https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo en-us 2022-02-17 09:16:16 UTC 2022-02-19 04:07:54 UTC hello@padlet.com johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052873271 The atom's history begins around 450 B.C. with Democritus, a Greek philosopher Democritus wondered what would happen if a piece of matter, such as an apple, was cut into smaller and smaller pieces. He predicted that matter would reach a point where it could no longer be cut into smaller pieces. He referred to these "uncuttable" pieces as atomos. This is the origin of the modern term atom.

Democritus was an important philosopher. However, he was less influential than the Greek philosopher Aristotle, who lived about 100 years after Democritus. Aristotle rejected Democritus’s idea of atoms. In fact, Aristotle thought the idea of atoms was ridiculous. Unfortunately, Aristotle’s ideas were accepted for more than 2000 years. During that time, Democritus’s ideas were more or less forgotten.]]> 2022-02-17 10:10:02 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052873271 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052879664 Atoms are extremely small. They could not be seen prior to the invention of scanning tunneling microscopes in 1981. The concept of atoms, on the other hand, dates back to ancient Greece.]]> 2022-02-17 10:13:52 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052879664 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052882555 Around the year 1800, a British chemist named John Dalton resurrected Democritus' early ideas about the atom. He earned a living as a teacher and only did research in his spare time. Nonetheless, based on his research findings, he developed one of science's most important theories.]]> 2022-02-17 10:15:31 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052882555 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052886527 Dalton conducted numerous experiments that provided evidence for the existence of atoms. He studied the pressure of gases, for example. He deduced that gases must be made up of tiny particles in constant motion. Dalton was also interested in the properties of compounds. He demonstrated that a compound always contains the same elements in the same proportions. Different compounds, on the other hand, are always made up of different elements or ratios. This is only possible, Dalton reasoned, if elements are made of tiny particles that can combine in an infinite number of ways. Dalton developed a theory of the atom based on his research.]]> 2022-02-17 10:18:00 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052886527 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052899897 The discovery of electrons was the next major breakthrough in the history of the atom. These were the first subatomic particles discovered. J. Thomson, a British physicist, discovered them in 1897. Thomson was fascinated by electricity. He conducted experiments in which an electric current was passed through a vacuum tube. Thomson's experiments demonstrated that an electric current is made up of negatively charged particles that flow. What was the significance of this discovery? Many scientists at Thomson's time believed that electric current is made up of rays, similar to light rays, and that it is positive rather than negative. Thomson's experiments also revealed that negative particles are all identical and smaller than atoms. Thomson came to the conclusion that negative particles could not be fundamental units of matter because they are all the same. Instead, they must be atom fragments. The negative particles were later referred to as electrons.]]> 2022-02-17 10:26:18 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052899897 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052966764 Rutherford discovered that some elements emit positively charged particles in 1899. He referred to them as alpha particles (α). In 1911, he studied atoms using alpha particles. He directed an alpha particle beam at a very thin sheet of gold foil. He placed a screen of material outside the foil that glowed when alpha particles struck it. Based on his findings, Rutherford concluded that some of an atom's charge is concentrated in a small central area with enough mass to deflect alpha particles. He referred to this area as the nucleus. Rutherford later discovered that positively charged particles exist in the nucleus. He gave the positive particles the name protons. Rutherford also predicted that neutrons would exist in the nucleus. However, he was unable to locate them. In 1932, one of his students, physicist James Chadwick, discovered neutrons.]]> 2022-02-17 11:11:48 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2052966764 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2053076485 In 1932, physicist James Chadwick conducted an experiment in which he bombarded Beryllium with alpha particles derived from Polonium's natural radioactive decay. The resulting radiation had a high penetration through a lead shield, which could not be explained by the particles available at the time.

Chadwick's interpretation problems vanished quite naturally with the postulate of an uncharged (neutral) particle of about the same weight as a proton. Thus, his findings could be explained by known natural laws, particularly those governing energy and momentum conservation.

Later experiments confirmed the discovery, which was especially impressive in light of Meitner, Hahn, and Strassmann's discovery of nuclear fission at Christmas 1938.]]> 2022-02-17 12:35:15 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2053076485 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056213246 2022-02-19 04:05:24 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056213246 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056213681 2022-02-19 04:06:16 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056213681 johnarguilles https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056214446 2022-02-19 04:07:54 UTC https://padlet.com/johnarguilles/gmzwjs5hc2s6niyo/wish/2056214446