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Plato, in his dialogue Timaeus, proposed a theory of matter that shares some superficial similarities with atomism, positing that the four elements (earth, air, fire, and water) are composed of fundamental, indivisible geometric shapes, specifically right triangles and Platonic solids. -
Aristotle did not believe in atoms. He thought matter was continuous and made of four continuous elements: earth, air, fire, and water. The idea of atoms, or indivisible particles, was originally proposed by Democritus around 400 BC -
The Billiard Ball Model is the atomic theory proposed by English chemist John Dalton in the early 1800s, where atoms are envisioned as indivisible, indestructible, solid spheres similar to billiard balls. -
of Law Octaves, proposed by chemist John Newlands in 1865, stated that when elements are arranged in order of increasing atomic mass, their properties repeat every eighth element, Newlands like musical octaves. -
The photoelectric effect is the ejection of electrons, called photoelectrons, from a material when electromagnetic radiation (like light or X-rays) hits it, provided the radiation has enough energy to overcome the material's work function. -
- Radioactivity was discovered in 1896 by Henri Becquerel when he observed uranium salts emitting rays that blackened photographic plates, a phenomenon he announced to the Academy of Sciences in Paris. His groundbreaking discovery, for which he shared the 1903 Nobel Prize in Physics with Marie and Pierre Curie, paved the way for understanding the atom's structure and led to advancements in modern medicine and technology.
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The Plum Pudding Model, proposed by J.J. Thomson in 1904, is an early atomic theory that described the atom as a uniform sphere of positively charged "pudding" with negatively charged electrons, like plums, embedded within it to achieve overall electrical neutrality -
conducted by Ernest Rutherford and his team in 1911, demonstrated that atoms consist mostly of empty space with a small, dense, positively charged nucleus at their center. By firing alpha particles (positively charged) at a thin gold foil, they observed that most particles passed straight through, but a few were deflected at large angles or even bounced back. This led to the rejection of the Thomson "plum pudding" model and the establishment of the nuclear model of the atom. -
The planetary model of the atom, also known as the Bohr model, was proposed by Niels Bohr in 1913 to describe atomic structure, depicting electrons orbiting a central, positively charged nucleus in fixed, discrete energy levels or orbits, much like planets around the sun. -
The discovery of the proton is credited to Ernest Rutherford in 1920, although Eugen Goldstein provided earlier evidence of canal rays in 1886. Through his famous gold foil experiment and subsequent transmutation experiments, Rutherford identified the hydrogen nucleus as a fundamental, positively charged particle, which he named the proton. -
The neutron was discovered by British physicist James Chadwick in 1932. Building on earlier speculation by Ernest Rutherford about a neutral particle within the nucleus, Chadwick conducted experiments where he bombarded beryllium with alpha radiation, observing a neutral "ray" that behaved like a particle with a mass similar to a proton. -
The Heisenberg Uncertainty Principle is a fundamental concept in quantum physics stating that certain pairs of physical properties of a particle, such as its position and momentum, or energy and time, cannot both be known with perfect accuracy simultaneously.