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 What is an atom?  Draw a picture to go with your explanation.

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Presentation on theme: " What is an atom?  Draw a picture to go with your explanation."— Presentation transcript:


2  What is an atom?  Draw a picture to go with your explanation.

3 “Sunday Afternoon on the Island of La Grande Jatte” by Georges Seurat

4  430 B.C. in Greece  Philosopher, Democritus came up with an idea  Said that matter is formed from small pieces that can’t be cut into smaller parts  Called “atomos”  Means uncuttable  No experiments to prove atoms existed until the 1600’s

5  John Dalton, 1766-1844  English Chemist  Proposed an atomic theory  Elements are composed of atoms that can’t be divided  Atoms of the same element are exactly alike. Atoms of different elements are different.  Atoms of one element can’t be changed into an atom of a different element.  Atoms can’t be created or destroyed in any chemical change, only rearranged.  Every compound is made of atoms of different elements, combined in a specific ratio.

6  J.J. Thomson, British scientist  1897, found that atoms contain negatively charged particles  Scientists knew that atoms had no electrical charge  Thomson proposed that atoms must also have a positive charge to cancel the negative charge.

7  Student of Thomson  Tested Thomson’s theory  Predicted that charged particles would pass through the foil in a straight line.  Thought the gold atoms wouldn’t have enough positive charge to repel the other particles.

8  Found that most particles pass through the foil  Some were also deflected  Rutherford knew that like charges repel  Decided that the positive charge must be in the center of an atom, called a nucleus  Particles deflected, must have hit the nucleus of gold atoms

9  Niels Bohr, Danish scientist  Student of Thomson and Rutherford  Created a model where electrons were in orbits around the nucleus based on the amounts of energy they had

10  Read p. 106-108  Complete the following WINK:  What is the correct model of an atom?  Compare and contrast it to other models.  Draw a picture to go with your explanation. (Should be ½ page or more, in your own words)

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