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500 BCE
Plato
Plato is most known for his "Theory of Forms". Plato's theory that suggests the physical world is not as real as the Forms. -
400 BCE
Democritus
Democritus is most famous for discovering the concept of the "atom". His theory stated that all matter is made up of tiny, indivisible particles called "atomos". These are the building blocks of everything in the universe. -
300 BCE
Aristotle
Aristotle did not make discoveries about the atom, instead, he proposed a theory where all matter was composed of four elements: earth, water, air, and fire. This theory, which is very different from modern atomic theory, prevailed for centuries. -
Robert Boyle
Robert Boyle is most commonly known for his law of gases. His law states the pressure exerted by a gas is inversely proportional to its volume when the temperature remains constant, meaning that as the volume of a gas decreases, its pressure increases, and the other way around. -
The Alchemists
Alchemists were people who practiced alchemy, the study of changing base metals into gold, creating potions of immortality, and discovering cures for disease. Alchemists experimented with metals, acids, salts, and other chemicals, and developed many nonscientific beliefs about the world. They discovered Chemical compounds like Alchemists mineral acids, alcohol, sal ammoniac, and saltpetre. They also discovered sulfuric acid. -
John Dalton
John Dalton was an English chemist, physicist, and meteorologist, best known for introducing the atomic theory into chemistry and for his work on human optics. He is recognized for his discovery of the "atomic theory," which proposed that all matter is made up of tiny, indivisible particles called atoms, with different elements having distinct types of atoms with unique properties. -
Newland's Law of Octaves
According to the Newland's law of octaves, when elements are arranged in the order of increasing atomic masses, the properties of the eight elements (starting from a given element) are a repetition of the properties of the first element. This law was discovered by John Newlands. -
Mendeleev's Pd. Table
Dmitri Mendeleev, Russian chemist and inventor, invented the Mendeleev Pd. Table. Mendeleev had a dream, and when he woke up, Mendeleev drew the table he had envisioned. While arranging these cards of atomic data, Mendeleev discovered what is called the Periodic Law. Mendeleev arranged the elements in order of increasing relative atomic mass. -
Photoelectric Effect
Heinrich Rudolf Hertz discovered that when light shines on a metal, electrons can be ejected from the surface of the metal. -
Discovery of Radioactivity
Henri Becquerel discovered radioactivity in 1896. When he investigated the newly discovered X-rays in 1896, it led to studies of how uranium salts are affected by light. By accident, he discovered that uranium salts randomly emit a radiation that can be registered on a photographic plate. -
Phanck's Quantum Theory of Light
Planck's Quantum Theory of Light states that light is not emitted or absorbed as a continuous wave, but rather in discrete packets of energy called "quanta" or "photons." This means that light behaves like particles with specific energy levels directly proportional to their frequency. Planck's theory helped establish the concept of wave-particle duality, where light can behave as both a wave and a particle depending on the experiment. -
Plum Pudding Model
The plum pudding model was the first scientific model of the atom to describe an internal structure. J.J. Tompson was the first to propose this model. Tompson stated that the atom looked like a plum pudding close plum pudding model. -
Robert Millikan
Robert was credited with the discovering the value for electron charge, through the well-known oil drop experiment. He is also known for his achievements related to the photoelectric effect and cosmic radiation. -
Rutherford's Gold Foil Experiment
Ernest Rutherford discovered piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. Rutherford showed that the gold atoms were mostly empty space. -
Bohr's Planetary Model
According to the Bohr model, the electrons circle the nucleus of the atom in specific paths called orbits. When the electron is in one of these orbits, its energy is fixed. -
Mosley's Atomic Numbers
Mosley's Atomic Numbers is the concept that the atomic number of an element is the number of positive charges in its nucleus. Henry Mosley established that the atomic number, not atomic mass, is the fundamental property of an element. -
Discovery of the Proton
Ernest Rutherford is credited with the discovery of the proton. He identified the hydrogen nucleus as a fundamental particle and named it a "proton" based on the Greek word "protos" meaning "first.". -
Schrodinger Equation
The Schrödinger equation is a mathematical formula in quantum mechanics that describes how the "wave function" of a particle change over time. This acted as a prediction of where a tiny particle like an electron might be found, rather than giving a precise location, because at the quantum level particles behave like waves, not solid objects -
Heisenberg Uncertainty Principle
German physicist Werner Heisenberg discovered that the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory. -
Discovery of the Neutron
In May of 1932, James Chadwick discovered the neutron. A schematic diagram of the experiment used to discover the neutron. The experiment led by Chadwick involved experiments where alpha particles were fired at beryllium, producing a previously unknown radiation that was later determined to be neutrons