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430 BCE
Democritus
Democritus was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. Democritus asserted that space, or the Void, had an equal right with reality, or being, to be considered existent. He conceived of the Void as a vacuum, an infinite space in which moved an infinite number of atoms that made up Being (i.e., the physical world. -
387 BCE
Plato
Plato was an ancient Greek philosopher born in Athens during the Classical period. In Athens, Plato founded the Academy, a philosophical school where he taught the philosophical doctrines that would later become known as Platonism. He was educated in philosophy, poetry and gymnastics by distinguished Athenian teachers including the philosopher Cratylus. -
384 BCE
Aristotle
Aristotle was an Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology and the arts. Aristotle is known for inventing the scientific method of analysis, which can be applied to multiple fields of study. -
Robert Boyle
He was best known as a natural philosopher, particularly in the field of chemistry, but his scientific work covered many areas including hydrostatics, physics, medicine, earth sciences, natural history, and alchemy. As the person who discovered that the volume of a gas decreases with increasing pressure and vice versa. -
The Alchemists
The alchemists believed that all metals were formed from two principles — mercury and sulfur. The mercury, with its essential property of fluidity and fusibility, gave rise to the malleability of metals. The sulphur, with its essential property of combustibility, contributed body and calcination. -
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 best known for introducing the atomic theory into chemistry, and for his research into colour blindness, which he had. -
Newland's Law of Octaves
When Elements are arranged in increasing order of Atomic Mass, the properties of every eighth Element starting from any Element are a repetition of the properties of the starting Element. Law of Octaves was true only for Elements up to Calcium. -
Mendeleev's Pd.Table
Mendeleev's periodic table was a good model because it could be used to predict unknown elements and their properties. All of these missing elements were eventually discovered. -
Photoelectric Effect
The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The kinetic energy of photoelectrons increases with light frequency. Electric current remains constant as light frequency increases. Electric current increases with light amplitude. -
Discovery Of Radioactivity
The discovery of radioactivity took place over several years beginning with the discovery of x-rays in 1895 by Wilhelm Conrad Roentgen and continuing with such people as Henri Becquerel and the Curie family. The application of x-rays and radioactive materials is far reaching in medicine and industry. Radioactive material is used in everything from nuclear reactors to isotope infused saline solutions. -
Planck's Quantum Theory of Light
Different atoms and molecules can emit or absorb energy in discrete quantities only. The smallest amount of energy that can be emitted or absorbed in the form of electromagnetic radiation is known as quantum. -
Plum Pudding Model
Thomson's plum pudding model of the atom, the electrons were embedded in a uniform sphere of positive charge, like blueberries stuck into a muffin. The positive matter was thought to be jelly-like, or similar to a thick soup. The electrons were considered somewhat mobile. -
Discovery of the Proton
Proved that the nucleus of the hydrogen atom (i.e. a proton) is present in the nuclei of all other atoms. -
Rutherford's Gold Foil Experiment
The Geiger–Marsden experiments were a landmark series of experiments by which scientists learned that every atom has a nucleus where all of its positive charge and most of its mass is concentrated. They deduced this after measuring how an alpha particle beam is scattered when it strikes a thin metal foil. -
Robert Millikan
Robert Andrews Millikan was born in Morrison, Illinois. He received his doctorate in physics from Columbia. He found out value of the elementary charge, which is the charge on a single electron. He measured the elementary charge using the famous oil drop experiment. -
Mosley's Atomic Numbers
Is the number of positive charges in the atomic nucleus. -
Bohr's Planetary Model
Bohr model, often referred to as a planetary model, the electrons encircle the nucleus of the atom in specific allowable paths called orbits. When the electron is in one of these orbits, its energy is fixed. -
Schrodinger Equation
The Schrödinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. Its discovery was a significant landmark in the development of quantum mechanics. -
Heisenberg Uncertainty Principle
Is a fundamental concept in quantum mechanics. It states that there is a limit to the precision with which certain pairs of physical properties, such as position and momentum, can be simultaneously known. -
Discovery of the Neutron
The essential nature of the atomic nucleus was established with the discovery of the neutron by James Chadwick in 1932 and the determination that it was a new elementary particle, distinct from the proton.