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500 BCE
The alchemists 500Bc - 1720
Alchemists were the first to use the word element in reference to chemicals, they also analyzed matter and its form in a chemical reaction. -
475 BCE
Plato 475Bc
Plato was an ancient Greek philosopher known for his Theory of Forms. He believed that beyond our physical world, there are perfect, abstract ideas or forms. For example, many different chairs in the world share the essence of "chair-ness" in this realm. He stressed the importance of reason and philosophy in understanding truth and knowledge. -
460 BCE
Democritus 460-490Bc
He made his atomic theory that the atom was just one sphere -
320 BCE
Aristotle 320Bc
Aristotle concluded that everything is composed of four elements -
Robert Boyle 1660
Robert Boyle discovered that the volume of a gas decreases with increasing pressure and vice versa—the famous Boyle's law. -
Jhon Dalton 1803
John Dalton was a scientist who said that everything is made of tiny parts called atoms. Each type of atom is different, and they join together to make new things. His ideas helped us understand chemistry better! -
New lands law of octaves 1865
The law of octaves is 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 1869
Dmitri Mendeleev created the periodic table in 1869 by arranging elements by atomic mass and grouping similar properties. His table revealed patterns and helped predict undiscovered elements, forming the basis for the modern periodic table. -
Discovery of radioactivity
Henri Becquerel saw that uranium salts emitted a radiation that could be detected on photographic plates, even on cloudy days when the salts weren't exposed to sunlight. -
Planck's Quantum Theory of light 1900
Planck's quantum theory, developed by Max Planck in 1900, states that light is emitted in discrete packets of energy called "quanta" or "photons." It introduced the concept of quantized energy levels, laying the foundation for quantum mechanics and explaining phenomena like blackbody radiation and the photoelectric effect. -
Plum pudding model 1904
The plum pudding model represents the electrons as negatively-charged particles embedded in positive charge. -
Photoelectric effect 1905
The photoelectric effect is when light hits something and makes it spit out tiny particles called electrons. If the light is strong enough, it can knock the electrons out. This shows that light can act like both a wave and a particle, which helped scientists learn more about how things work at a tiny level. Albert Einstein explained it a long time ago. -
Robert Millikan 1910
Robert Millikan was an American physicist known for his oil drop experiment, which measured the charge of the electron. Conducted in the early 1900s, this experiment confirmed the existence of discrete electric charge and provided a precise value for the electron's charge, enhancing our understanding of atomic structure. -
Rutherford's gold foil experiment 1911
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 has mostly empty space -
Bohr's planetary model
Bohr's planetary model consisted of the electrons encircle the nucleus of the atom in specific allowable paths called orbits. -
Mosley's atomic number 1913
Henry Moseley was a British physicist who, in 1913, established atomic numbers, showing that elements should be arranged by the number of protons instead of atomic mass. This improved the periodic table and clarified the relationships between elements. -
Discovery of the proton 1917
Ernest Rutheford proved that the nucleus of the hydrogen atom (i.e. a proton) is present in the nuclei of all other atoms. -
Schrodinger equation 1926
The Schrödinger equation is a fundamental equation in quantum mechanics that describes how a system's quantum state changes over time. Formulated by Erwin Schrödinger in 1925, it uses wave functions to represent particles' behavior and is essential for understanding atomic and molecular properties. -
Heisenberg uncertainty principle 1927
Heisenberg uncertainty principle consisted of the position and the velocity of an object cannot both be measured exactly, at the same time, even in theory. -
Discovery of the neutron 1932
James Chadwick discovered neutrons by firing alpha particles at beryllium, which produced radiation. When this radiation hit wax, it knocked out protons. Chadwick realized the radiation was made of uncharged particles similar in weight to protons, which he called neutrons. This was key to understanding atoms!