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400 BCE
Democritus and Matter
Democritus was an ancient Greek philosopher who proposed that all matter is made up of tiny, indivisible particles called "atomos," meaning "uncuttable." He believed that these atoms differed in shape, size, and motion, which determined the properties of different materials. Unlike later scientists, he had no experimental proof but relied on logical reasoning. Democritus' atomic theory laid the foundation for modern atomic science. -
300 BCE
Aristotle and matter
Aristotle rejected Democritus' idea of atoms and instead proposed that all matter is made up of four fundamental elements: earth, water, air, and fire. He believed that these elements combined in different ways to form all substances and that matter was continuous rather than made of tiny, indivisible particles. Aristotle’s ideas were widely accepted for centuries, influencing scientific thought until the development of modern atomic theory. -
Dalton and Solid Sphere
In the early 1800s, atomic theory was largely shaped by John Dalton. He proposed that all matter is made of indivisible, solid spheres called atoms. Each element had its own unique type of atom, and chemical reactions involved the rearrangement of these atoms in fixed ratios to form compounds. Dalton’s theory helped explain the conservation of mass and definite proportions in chemical reactions. While later discoveries showed that atoms have internal structures. -
Dalton and Atomic Theory
John Dalton introduced his atomic theory, which proposed that all matter is made of tiny, indivisible atoms. He stated that each element has its own unique atoms, which differ in mass and properties from those of other elements. Dalton also explained that atoms combine in simple, whole-number ratios to form compounds and that chemical reactions involve the rearrangement of atoms without their creation or destruction. His work laid the foundation for modern atomic science -
J.J Thomson and Electrons
J.J. Thomson made a groundbreaking discovery in atomic theory by identifying the electron, proving that atoms are not indivisible as previously thought. Using a cathode ray tube, he demonstrated that atoms contain tiny, negatively charged particles. This led to the "plum pudding" model, where electrons were embedded in a positively charged sphere. -
Einstein
Albert Einstein contributed to atomic theory in 1905 by explaining Brownian motion, providing evidence that atoms exist. His E = mc² equation showed that mass and energy are interchangeable, laying the foundation for understanding nuclear reactions. His work influenced the development of quantum mechanics and later atomic models, even though he disagreed with some quantum principles, like Heisenberg’s Uncertainty Principle. -
Rutherford and Gold Foil
Ernest Rutherford conducted experiments that led to a major breakthrough in atomic theory. Through his gold foil experiment (completed in 1909 and published in 1911), he discovered that atoms have a small, dense, positively charged nucleus. This challenged J.J. Thomson’s "plum pudding" model and led to the nuclear model of the atom, where electrons orbit around the nucleus. -
Bohr and his atomic model
In 1913, Niels Bohr introduced a new atomic model that improved upon previous theories. He proposed that electrons orbit the nucleus in fixed energy levels or shells, rather than moving randomly. Bohr's model explained why atoms emit light at specific wavelengths, supporting the idea of quantized energy levels. His work built on Rutherford’s discovery of the nucleus and helped develop quantum mechanics, shaping our modern understanding of atomic structure. -
Period: to
Heisenberg, Chadwick, And Schrodinger
Heisenberg’s Uncertainty Principle showed that the exact position and momentum of an electron cannot be known simultaneously. Schrödinger further refined this with his wave equation, describing electrons as existing in regions of probability rather than fixed orbits. Chadwick’s discovery of the neutron helped complete the atomic model by explaining atomic mass and the structure of the nucleus. Their work led to the modern quantum mechanical model of the atom. -
Electron Cloud Model
The Electron Cloud Model describes electrons as existing in probability clouds rather than fixed orbits. Erwin Schrödinger (1926) used wave equations to predict electron locations, while Werner Heisenberg (1927) introduced the Uncertainty Principle, stating an electron's exact position and momentum cannot be known simultaneously. This quantum mechanical model replaced earlier atomic theories and better explains electron behavior and interactions. -
Heisenberg, Chadwick, Einstein Schrodinger
same as before -
Expanding through the 2000's
By the 2000s, atomic theory had advanced with quantum mechanics and the Standard Model, explaining subatomic particles like quarks and gluons. Particle accelerators, such as the Large Hadron Collider, helped confirm theories, leading to discoveries like the Higgs boson in 2012. Research focused on refining atomic models, nuclear physics, and applications in nanotechnology and quantum computing, pushing the boundaries of modern science. -