Glossary of Chapter 3 Notes

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450 BC An atom is the smallest particle of an element that retains the chemical idenity of that element.
Conservation of matter
Law of Constant composition
For any given compound, the elments are always in the same porportion by mass.
Atomic Theory. All matter is composed of atoms which are small and indivisable. There are 4 postulates to his theory, not all 4 were totally correct.
Dalton's Postulates
The Correct ones
1. Each element is composed of extremely small particles called atoms.
2. A given compound always has the same relative numbers and kinds of atoms.
Benjamin Franklin
Discovered the existance of positive and negative charges.
J.J Thompson
Discovered that atoms were not indivisible balls, but had structure. Atoms of all substances contain the same kind of negative particles (electrons). Plum pudding model of atom which has an equal number of positive and negative charges.
Discovered a charge of an electron.
Accidentally discovered uranium ore (pitchblend) emitted vadiation, like Roentgen's discovery of X-rays.
Dalton's Postulates
The Uncorrect Ones
All atoms of a given element are identical and they differ from those of any other element.
This is incorrect because of Isotopes.

Atoms are neither created nor destroyed in chemical reaction
- IN nuclear chemical reactions you can create and destroy different atoms.
- Create fusion - 2H + 3H equals 4 He+ 1n0
Destroy fission 236O equals 141Ba + 92 kr + 31n0
Marie Curie
Discovered radium and Polonium. She worked with her husband Pierre. Her one daughter Irene also studied radioactivity she and her husband discovered that radioactive substances not only exist in nature, but could be produced artificially when certain elements were bombarded with alpha particles.
Gold Foil experiment that improved the model of the atom Gold foil 20000 atoms thick. Alpha particles (He2+) were shot at the gold foil; 1/8000 alpha particles were deflected. Proposed that the atom contains a nucleus. Based on their calculations, if the atom was the size of a dome, the nucleus would be about the size of a dime.
e- -1 9.11 * 10-28
p+ +1 1.67 * 10-24
n0 0 1.67 * 10-24

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