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550 BCE
Aristotle's rejection
Democritus was an influential philosopher. Though, he was not as prominent than the Greek philosopher Aristotle. Aristotle disregarded Democritus’s idea of atoms. In fact, Aristotle thought the idea of atoms was absurd. Aristotle’s ideas were agreed with for more than 2000 years. -
450 BCE
Democritus Introduces the Atom
The story of the atom begins around 450 B.C. with a Greek philosopher named Democritus. Democritus wondered what would happen if you cut a piece of matter, such as a grape, into tinier and tinier pieces. He believed that a point would be reached where matter could not be cut into still smaller pieces. He called these "uncuttable" pieces atomos. This is where the modern term atom comes from. -
427 BCE
Plato
Plato introduced the atomic theory in which atoms broke down statistically into triangles, such that the structure elements had the following form: fire, air, water, earth. This was not the atomic theory fully, but rather the four-element theory. These shapes came to be known as "Platonic Solids." Plato's work was a great contribution for further development of the Atomic Theory. -
The Alchemists
The alchemists believed that all metals were formed from two principles — mercury and sulfur. The mercury, with its vital property of fluidity and fusibility, gave way to the flexibility of metals. The sulfur, with its important property of combustibleness, gave form and calcination. -
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 wrong. -
Discovery of Radioactivity
In one of the most well-known unintentional discoveries in the history of physics, on a gloomy day in March 1896, French physicist Henri Becquerel discovered spontaneous radioactivity. Which is a nuclear phenomenon. -
Law of Octaves
law of octaves, in chemistry, the generality made by the English chemist J.A.R. Newlands in 1865 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. -
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
The photoelectric effect was discovered in 1887 by the German physicist Heinrich Rudolf Hertz. Hertz observed that, when ultraviolet light shines on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking takes place. -
Discovery of the Electron
During the 1880s and ’90s scientists searched cathode rays for the mover of the electrical properties in matter. Their work ended in the discovery by English physicist J.J. Thomson of the electron in 1897. The existence of the electron showed that the 2,000-year-old conception of the atom as a homogeneous particle was wrong and that in fact the atom has a complex structure. Electron being in a negative charge. -
Quantum Theory of Light
Planck's quantum theory of 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 radiated as noticeable waves. Much hotter, and we'd start tanning from the ultraviolet light. -
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. A positive charged particle of an atom. -
Plum Pudding Model
Thomson knew that atoms had a generally neutral charge. He reasoned that there must be a source of positive charge in the atom to balance the negative charge on the electrons. -
Robert Millikan
His earliest major success was the accurate theory of the charge carried by an electron, using the falling-drop method. He also proved that this quantity was in all electrons. -
Rutherford's Gold Foil Experiment
Rutherford model describes of the structure of atoms proposed by the New Zealand-born physicist Ernest Rutherford. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is focused, around which the light, negative components, called electrons, circulate kind of like planets. -
The Bohr Model
The Bohr Model is a structural model of an atom. The model was proposed by physicist Niels Bohr in 1913. In this model, the electrons travel around the nucleus of an atom in distinct circles. -
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 says that there were three unknowns, with atomic numbers 43, 61, and 75, between aluminum and gold. -
Schrodinger Equation
It is a key result in quantum mechanics, and its discovery was a significant development. The equation is named after Erwin Schrödinger, who postulated the equation in 1925, and published it in 1926. -
Heisenberg Uncertainty Principle
Formulated by the physicist Werner Heisenberg in 1927, the uncertainty principle states that we cannot know both the position and speed of a particle with complete 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.
