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10/4/2015 The Indivisible Unit 3: Atomic Structure - The Nucleus Lesson 3.1: Early Ideas about Matter 1 Lesson 3.1 Early Ideas About Matter • Compare and contrast the atomic models of Democritus, Aristotle, and Dalton. p the • Understand how Dalton's theoryy explains conservation of mass. 2 Lesson 3.1 Early Ideas About Matter Dalton’s Atomic Theory The ancient Greeks tried to explain matter, but the scientific study of the atom began with John Dalton in the early 1800's. 3 1 10/4/2015 What’s the Smallest Thing Around? The atom: From the greek “atomos”- “indivisible” = Can’t be seen 1 gram of hydrogen gas: 60,200,000,000,000,000,000,000 atoms 4 Greek Philosophers • Many ancient scholars believed matter was composed of such things as earth, water, air, and fire. • Many believed matter could be endlessly divided into smaller and smaller pieces. 5 Greek Philosophers • Democritus (460–370 B.C.) was the first person to propose the idea that matter was not infinitely divisible, but made up of individual particles called atomos. • He believed that atoms were indivisible and indestructible • Aristotle (484–322 B.C.) disagreed with Democritus because he did not believe empty space could exist. • Aristotle’s views went unchallenged for 2,000 years until science developed methods to test the validity of his ideas. 6 2 10/4/2015 Greek Philosophers • John Dalton revived the idea of the atom in the early 1800s based on numerous chemical reactions. • Dalton’s atomic theory easily explained conservation of mass in a reaction as the result of the combination, separation, or rearrangement of atoms. 7 Dalton’s Atomic Theory (experiment based!) 1) All elements are composed of tiny indivisible particles called atoms John Dalton (1766 – 1844) 2) Atoms of the same element are identical. Atoms of any one element are different from those of any other element. 8 Dalton’s Atomic Theory (Cont.) 3) Atoms of different elements combine in simple whole-number ratios to form chemical compounds 4) In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element. 9 3 10/4/2015 Section 3.1 Assessment Who was the first person to propose the idea that matter was not infinitely divisible? A. B. C. D. Aristotle Plato Dalton Democritus 10 Section 3.1 Assessment Dalton’s theory also conveniently explained what? A. B. C. D. the electron the nucleus law of conservation of mass law of Democritus 11 4