Lesson_5.1a_Printable_PPT

Lesson_5.1a_Printable_PPT - Atom and Atomic Structure In...

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Atom and Atomic Structure In the fifth century B.C., Leucippus (loo-KIP-us) suggested that all matter -- everything -- was made up of a few simple building blocks. He managed to convince a number of people including Democritus who believed that matter was made up of particles so small that they could not be further subdivided. Democritus postulated that different substances has different roperties because of the differences in the nature of their "atoms." properties because of the differences in the nature of their "atoms." However, his theories were not supported by Aristotle, 300 BC, who thought that matter was continuous, not discrete. He advocated that every object on the earth was made up of some combination of only four substances: earth, water, fire, and air. It took over 2000 years for Aristotle's philosophy to be replaced by the concept that matter was not just composed of only those four general substances to its being comprised of unique elements - hydrogen, carbon, oxygen, sulfur, etc.
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Dalton’s Atomic Theory In the early 1800s, the English Chemist John Dalton revived the idea of atom and summarized his theory in five statements. 1. Indivisible minute particles called atoms make up all matter. 2. All the atoms of an element are exactly alike in shape and mass. 3. The atoms of different elements differ from one another in their mass. 4. Atoms chemically combine in definite whole number ratios to form chemical compounds. 5. Atoms are neither created nor destroyed in chemical reactions. Many scientists at that time were skeptical of the concept of atom because it could not be observed directly. The discovery of electron by J. J. Thomson changed all this.
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J J Thomson and the Electron At the Cavendish Laboratory at Cambridge University, Thomson was experimenting with electric current inside evacuated glass tubes. He suggested that these mysterious rays
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Lesson_5.1a_Printable_PPT - Atom and Atomic Structure In...

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