.com Presented by : pulak maity

8. Einstein photoelectric equation(1905) Source : chem.libretexts.org • Albert Einstein explained the photoelectric effect on the basis of Planck’s quantum theory. • According to this theory, light is composed of discrete particles or photos having energy hν. When a photon hits on the metal surface (sodium, potassium, zinc etc), it gives up its entire energy to the electronon the surface. Presented by : pulak maity

9. Bohr’s Shell Model (1913) • Niels Bohr expanded on Rutherford's model in the light of Planck’s Quantum Theory. • Electrons were arranged in specific energy levels or shells. • Electrons could move between energy levels by absorbing or emitting energy. • This model explained atomic spectra and stability. Source : eeeguide.com Presented by : pulak maity Success of Bohr’s Model : The Bohr model gave a picture of the hydrogen atom which was very successful, explaining all the lines in the spectrum then known.

10. Quantum Mechanical Model (1926-present) • Proposed by Schrödinger, Heisenberg, and others. • Describes the behavior of subatomic particles through quantum mechanics. • Electrons are described as wave-like particles, occupying electron clouds or orbitals. • Provides a mathematical framework for predicting an electron's probable location. Current understanding is based on the Quantum Mechanical Model. • Electrons are found in specific energy levels, sublevels, and orbitals. • Orbitals are regions of high electron density where electrons are likely to be found. • The electron configuration determines an element's chemical properties. Presented by : pulak maity Source : http://natickhighwebdesign.com/

11. Atomic orbitals : s, p, d, f • Atomic orbitals are regions of space around an atomic nucleus where electrons are most likely to be found. These orbitals describe the probability distribution of electrons and play a crucial role in understanding the electronic structure and chemical behavior of atoms. • The arrangement of electrons in these orbitals follows the Aufbau principle, Pauli exclusion principle, and Hund's rule, collectively known as the electron configuration. Understanding atomic orbitals and their electron configurations is essential for explaining the periodic trends of the elements, predicting chemical reactivity, and interpreting spectroscopic data. Presented by : pulak maity Source : researchgate

12. Conclussion • The evolution of the atomic model has revolutionized our understanding of matter. From Dalton's indivisible spheres to the modern Quantum Mechanical Model, each advancement has contributed to the development of atomic theory. These models have shaped numerous scientific fields and continue to inspire new discoveries about the building blocks of our universe. • For a visualisation of atomic orbitals , you must visit, https://www.youtube.com/watch?v=Nr40fnfHccQ Presented by : pulak maity

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