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440 BCE
Plato
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 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. -
332 BCE
Aristole
In Aristotle's time, atomists held that matter was fundamentally constructed out of atoms. These atoms were indivisible and uniform, of various sizes and shapes, and capable only of change in respect of position and motion, but not intrinsic qualities. -
Lavoisier
Lavoisier believed that matter was neither created nor destroyed in chemical reactions, and in his experiments he sought to demonstrate that this belief was not violated. -
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 (rusting). -
John Dalton
Dalton's theory was based on the concept that each element consists of its own unique brand of indivisible atom. atoms of one element are all alike but they differ from atoms of other elements. Importantly, Dalton assigned atomic weights to the atoms of the 20 elements he knew of at the time. This was back in 1808 -
Newlands Law of Octaves
back in 1865, the law of octaves was made by Isaac Newton himself. The law linked certain elements properties to their Atomic Masses and basically arranged them into categories. -
Mendeleevs Pd. Table
Dmitri Mendeleev devised the periodic classification of the chemical elements, in which the elements were arranged in order of increasing atomic weight. -
Photoelectric effect
The photoelectric effect is a phenomenon where electrons are emitted from the metal surface when light of sufficient frequency is incident upon it. The concept of the photoelectric effect was first documented in 1887 by Heinrich Hertz and later by Lenard in 1902. -
Discovery of radioactivity
Henri Becquerel Discovered 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. -
Charge of the electron
J. J. Thomson discovered the electron in 1897 when he measured the charge-to-mass ratio for electrons in a beam. -
Discovery of the electron
Joseph John Thompson discovered the electron. He described his experiments with cathode rays to verify the existence of these subatomic corpuscles. -
Discovery of the proton
Ernest Rutherford discovered the proton back the early 1990s and he did so through an experiment that caused a chemical and nuclear reaction and it split the atom and he named a certain part protons. -
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 (also known as Thomson's plum pudding model) is a historical scientific models 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
what happened was 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. -
Robert Millikan
His earliest major success was the accurate determination of the charge carried by an electron. He also proved that this quantity was a constant for all electrons, thus demonstrating the atomic structure of electricity. -
Bohr's planetary model
in the year 1913, Niels Bohr had a theory for the hydrogen atom. He believed that in the atom there was a structure of orbits around the nucleus and on those orbits are electrons. -
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 stated that there were three unknown elements, with atomic numbers 43, 61, and 75, between aluminum and gold. -
Schrodinger 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 the neutron
In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron. Also, The discovery of neutrons can be traced back to the year 1930 when the German nuclear physicists Herbert Becker and Walther Bothe observed that a penetrating form of radiation was produced when the alpha particles emitted by polonium was incident on relatively light elements such as lithium, beryllium, and boron.