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430 BCE
Democritus atomic model
Democritus believed that atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped. Differences in atomic shape and size determined the various properties of matter. -
427 BCE
Plato contribution to atom
Plato introduced the atomic theory in which ideal geometric forms serve as atoms, -
384 BCE
aristotle contribution to atom
Aristotle did not believe in the atomic theory and he taught so otherwise. He thought that all materials on Earth were not made of atoms, but of the four elements, Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements of matter. -
lavoisier contribution
Antoine Lavoisier, a French chemist, mainly discovered the role of oxygen in combustion and respiration, proved the law of conservation, reformed the chemical nomenclature, and named hydrogen. -
John dalton
John Dalton (1766-1844) was an English chemist, physicist, and meteorologist, best known for introducing the atomic theory into chemistry and for his work on human optics. -
mendeleev 's pd table
In 1869, Russian chemist Dmitri Mendeleev created the framework that became the modern periodic table, leaving gaps for elements that were yet to be discovered. While arranging the elements according to their atomic weight, if he found that they did not fit into the group he would rearrange them. -
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
scientists searched 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. -
charge of the elctron
electron, lightest stable subatomic particle known. It carries a negative charge of 1.602176634 × 10−19 coulomb, which is considered the basic unit of electric charge. The rest mass of the electron is 9.1093837015 × 10−31 kg, which is only 1/1,836the mass of a proton. -
planck's quantum theory of light
Specifically, Planck's quantum theory of fussy light tells us that light bulb filaments should be heated to a temperature of about 3,200 Kelvin to ensure that most of the energy is emitted as visible waves. Much hotter, and we'd start tanning from the ultraviolet light. -
Plum Pudding Model
The plum pudding model known as Thomson's 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”. -
robert milikan
His earliest major success was the accurate determination of the charge carried by an electron, using the elegant “falling-drop method”; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity. -
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. -
Borh's planetary model
the electrons encircle the nucleus of the atom in specific allowable paths called orbits. -
mosley's atomic number
Moseley published a paper in which he concluded that the atomic number is the number of positive charges in the atomic nucleus. -
Discovery of the proton
The proton was discovered by Ernest Rutherford in the early 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. -
Schrödinger 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
The British physicist Sir James Chadwick discovered neutrons in the year 1932. He was awarded the Nobel Prize in Physics in the year 1935 for this discovery. It is important to note that the neutron was first theorized by Ernest Rutherford in the year 1920. -
New lands law of octaves
if the chemical elements are arranged according to increasing atomic weight, those with similar physical and chemical properties occur after each interval of seven elements. -
the alchemist contributions atomic theory
By Breaking down the chemical composition of the 4 basic elements of its period, Fire, Earth, Wind, And water eventually evolved into The Periodic table we use today. Alchemy Contributed to the Atomic Theory, by laying down the foundation of the Modern Day Periodic Table of the elements.