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428 BCE
plato
Plato was a Greek philosopher born in Athens during the Classical period in Ancient Greece. He founded the Platonist school of thought and the Academy, the first institution of higher learning on the European continent. -
400 BCE
Democritus
He theorized that all material bodies are made up of indivisibly small “atoms.” -
384 BCE
aristotle
Aristotle was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of philosophy within the Lyceum and the wider Aristotelian tradition. -
lavoisier
Lavoisier found that mass is conserved in a chemical reaction. The total mass of the products of a chemical reaction is always the same as the total mass of the starting materials consumed in the reaction. -
john dalton
Dalton proposed that every single atom of an element, such as gold, is the same as every other atom of that element. -
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). -
newland's law of octaves
John Newlands found that 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. -
mendeleev's pd. table
One of the unique aspects of Mendeleev's table was the gaps he left. In these places he not only predicted there were as-yet-undiscovered elements, but he predicted their atomic weights and their characteristics. -
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 and '90s 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. -
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 is defined by electrons surrounded by a volume of positive charge, like negatively-charged “plums” embedded in a positively-charged “pudding” (hence the name). -
rutherford's 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. -
robert millikan
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. -
bohr's planetary model
the electrons encircle the nucleus of the atom in specific allowable paths called orbits -
mosley's 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. -
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. He named his discovery “protons” based on the Greek word “protos” which means first. -
charge of the electron
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. -
the 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
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.