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An Atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The Atom was theorized by a man named Democritus of Abdera, Thrace in between c. a 460 BC – ca. 370 B. C. Atom is derived from the Greek word “atomos” , which means to be uncuttable. He had a theory that everything is composed of “atoms”, which he believed that these minuscule objects are indivisible, indestructible and have and always been in motion, had a void that exists between atoms, they are solid, homogeneous, and differ in size, shape, mass, position, arrangement, etc.
Democritus identified all of these qualities by using the analogies from our sense experiences. In the early 1800 John Dalton, a meteorologist/ color blindness physician, came up with his own atomic theory and The Dalton Model. Even though, the idea of atoms were already proposed by Democritus, his theory was different in that it had the weight of careful measurements behind it. John Dalton’s Atomic Theory consisted of these facts: All elements are composed of tiny indivisible particles called atoms. Atoms of the same elements are identical. The atoms of any one element are different from those of any other element.
Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are ever changed into atoms of another element as a result of a chemical reaction. Important changes were revised from his theory like his atoms are indivisible which is wrong since atoms can be divided into subatomic particles like Protons,Neutrons, and Electrons. Next, is his theory that Atoms of all elements are the same, this is proven wrong by the discovery of isotopes.
Lastly, his theory that elements can’t be transformed into other elements, which is also proven wrong because elements can be changed into other elements through radioactivity. About less than 100 years later after John Dalton’s findings, in 1897 Sir Joseph John “J. J. ” Thomson, OM, FRS of Great Britain received the 1906 Nobel Prize in Physics for his discovery of the electron and for The Thomson’s atomic model. He assumed that the body of an atom is a spherical object containing N electrons confined in homogeneous jellylike but relatively massive positive charge distribution whose total charge cancels that of the N electrons.
It was sometimes nicknamed as plum pudding model, because of its features as you can see below. Next great physicist that would step up to the plate and take over world of Atoms, was The 1st Baron Rutherford of Nelson, also known as Ernest Rutherford OM, FRS. He was also awarded with a Nobel Prize in Chemistry in 1908, just like Thomson did a couple decades ago, for his investigations of the elements and discovery of the chemistry of radioactive substances. He proposed a model in which the electric charge +Ze in an atom is not distributed over the whole area of the atom but concentrates in a small area.
Rutherford’s atomic model is most likely called the Rutherford model or simply Rutherford model of the nuclear atom. It is to be seen to have a black big ball at the center as the nucleus and small red points moving around the nucleus are electrons as seen below. In a long line of the Bohr Family line as great physicists the most exemplary member in the authors opinion is Mr. Niels Bohr of Denmark. He took great advice from both great past physicists both J. J. Thomson and Ernest Rutherford. Which also led him to win a Nobel Prize in Physicists in 1922. One of his best researches was for his Model of the Atom, commonly named The Bohr Model.
In his version of the Model the neutrons and protons occupy a dense central region called the nucleus and the electrons orbit the nucleus much like planets orbiting the Sun. It is sometimes also called the planetary model because he theorized that the attractive gravitational force in a solar system and attractive electrical force between the positively charged nucleus and the negatively charged electrons in the atom are mathematically of the same form. As compared Below. V. S Another Great Austrian physicist in 1926 named Erwin Rudolf Joself Alexander Schrodinger, also created his own view of Atom.
He improved atomic models to a whole other level. Schrodinger used the new quantum theory to write and solve a mathematical equation describing the location and energy of an electron in a Hydrogen atom. Thus the quantum mechanical model was born. His view of the atom can be seen as “layers within layer” in terms of the electron shells. While not an accurate physical picture of what is happening with the electrons, it does allow to be visually grasp an otherwise concept. He says that each electron shell is made of a number of sub-shells. ( the number of sub-shells in a shell depends on what the shell number is).
In a picture it looks like this: The last and final physicist in this Atomic Theory is named Sir James Chadwick, CH, FRS, of the United Kingdom. In 1932, Chadwick proved that the atomic nucleus contained a neutral particle which had been proposed more than a decade earlier by Ernest Rutherford but he added the knowledge that it has the same mass as a proton. Now with the Neutron added, the atomic model seemed more complete than ever. The overall charges remained the same, and now there no longer seemed to be a discrepancy between the atomic and the atomic number. Picture exampled below.