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Atomic Model Theory

Atomic Model Theory. Early Greek Models. Who was right? Aristotle was wrong. However, his theory persisted for 2000 years. Democritus (400 b.c .). Aristotle (350 b.c ). Thought matter could not be divided indefinitely Led to the idea of atoms in a void.

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Atomic Model Theory

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  1. Atomic Model Theory

  2. Early Greek Models Who was right? Aristotle was wrong. However, his theory persisted for 2000 years. Democritus (400 b.c.) Aristotle (350 b.c) • Thought matter could not be divided indefinitely • Led to the idea of atoms in a void • Modified an earlier theory that matter was made of four “elements”: earth, fire, water, air

  3. John Dalton (1766 – 1844) • “Billiard Ball” Model • 1800 – proposed a modern atomic model based on experimentation, not on pure reason • Performed a number of experiments that eventually led to the acceptance of the idea of the atoms in 1803 • Postulates • All matter is made of atoms. • Atoms of an element are identical. • Each atom has different atoms. • Atoms of different elements combine in constant ratios to form compounds. • Atoms are rearranged in reactions. • His ideas account for the law of conservation of mass.

  4. JJ Thomson (1856 – 1940) “Plum Pudding” or “Cookie Dough” Model • Discovered the electron in 1897 • Atoms were made from a positively charged substance with a negatively charged substance scattered about, like raisin in a pudding or chips in a chocolate chip cookie.

  5. Ernest Rutherford (1871 – 1937) Gold Foil Experiment • Atoms mostly empty space and not filled with a positively charged material • Small positive charged center (nucleus) • Negatively charged particles around the nucleus

  6. Neils Bohr (1885 – 1962) Planetary Model • Found that electrons move in definite orbits or energy levels around the nucleus in 1913 • Electrons orbit the nucleus in “shells”.

  7. Electron Cloud Model Current Model • Describes a cloud-like region where the electron is likely to be found • Can not say with certainty, where the electron actually is at any point in time, yet can describe where it ought to be • Cloud represents a history where the electron has probably been and where it is likely to be going

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