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Brief History of Atomic Theory

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Brief History of Atomic Theory 1st atomic models In 400 BC, the model looked like a solid indivisible ball Atomos Democritus theory: Matter could not be divided ... – PowerPoint PPT presentation

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Title: Brief History of Atomic Theory


1
Brief History of Atomic Theory
2
1st atomic models
  • In 400 BC, the model looked like a solid
    indivisible ball

3
Atomos
  • Democritus theory Matter could not be divided
    into smaller and smaller pieces forever
  • He named the smallest piece of matter atomos,
    an indivisible particle

4
  • This theory was ignored and forgotten for
    more than 2000 years!

5
Why?
Aristotle Plato thought earth, fire, air and
water were the elements. Alchemy used this model
for about 2000 years.
6
Daltons Model
  • In the early 1800s, the English chemist
  • John Dalton performed experiments that
    confirmed the idea of atoms.

7
Daltons Atomic Theory
  • All elements are made of indivisible atoms
  • Atoms of the same element are identical, but
    differ from atoms of other elements
  • Different elements atoms can combine to form
    compounds.
  • Reactions occur when atoms are separated, joined,
    or rearranged.
  • WHICH OF THESE ARE NO LONGER CONSIDERED TO BE
    TRUE ?

8
Thomsons Plum Pudding Model
  • In 1897, J.J. Thomson discovered that atoms
    are made of even smaller particles.

9
Thomson Model
  • Thomson used cathode ray tube
  • The ray consisted of negatively charged
    electrons.

10
Thomson Model
  • He proposed a model of the atom called the Plum
    Pudding model.
  • Atoms were made from a positively charged
    substance with negatively charged electrons
    scattered about, like raisins in a pudding.
  • Aka raisin pudding model

11
Millikan (1909)
  • OIL DROP experiment
  • Measures charge on electron


-
12
  • Rutherfords gold foil experiment (1911) Involved
    firing a stream of tiny positively charged
    particles at a thin sheet of gold foil (2000
    atoms thick)
  • Result most of space occupied by atom is empty
    space! Except for small, dense, positively
    charged NUCLEUS.
  • Positive particles named PROTONS
  • all protons are in the nucleus.

13
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14
Rutherford Nuclear Model
  • all of an atoms positively charged particles are
    contained in the nucleus. The negatively charged
    particles were scattered outside the nucleus.

15
Bohr Model
  • In 1913, the Danish scientist Niels Bohr proposed
    that each electron is in a specific energy level.

16
Bohr Model
  • According to Bohrs atomic model, electrons move
    in definite orbits around the nucleus, much like
    planets circle the sun.

17
Wave Model Louis DeBroglie (1924) es have
wavelike properties
18
Wave Model Erwin Schrodinger (1927) Quantum
mechanics model es location probability
19
Chadwick (1932)
  • Discovers particle with same mass as proton but
    no charge the
  • NEUTRON

20
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21
Indivisible Electron Nucleus Orbit Electron Cloud
Greek X
Dalton X
Thomson X
Rutherford X X
Bohr X X X
Wave X X X
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