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Atomic Theory

Atomic Theory. Foundations of Atomic Theory. Particle theory supported as early as 400 B.C Democritus- coined term atom (means indivisible) Aristotle- all matter was continuous Ideas accepted for nearly 2000 years Modern definition of element accepted by 1700s

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Atomic Theory

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  1. Atomic Theory

  2. Foundations of Atomic Theory • Particle theory supported as early as 400 B.C • Democritus- coined term atom (means indivisible) • Aristotle- all matter was continuous • Ideas accepted for nearly 2000 years • Modern definition of element accepted by 1700s • Elements known to combine to form compounds • Do they always combine with the same ratio when forming particular compounds? • Improved technology leads to accurate measurements of elements and compounds • Leads discovery of several basic laws

  3. Law of conservation of mass • Matter can neither be created nor destroyed during ordinary chemical reactions • Law of definite proportions • A particular chemical compound will always contain the same elements in the same proportions, no matter what the sample size or source • Law of multiple proportions • If two or more different compounds are composed of the same elements then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small numbers • CO vs. CO2

  4. Dalton’s Atomic Theory • All matter is composed of extremely small particles called atoms • Atoms of a given element are identical in size, mass, and other properties • Atoms of different elements differ in size, mass, and other properties • Atoms cannot be subdivided, created, or destroyed • Atoms of different elements combine in simple whole-number ratios to form compounds • In chemical reactions, atoms are combined, separated, or rearranged

  5. Modern Atomic Theory • What is true from Dalton’s theory: • All matter is made of atoms • Atoms of one element differ in properties from atoms of another • What was modified from Dalton’s Theory • Atoms can be subdivided

  6. Organizing the elements • Mendeleev and Moseley • Mendeleev- created first periodic table, arranging elements by atomic mass and chemical properties • Was able to predict the discovery of new elements based on chemical properties • Some elements, however could not be put in order by atomic mass • Moseley- elements could be better organized if arranged by atomic number

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