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3-2 Discovering Atomic Structure. Michael Faraday ► Suggested that the structure of atoms is related to electricity, and it turns out that atoms contain.

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Presentation on theme: "3-2 Discovering Atomic Structure. Michael Faraday ► Suggested that the structure of atoms is related to electricity, and it turns out that atoms contain."— Presentation transcript:

1 3-2 Discovering Atomic Structure

2 Michael Faraday ► Suggested that the structure of atoms is related to electricity, and it turns out that atoms contain particles that have electrical charge.

3 Static Electricity ► Benjamin Franklin is one of the first to experiment with electricity. ► Concludes that electricity has two kinds of charges.  Positive (+)  Negative(-)

4 Cathode Rays and Electrons ► Running electricity through a partially evacuated glass tube occurs in a cathode tube.

5 ► The negative end is called a cathode. ► The positive charged end is called an anode ► When lined with a fluorescent material and passing electricity through it, you can see the radiation going through it.

6 ► It was found that putting a magnet near the particles deflects them, indicating a negative charge of particles ► J.J. Thomson experimented with cathode rays, with a magnet, and charged plates near the ray.

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8 ► Discovered  Magnetic and electric fields deflect the rays  Deflects rays in predictable ways  The particles are Negative in charge  Particles come from cathode  Named the particles Electrons  Meant Atoms were made smaller parts!!!!  Particles had a charge of 1.76 x 10 8 coulombs/gram

9 Robert Millikan ► Oil Drop Experiment  Gave droplets of oil a negative charge using x-rays  Droplets fell between two charges plates.  Measured how the charge on the plates affected the rate of fall of oil drops.  Found the charge to be 1.60 x coulombs  From Thomson's findings he could calculate the mass of a single electron.  9.11 x grams

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11 ► Problem:  how could matter containing electrons be neutral and where was all the mass?  His findings were 1/2000 the mass of an atom.

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13 Radioactivity ► Radioactive elements are found in the late 1800’s. Henri Becquerel was the first to discover radioactivity ► Marie Curie and her husband Pierre find two radioactive elements after Becquerel

14 Ernest Rutherford ► See Figure 3-13 in book ► Discovers alpha particles  Deflects towards negative plate ► Discovers beta particles  Deflect towards positive plate ► Discovers gamma particles  Not affected by electric plates

15 The Nuclear Atom ► J.J. Thomson's problem again: if electrons are negative, why are atoms neutral? ► Must contain positive parts equal to the negative parts. ► Where are they?  The Plum Pudding Model  All particles evenly distributed.  Rutherford changes this concept

16 The Gold Foil Experiment (figure 3-14)

17 mag/java/rutherford/ ► Most particles passed through gold without a problem ► 1 in 8000 alpha particles deflected ► These were sent in ALL directions including straight back!

18 What does this mean? ► Most of the atoms positive charge, as well as the mass is in the middle, called the nucleus. ► Most pass through the empty space but occasionally one gets close enough to the positive nucleus to deflect


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