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427 BCE
Plato
Plato introduced the atomic theory in which he believed that ideal geometric forms serve as atoms. According to him atoms broke down mathematically into triangles. -
400 BCE
Democritus
He promoted the idea that everything is made of atoms, indivisible and indestructible. Democritus believes that there are an infinite number of atoms, and they are always in motion always have been and always will be. The atoms move and collide, and can combine and interlock if they have compatible shapes. -
322 BCE
Aristotle
Aristotle had his own atomic theory; he believed that all matter is made of invisible particles called atoms. He believed that atoms were capable of change but only in position and motion; but not in intrinsic qualities. -
Lavoisier
Lavoisier's atomic theory model stated that in the law of conservation of mass matter was conserved during chemical changes. His experiments also brought the idea that matter was composed of chemical compounds. -
The alchemists atomic theory
The alchemists believed that all metals were formed from two principles mercury and sulfur. The mercury, gave the malleability of metals. The Sulphur, contributed body and rusting. -
John Dalton
John Dalton is know for his atomic theory; His theory suggested that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties -
Newland's Law of Octaves
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
Five years after Newland proposed his law of octaves; Mendeleev also created the famous periodic law, which states that “Element properties are a periodic function of their atomic weight.” Mendeleev placed elements in the order of their atomic weights in the form of a table known as the Periodic Table of Mendeleev. -
The Photoelectric Effect
The photoelectric effect occurs when electrically charged particles are released from a material when it absorbs electromagnetic radiation. The photoelectric effect was discovered by Heinrich Rudolf Hertz. -
Discovery of radio activity
Henri Becquerel Discovers Radioactivity. In one of the most well-known accidental discoveries in the history of physic. -
Discovery of the electron
J.J. Thomson was the scientist who discovered the electron while conducting one of his experiments; he was conducting an experiment with cathode ray tubes. The tubes showed that there were tiny negatively charged subatomic particles or electrons. As a result he proposed the plum pudding model. -
Planck's Quantum Theory
Planck's Quantum Theory states that light contains small packets of Energy called Photons which are Quantized. -
Plum Pudding
The plum pudding model (also 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” -
Rutherford's Gold foil experiment
Ruth hit a piece of gold with positively charged alpha particles; most of the particles passed straight through the gold. Clearly showing that gold atoms were made up of mostly empty space. -
Bohr's planetery model
the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. -
Robert Millikan
Robert Millikan was a physicist who discovered the charge of an electron using the oil-drop experiment. The oil-drop experiment was conducted by charging droplets of oil between two electrodes and balanced the gravitational force with the upward forces, using mechanical equilibrium to determine the charge. /**
I don't understand that very well so i couldn't use my own words to describe the experiment
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Mosley's Atomic Numbers
Mosley stated 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 protons
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. -
The Schrodinger equation
The Schrodinger equation is used to find the allowed energy levels of quantum mechanical systems (such as atoms, or transistors). -
Heisenberg uncertainty Principle
Heisenberg's uncertainty Principle states that we cannot perfectly accurately calculate the speed of particles such as protons, or electrons. The more we know their position the less we know about their speed or vice. -
Discovery of the neutron
James Chadwick stated that an atoms core also contained a new uncharged particle; he called it the neutron. He discovered this by firing alpha radiation at a beryllium sheet from a polonium source. As a result he founded the existence of the nuetron.
