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The atomic theory
By Qit Villorante
An “atom” is the smallest particle into which an element can be divided and can still be the same substance and a “theory” is a unifying explanation for a broad range of hypotheses and observations that have been supported by testing. Atoms are so small that, until recently, no one had ever seen one. But ideas, or theories, about atoms have been around for over 2,000 years. The first written account of this concept was made by Greek philosophers. The Greeks were held in high esteem during that time because of their scholarly work, upon which most scientific studies were based.
Such people were known because of their contribution on the development of the atomic theory and some of them were Aristotle, Democritus, John Dalton, Eugen Goldstein, John Joseph Thomson, Ernest Rutherford, Niels Bohr and James Chadwick together with their respective atomic models.
By Qit Villorante
An “atom” is the smallest particle into which an element can be divided and can still be the same substance and a “theory” is a unifying explanation for a broad range of hypotheses and observations that have been supported by testing. Atoms are so small that, until recently, no one had ever seen one. But ideas, or theories, about atoms have been around for over 2,000 years. The first written account of this concept was made by Greek philosophers. The Greeks were held in high esteem during that time because of their scholarly work, upon which most scientific studies were based.
Such people were known because of their contribution on the development of the atomic theory and some of them were Aristotle, Democritus, John Dalton, Eugen Goldstein, John Joseph Thomson, Ernest Rutherford, Niels Bohr and James Chadwick together with their respective atomic models.
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Aristotle a philosopher did not believe in the atomic theory and he thought that all materials on Earth were not made up of atoms but of the four nature elements, Earth, Fire, Water, and Air. Most people followed Aristotle’s idea, causing Democritus’ idea--- which was that all substances on Earth were made of small particles called “atoms”--- to be overlooked for about 2,000 years. Aristotle’s view was finally proven incorrect and his teachings are not present in the modern view of the atom.
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Democritus (440 B.C.) stated that all materials on Earth were made up of very tiny particles. He proposed that there is a substance that if you kept cutting in half forever, eventually you would end up with an “uncuttable” particle. He called these particles “atomos” meaning not to be cut and is known as “atom”. Democritus thought that atoms were small, hard particles of a single material and in different shapes and sizes. He thought that atoms were infinite in number, always moving and formed different materials by combining with each other.
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John Dalton (1803) claimed that the combination of elements to form compounds is because elements are made of atoms. He published his own three-part atomic theory:
1) All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.
2) Atoms of the same element are exactly alike, and atoms of different elements are different.
3) Atoms join with other atoms to make new substances.
1) All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed.
2) Atoms of the same element are exactly alike, and atoms of different elements are different.
3) Atoms join with other atoms to make new substances.
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Eugen Goldstein (1886) noted that cathode-ray tubes with a perforated cathode emit a glow from the end of the tube near the cathode. Goldstein concluded that in addition to the electrons, or cathode rays, that travel from the negatively charged cathode toward the positively charged anode, there is another ray that travels in the opposite direction, from the anode toward the cathode. Because these rays pass through the holes, or channels, in the cathode, he called them “canal rays”.
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John Joseph Thomson (1897) used a cathode-ray tube to conduct an experiment which showed that there are mall particles inside atoms. This discovery identified an error in Dalton’s atomic theory. Atom can be divided into smaller parts. Because the beam moved away from the negatively charged plate and toward the positively charged plate, Thomson knew that the particles must have a negative charge. He called these particles corpuscles. We now call these particles “electrons” which are the negatively charged particles found in all atoms. Thomson changed the atomic theory to include the presence of electrons. He knew there must be positive charges present to balance the negative charges of the electrons, but he didn’t know where. Thomson proposed a model of an atom called the “plum-pudding” model, in which negative electrons are scattered throughout soft blobs of positively charged material.
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Ernest Rutherford’s (1909) model says that most of the atom’s mass is found in a region in the center called the “nucleus” which is a tiny, extremely dense, positively charged region in the center of an atom and he calculated that it is 100,000 times smaller than the diameter of the atom. In his model, half of the atom is mostly empty space, and the electrons travel in random paths around the nucleus.
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Niels Bohr (1913) depicts atom as small, positively charged nucleus surrounded by electrons which travel around in circular orbits--- similar to the structure of the solar system but with attraction provided by electrostatic forces rather than gravity. These paths are located at certain “levels” from the nucleus. Electrons cannot travel between paths, but they can jump from one path to another.
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James Chadwick made a fundamental discovery in the doorman of the nuclear science. He proved and discovered the existence of the fourth subatomic particle known as “neutrons” in atom. He also established that atomic number is determined by the number of protons in an atom.