Democritus created the first atomic model (a round sphere with no electrons, protons, or neutrons). To them, human reasoning was superior to experimentation. Instead, they use reasoning to back up their beliefs. However, philosophers are not scientists nor do they test their ideas. These pursuits contributed to early chemical knowledge but were often shrouded in mysticism and superstition. Ancient Greeks considered Aristotle’s opinions as “very important” and if Aristotle thought the atomic idea had no merit, then most of these Greeks thought the same as well.ĭuring the Middle Ages and the Renaissance, scientists pursued various goals, including the transmutation of base metals into gold and the discovery of the philosopher’s stone. In fact, Aristotle dismissed the atomic idea as worthless. Unfortunately, the atomic ideas of Democritus had no lasting effects on other Greek philosophers, including Aristotle. Aristotle postulated that all matter was made of only four elements – Earth, Air, Water and Fire. Aristotle believed in the continuous and infinitely divisible nature of matter. He was the first person to use the word “atom”/ Life Persona.Īristotle, a prominent philosopher of the time, rejected the atomic theory in favour of his own ideas, which dominated scientific thought for centuries. The theory of the composition of the atom continues to be an ongoing and exciting adventure.Greek philosopher, Democritus (460–370 B.C.). The quarks themselves are in turn made of vibrating strings of energy. The atomic theory has been further enhanced by the concept that protons and neutrons are made of even smaller units called quarks. Also, new elements have been created by bombarding existing nuclei with various subatomic particles. Since 1932, through continued experimentation, many additional particles have been discovered in the atom. With the discovery of the neutron, an adequate model of the atom became available to chemists. This particle became known as the neutron. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. In 1932, James Chadwick bombarded beryllium atoms with alpha particles. Until 1932, the atom was believed to be composed of a positively charged nucleus surrounded by negatively charged electrons. Thus, this model introduced the concept of sub-energy levels. Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. This model can be portrayed as a nucleus surrounded by an electron cloud. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This atomic model is known as the quantum mechanical model of the atom. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr atom model one step further. The orbit nearest the nucleus has an energy of E1, the next orbit E2, etc.ģ. Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower orbit.Ĥ. The energy and frequency of light emitted or absorbed can be calculated by using the difference between the two orbital energies. Those orbits are stable and are called "stationary" orbits.Ģ. Each orbit has an energy associated with it. The Bohr model can be summarized by the following four principles:ġ. Electrons occupy only certain orbits around the nucleus. This model is patterned on the solar system and is known as the planetary model. He proposed that electrons are arranged in concentric circular orbits around the nucleus. In 1913, Neils Bohr, a student of Rutherford's, developed a new model of the atom.
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