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460 BCE
Democritus
Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped -
427 BCE
Plato
Plato introduced the atomic theory in which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles -
348 BCE
Aristotle
2.1 Atomism in Aristotle and Boyle. In Aristotle's time, atomists held that matter was fundamentally constructed out of atoms -
1000
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 sulfur, with its essential property of combustibility, contributed body and calcination (rusting). -
Lavoisier
In June 1783, Lavoisier reacted oxygen with inflammable air, obtaining "water in a very pure state." He correctly concluded that water was not an element but a compound of oxygen and inflammable air, or hydrogen as it is now known. To support his claim, Lavoisier decomposed water into oxygen and inflammable air. -
John Dalton
Dalton's atomic theory said that all matter was made of indivisible and indestructible atoms with distinct masses and properties the combination of which determined the physical nature of their constituent elements. -
Newlands Law of Octaves
Newland's Law of Octaves says that when elements are put 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 -
Mendeleevs Pd Table
Mendeleev realized that the physical and chemical properties of elements were related to their atomic mass in a periodic way, and put them so that groups of elements with similar properties fell into vertical columns in his table. -
Photoelectric Effect
photoelectric effect, phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. The effect is often defined as the ejection of electrons from a metal plate when light falls on it. -
Discovery of Radioactivity
Henri Becquerel Discovers Radioactivity. In one of the most well-known accidental discoveries in the history of physics, on an overcast day in March 1896, French physicist Henri Becquerel opened a drawer and discovered spontaneous radioactivity. -
Discovery of the Electron
During the 1880s scientists looked at cathode rays for the carrier of the electrical properties in matter. Their work culminated in the discovery by English physicist J.J. Thomson of the electron in 1897. -
Plancks Quantum Theory
According to Planck's quantum theory, 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
The plum pudding model is a historical scientific model of the atom. The plum pudding model is defined by electrons surrounded by a volume of positive charge, like negatively-charged plums embedded in a positively-charged pudding -
Rutherfords Gold Foil Experiment
A piece of gold foil was hit with alpha particles, which have a positive charge. Most alpha particles went right through. This showed that the gold atoms were mostly empty space. -
Bohrs Planetary Model
The electrons surround the nucleus in specific paths called orbits. When the electron is in one of these orbits, its energy is fixed. -
Robert Milikan
During the 1890s the theory that electricity was conveyed by a miniscule unit, the electron Millikan succeeded in precisely determining the magnitude of the electron’s charge. Small electrically charged drops of oil were suspended between two metal plates where they were subjected to the downward force of gravity and the upward attraction of an electrical field. By measuring how the various drops of oil moved about -
Mosleys Atomic Numbers
In 1914 Moseley published a paper in which he concluded that the atomic number is the number of positive charges in the atomic nucleus. He also said that there were three unknown elements, with atomic numbers 43 61 and 75 between aluminum and gold -
Discovery of the Proton
protons were discovered by Ernest Rutherford in the 1900's. During this period, his research resulted in a nuclear reaction which led to the first 'splitting' of the atom, where he discovered protons. He named his discovery “protons” based on the Greek word “protos”. -
Charge of the Electron
. It carries a negative charge of 1.602176634 × 10−19 coulomb, which is considered the basic unit of electric charge. -
Schroding Equation
The Schrödinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system. It is a key result in quantum mechanics, and its discovery was a significant landmark in the development of the subject. -
Heisenberg Uncertainty Principle
Formulated by the German physicist and Nobel laureate Werner Heisenberg in 1927, the uncertainty principle states that we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy -
Discovery of Neutron
In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron. Chadwick was born in1891 in Manchester, England.