What is an atom? Draw a picture to go with your explanation.
“Sunday Afternoon on the Island of La Grande Jatte” by Georges Seurat
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
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.
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.
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.
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
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
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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