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427 BCE
Plato
In 427 B.C.E. Plato introduced the atomic theory in which ideal geometric forms serve as atoms, according to which atoms broke down mathematically into triangles. -
400 BCE
Democritus
Democritus, a Greek philosopher, was known in antiquity as the 'laughing philosopher' because of his emphasis on the value of 'cheerfulness,' was one of the two founders of ancient atomist theory. His theory was that all material bodies are made up of indivisibly small “atoms.” -
335 BCE
Aristotle
In his metaphysics, he claims that there must be a separate and unchanging being that is the source of all other beings. In his ethics, he holds that it is only by becoming excellent that one could achieve eudaimonia, a sort of happiness or blessedness that constitutes the best kind of human life -
Lavoisier
Antoine Lavoisier was a French chemist he was know as "the father of modern chemistry". He discovered the role of oxygen in combustion and respiration, and he proved the law of conservation, Also he reformed the chemical nomenclature and lastly he named hydrogen. -
The Alchemists
In 1803 the alchemists believed that all metals were formed from two principles — mercury and sulfur. Alchemy Contributed to the Atomic Theory, by laying down the foundation of the Modern Day Periodic Table of the elements. -
John Dalton
John Daltons theory was that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties. This was created in 1808 -
Newlands law of octaves
The English chemist, J.A.R. Newland created the law of octaves. The law said that 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. He attempted to combine the 62 elements known at the time. He arranged them in ascending order according to their atomic weights and discovered that the properties of every eighth element were the same. -
Mendeleev's PD. Table
Dmitri Mendeleev devised the periodic classification of the chemical elements. Mendeleev claimed the famous periodic law that “Element properties are a periodic function of their atomic weight.” -
Photoelectric Effect
The photoelectric effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz. The Photoelectric effect is phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation. -
Discovery of radioactivity
In 1896 Henri Becquerel discovered radio activity. He discovered radioactivity on accident. He was starting from a wrong idea progressively realized what he was observing, he was regularly informing the French Academy of Sciences of the progress he was doing. -
Discovery of the electron
English physic J.J. Thomson discovery the electron. He was experimenting with cathode ray tubes. He first proved of negatively charged particles within and atom called electrons. -
Plum Pudding Model
J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. 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. -
Planck's Quantum Theory of Light
In 1905 the theory was created. This was created by Niels Bohr and Max Planck. The theory of light says 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. Also different atoms and molecules can emit or absorb energy in discrete quantities only. -
Rutherford's Gold Foil Experiment
Ernest Rutherford did the gold foil experiment in 1911. A piece of gold foil was hit with alpha particles, which have a positive charge. When most of the alpha particles went through it showed that the gold atoms were mostly empty space. -
Bohrs planetary model
In 1913 Ruthford Bohr made a planetary model. The model showed the electrons encircle the nucleus of the atom in specific allowable paths called orbits. -
Robert Millikan
Robert Andrews Millikan was an American physicist. He discovered the elementary charge of an electron using the oil-drop experiment. This discovery was made in 1913. He elegantly measured the fundamental unit of electric charge. -
Moseley's Atomic Numbers
In 1914 Henry Moseley a English physicist published a paper in which he concluded that the atomic number is the number of positive charges in the atomic nucleus. He also stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. He discovered a systematic relation between wave- length and atomic number. -
Discovery of the Proton
In 1920 Ernest Rutherford discovered the proton. During his research it led to a nuclear reaction which led to the first 'splitting' of the atom. That is when he first discovered the Proton. -
Charge of the electron
Robert Millikan discovered charge of electron and won Noble prize in physics in 1923. It carries a negative charge of 1.602176634 × 10−19 coulomb, which is considered the basic unit of electric charge -
Heisenberg Uncertainty Principle
Werner Heisenberg a German physicist and Nobel laureate formulated the Heisenberg Uncertainty principle 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 the Neutron
James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron in 1932. Chadwick was convinced that alpha particles did not have enough energy to produce such powerful gamma-rays. He performed the beryllium bombardment experiments himself and interpreted that radiation as being composed of particles of mass approximately equal to that of the proton but without electrical charge, neutrons. -
Schrodinger Equation
In 1962 the Schrodinger equation was created by Erwin Schrodinger. The Schrodinger equation is a linear partial differential equation that governs the wave function of a quantum-mechanical system.