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300
Democritus
In 400 B.C., Democritus was the first person to come up with the concept of a piece of matter that was indivisible into smaller parts. He called these indivisible parts "atoma" , which is where we get our word "atom" -
Period: 300 to
Year
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Antoine Lavoisier
Antoine Lavoisier, often referred to by many as the father of modern chemistry, was a French chemist who is notable for numerous findings, including discovering that even though matter might change its shape or form, its mass will always remain the same. -
Law of Conservation of Mass
The law of conservation of mass was first clearly formulated by Lavoisier in 1789, who is often for this reason referred to as a father of modern chemistry. However, Mikhail Lomonosov had previously expressed similar ideas in 1748 and proved them in experiments. Others who anticipated the work of Lavoisier include Joseph Black, Henry Cavendish, and Jean Rey. -
John Dalton
Dalton’s atomic model is one of the fundamentals of physics and chemistry. He discovered that certain gases only could be combined in certain proportions even if two different compounds shared the same common element or group of elements. -
Dalton's Atomic Theory
First, Pure Elements consist of particles called atoms. Second,atoms of an element are all the same for that element. That means gold is gold and oxygen is oxygen down to the last atom. Third, atoms of different elements can be told apart by their atomic weights. Fourth, atoms of elements unite to form chemical compounds. Finally, atoms can neither be created or destroyed in chemical reaction. -
Dmitri Mendeleev
Dmitri Mendeleev discovered qualities of new elements, which were missing from the periodic table, that he had accurately predicted would exist, namely germanium, gallium and scandium. He is also credited for creating the first version of the Periodic Table of Elements and introducing the metric system to the Russian Empire. He wrote a text book in the late 1860s, called 'The Principles of Chemistry', which paved the way for modern theories in chemistry and physics. -
Cathode Ray Tube
The first cathode ray tube scanning device was invented by the German scientist Karl Ferdinand Braun in 1897. Braun introduced a CRT with a fluorescent screen, known as the cathode ray oscilloscope. The screen would emit a visible light when struck by a beam of electrons. -
JJ Thompson
Thomson's discovery of the electron began in 1895 with a series of experiments in the Cavendish Laboratory. Thomson might be described as "the man who first split the atom," and to a great extent, he made atom physics a modern science. -
Plum Pudding Atomic Model
The Plum Pudding Model is an atom model proposed by JJ Thomson, the physicist who discovered the electron. It is also known as the Chocolate Chip Cookie or Blueberry Muffin Model. -
Robert Millikan
American physicist honoured with the Nobel Prize for Physics in 1923 for his study of the elementary electronic charge and the photoelectric effect. In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron.He obtained more precise results in 1910 with his famous oil-drop experiment in which he replaced water with oil. -
Rutherford Model
The Rutherford model is a model of the atom devised by Ernest Rutherford. Rutherford's new model[1] for the atom, based on the experimental results, contained the new features of a relatively high central charge. This region would be named the "nucleus" of the atom in later years. -
Henry Moseley
Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous chemical concept of the atomic number. This spread his development of Moseley's law in X-ray spectra. Moseley's Law justified many concepts in chemistry by sorting the chemical elements of the periodic table of the elements in order based on the physics if the element. -
Niels Bohr
A Danish physicist who made foundational understanding to atomic structure and quantum theory. Developed the Bohr model of the atom, in which he stated that energy levels of electrons are little, and they revolve in stable orbits around the atomic nucleus, like planets around the sun, except they can jump from one energy level (or orbit) to another -
Bohr Planetary
The Bohr Model is a planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically related to the electric force between the positively-charged nucleus and the negatively-charged electrons). -
Gold Foil Experiment
Before Ernest Rutherford's landmark experiment with a few pieces of metal foil and alpha particles, the structure of the atom was thought to correspond with the plum pudding model. The faulty aspect of this model is that it was construed before the nucleus of an atom and its composition was discovered; which is where Rutherford's research comes in. -
Erwin Schrodinger
Austrian physicist who developed a number of fundamental results in the field of quantum theory, which formed the basis of wave mechanics. -
Quantum Mechanical Model
The quantum mechanical model is based on mathematics. The quantum mechanical model of the atom uses complex shapes of orbitals or oval orbits. The principal quantum number n describes the average distance of the orbital from the nucleus and the energy of the electron in an atom. -
Ernest Rutherford
In 1911, although he could not prove that it was positive or negative, he theorized that atoms have their charge concentrated in a very small nucleus. He pioneered the Rutherford model of the atom, through his discovery of Rutherford scattering in his gold foil experiment. He is highly credited with first "splitting the atom" in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered and named the proton. -
James Chadwick
An English physicist who was awarded the 1935 Nobel Prize in physics for his discovery of the neutron in 1932. He was knighted in 1945 for achievements in physics. During the Second World War, he carried out research as part of the Tube Alloys project to build an atomic bomb. -
Electron Cloud Model
The electron cloud model is an atom model where the electrons are no longer depicted as particles moving around the nucleus in a fixed orbit. Instead, as a quantum mechanically-influenced model, we shouldn’t know exactly where they are, and we can't describe their possible location around the nucleus.
