THE ATOMIC THEORY

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The law of Simple Multiple Proprtions.. It was in the early 1800's that Johan Dalton proposed his atomic theory. Dalton noted, after working with carbon dioxide, that when making CO2, carbon combines with oxygen at a ratio of exactly one to two. He called his observation the Law of Simple Multiple Proportions. This led him to further his observations..

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THE ATOMIC THEORY

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1. THE ATOMIC THEORY FROM DALTON TO BOHR

2. The law of Simple Multiple Proprtions. It was in the early 1800’s that Johan Dalton proposed his atomic theory. Dalton noted, after working with carbon dioxide, that when making CO2, carbon combines with oxygen at a ratio of exactly one to two. He called his observation the Law of Simple Multiple Proportions. This led him to further his observations. need to note here how CO2 was madeneed to note here how CO2 was made

3. How compounds are formed Dalton then went one step further. His observation that masses of carbon and oxygen combine in precise proportions should hold true on the smallest scale. He reasoned that if the masses of the elements combined in precise proportions, then there must be a fixed ratio of atoms. Compounds have constant composition because they contain a fixed ratio of atoms.

4. Dalton’s Idea of the Atom Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were. we have already talked about different atoms having different atomic masses and different numbers of protons in their nucleiwe have already talked about different atoms having different atomic masses and different numbers of protons in their nuclei

5. One of the important reasons for talking about atoms is because the atoms combine with one another. That was an important part of the reason that Dalton came up with his atomic theory. He wanted to explain why compounds had fixed composition. But, as you will see, atoms combine in more ways than Dalton imagined.

6. J. J. Thompson and the Cathode Ray Tube Experiment J. J. Thompson did his research. Thomson built a cathode ray tube ending in a pair of metal cylinders with a slit in them. These cylinders were in turn connected to an electrometer, a device for catching and measuring electrical charge. When everything was hooked up, a glowing beam went from the cathode (-) to the anode(+)

7. A magnet affects the ray! Thompson wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. He found that when the rays entered the slit in the cylinders, the electrometer measured a large amount of negative charge. So whatever was coming out of the tube was negative.

8. The discovery of the electron. This experiment proves that something charged with negative electricity is shot off from the cathode, travelling at right angles to it, and that this something is deflected by the negative end of a magnet.

9. Thompson’s idea of the atom- the “Plum Pudding Model.” J.J. Thomson had discovered the electron. But, he didn’t know how the electron was placed in the atom. He visioned a sort of “plum pudding” atom. Thompson held that atoms were spheres of positively charged matter in which electrons were embedded.

10. Rutherford discovers the nucleus of the atom

13. The Gold Foil Experiment Gold was chosen because it is more malleable than any other material; this allowed the gold foil to be made extremely thin so the alpha particles would be scattered by a single gold atom as they passed through the foil. The effects of multiple scattering, involving several gold atoms, were greatly minimized by the extreme thinness of the foil. Deflected alphas were

14. The Bohr Model of the Atom.

15. The Bohr Model In the Bohr Model the neutrons and protons (symbolized by red and green balls in the adjacent image) occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun (but the orbits are not confined to a plane as is approximately true in the Solar System).

16. More of Bohr He envisioned specific discrete energy levels (i.e., shells) for the electrons within which they could move yet not emit radiation. Only if the electrons dropped to a lower energy level, or were raised to a higher level, would they emit or absorb electromagnetic radiation. That the energy of the emitted or absorbed radiation must equal the difference between the original and final energy levels of the electrons explained why atoms only absorb certain wavelengths of radiation.

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