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Atoms: The Greek Idea

Atoms: The Greek Idea

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Atoms: The Greek Idea

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  1. ~ 450 B.C.E., Leucippus and Democritus Atomos: Point at which matter can no longer be subdivided. Atoms: The Greek Idea

  2. ~384 B.C.E., Aristotle: All matter is composed of 4 elements, and all matter is continuous, not atomistic. Atoms: The Greek Idea

  3. THE ATOM • Around 450 B.C. a Greek philosopher, Democritus, proposed that all forms of matter were divisible into extremely small fundamental particles called atomos. (Greek for indivisible) • Due to world events, this concept was forgotten, replaced by the belief that matter was composed of four “elements” ; earth,wind, fire, & water. • From 1803 to 1810, John Dalton proposed the concept of the atom once again. Dalton backed his claim with experimentation.

  4. John Dalton and the Atomic Theory of Matter • 1803, John Dalton: Law of Multiple Proportions • Elements may combine in more than one set of proportions, each set corresponds to a different compound.

  5. John Dalton and the Atomic Theory of Matter • 1. All matter is composed of extremely small particles called atoms. • 2. All atoms of a given element are alike and differ from the atoms of any other element. • 3. Compounds are formed when atoms of different elements combine in fixed proportions. • 4. A chemical reaction involves the rearrangement of atoms.

  6. The modern atom is composed of subatomic particles.

  7. Subatomic Particles • ELECTRON: Properties discovered in 1897 by JJ Thompson • PROTON: Isolated and identified in 1919 by Ernest Rutherford • NEUTRON: Discovered by James Chadwick in 1932

  8. Nuclear Model of the Atom • Every atom contains an extremely small, extremely dense nucleus. • All of the positive charge and nearly all of the mass of an atom are concentrated in the nucleus. • The nucleus is surrounded by a much larger volume of nearly empty space that makes up the rest of the atom. • The space outside the nucleus is very thinly populated by electrons, the total charge of which exactly balances the positive charge of the nucleus.

  9. may come in one of three forms:

  10. Lavoisier: The Law of Conservation of Mass • Early 1700’s Lavoisier: Law of Conservation of Mass • During a chemical change, matter is neither created nor destroyed.

  11. Proust: The Law of Definite Proportions • 1799, Proust: Law of Definite Proportions • A compound always contains the same elements in certain definite proportions.