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500 BCE
The Alchemists
Alchemists were people who developed basic knowledge about matter as well as the hidden nature and transformations.
They broke down the chemical composition of the 4 basic elements of the period such as Fire, Earth, Wind, And water which soon turned into the The Periodic table we use in todays time. They came up with an atomic theory that has 5 steps. -
427 BCE
Plato
Plato founded the atomic theory in which geometric forms serve as atoms, atoms break down mathematically into different shapes that resembled different form of elements in shapes such as fire is a tetrahedron, air is a octahedron, water is a icosahedron and earth is a cube. -
400 BCE
Democritus
Democritus claimed that matter was made of small, hard particles that he called atoms. He also discovered matter could not be separated into smaller particles forever. -
330 BCE
Aristole
Aristole believed that all materials were not made of atoms, he believed all materials on earth such as fire, wind, air and water were made of all substances. His theory was that a mass of unclear size was everywhere and there was no separate particles for each material and that it was all one. -
Lavoisier
Antoine Lavoisier was a French chemist who was known a the "father of modern chemistry" who discovered the role of oxygen in respiration and combustion. He named oxygen and hydrogen and established the Law of conservation of mass. -
John Dalton
John Dalton was an English chemist, meteorologist an physicist who was the first person to ever explain that everything that exists is made up of atoms and atoms are indestructible an identical in mass and properties. -
New Land of Octaves
John Newland founded the New land of Octaves which states that when Elements are arranged in an increasing order of Atomic Mass, the properties of every eighth Element beginning from any Element are a repeating pattern of the properties of the starting Element. Which basically means its a on going pattern of the periodic table. -
Mendeleev's Pd. Table
Dmitri Mendeleev came up with the Mendeleev periodic table. Five years after John Newlands discovered his Law of Octaves. Dmitri Mendeleev came up with a periodic table and also arranged the elements in order of relative atomic mass. -
Photoelectric effect
Heinrich Rudolf Hertz founded the photoelectric affect in 1887. Heinrich observed that when ultraviolet light shines on two metal electrodes with a voltage applied across them, the light changes the voltage at which sparking happens. -
Discovery of Radioactivity
Antoine Henri Becquerel was the one to discover radioactivity. In 1869 he was investi8gating uranium salts while he accidentally discovered radioactivity. He found that photographic plates were fully exposed when in reach of radioactive salt. -
Charge of the Electron
Robert Millikan was the one who founded electrons by the oil droplet test but also discovered what the charge of an electron would be. He determined the charge of an electron by using the smallest droplet possible of oil, by doing this he determined the charge of an electron was because it wasn't possible to find a lower charge. -
Discovery of the electron
John Thomson was the one to discover electrons in 1897. He discovered electrons by doing an experiment using a cathode ray tube. He then created a model which was called the plum pudding model to tell the difference between positive and negative parts of an atom. -
Planck's Quantum Theory
Max Planck created Planck's Quantum theory which is a theory of black body radiation which is when an object absorbs and release it's radiation. This means different molecules and atoms can release or absorb energy in separate amounts only. The smallest amount of energy that can be released or absorbed is known as quantum. -
Plum Pudding Model
J.J Tompson created the plum pudding model is a model of the atom. The plum pudding model is explained by electrons surrounded by a volume of positive charge. -
Rutherford's Gold Foil Expeirment
Ernest Rutherford figured out the structure of the atom and fired alpha particles on a super thin piece of gold foil. The discovered that particles were deflected through large angles and could be reflected back directly from that source. This shows the atoms are mostly made up of empty space. -
Robert Millikan
Robert Millikan was an American physicist and measured the charge of an electron by using oil droplets. He discovered the charge and mass that is carried by an electron. -
Bohr's planetary Model
Neils Bohr founded the planetary model which is a model where the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. The model is also referred to as the planetary model of an atom. The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons. -
Mosley's Atomic Numbers
In 1914 Henry Mosley published a paper in which he determined that the atomic number is the number of positive charges in an atoms nucleus. While at the University of Manchester, he observed the X-ray spectra of various chemical elements using diffraction in crystals. Through this process, he discovered a similar relation between wave- length and atomic number. This observation is n ow known as Mosleys Law. -
Discovery of the proton
Ernest Rutherford discovered the discovery of the proton by doing research which ended in a nuclear reaction which led to the first atom splitting in half which helped him discover protons. -
Schrodinger Equation
Erwin Schrodinger discovered the Schrodinger equation. This is an equation of motion that works for very small microscope particles of quantum chemistry. This equation is used to solve problems on the atomic structure of matter. -
Heisenberg uncertainty principle
Warner Heisenberg created the Heisenberg uncertainty principle of a quantum theory. According to this principle, ” Position and momentum of an electron cannot be determined simultaneously with absolute accuracy.” This principle means you can either know how fast it is going, or where it's located, but not both at the same time without being not sure. -
Discovery of the neutron
James Chadwick announced that the core of an atom also contained a new not charged particle, which he named it a neutron in 1932.
