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  1. Problems
  2. /In one gold foil experiment, about 1 alpha particle in 8000 bounces back…
MediumChemistryHigh School (9–10)GeneralStructure of the Atom › Subatomic Particles and Atomic ModelsNumericalBoard Exam

In one gold foil experiment, about 1 alpha particle in 8000 bounces back…

StemPy LabContributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

In one gold foil experiment, about 111 alpha particle in 800080008000 bounces back.

  1. About how many bounce back if 48 00048\,00048000 alpha particles are fired?
  2. And if 1 200 0001\,200\,0001200000 are fired?
  3. In (a), how many pass through or are turned only a little?

Check your answer

Work it out on paper, then type your number. The answer itself stays hidden.

Need a reminder? The key ideaShowHide

In the gold foil experiment, most alpha particles passed straight through, a few were turned, and a very few bounced back. So an atom is mostly empty space, with a tiny, heavy, positive nucleus at its centre. The atom is about 100 000100\,000100000 times wider than its nucleus.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

Step 1. (a) 48 0008000=6\dfrac{48\,000}{8000} = 6800048000​=6 particles bounce back.

Step 2. (b) 1 200 0008000=150\dfrac{1\,200\,000}{8000} = 15080001200000​=150 particles bounce back.

Step 3. (c) 48 000−6=47 99448\,000 - 6 = 47\,99448000−6=47994 particles get through.

Answer: (a) about 666. (b) about 150150150. (c) 47 99447\,99447994.

What it shows. Almost every particle misses the nucleus, so the nucleus must be tiny.

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  1. Thomson's and Rutherford's modelsInside the Atom: Particles and Models

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