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Lab Tips in Atoms, Molecules, and Ions

Protons, Neutrons, and Electrons Lab

There are some important little facts about subatomic particles that everyone should know. When we say subatomic particles, we mean a particle smaller than an atom, such a proton, neutron, and an electron.

First thing's first, protons and neutrons are in the center of the atom, making up the nucleus. Electrons surround the nucleus in shapes that we call orbitals. Protons have a positive charge, electrons have a negative charge, and neutrons have no charge.

Since opposite charges attract, protons and electrons attract each other. We can demonstrate and explain this phenomenon in a simple lab. The only things you'll need are:

A plastic grocery bag
Small confetti-sized pieces of paper

Let's do this thing.

  1. Use the scissors to cut 2 strips of plastic from the grocery bag. Try to make the strips about 4 cm wide and 20 cm long. No need to be super exact though.
  2. Hold the freshly cut plastic strip at one end with one hand then grasp the plastic strip between the thumb and fingers of your other hand just below the first hand.
  3. Now, use your first hand to quickly pull the plastic strip through your thumb and fingers of the other hand. Repeat this process three or four times then stop.
  4. Finally, use your first hand to lightly grasp the end of the plastic piece and let it hang loosely. Then, bring your other hand near it.

What happens?

Hopefully you observe that the plastic piece magically jumps closer to your hand as it slowly approaches. We know it's not really magic, but it is chemistry in action. If for some reason the plastic doesn't jump towards your hand, try the whole process over again.

What's going on with this system?

As you held the plastic between your fingers, the number of protons and electrons in your fingers and the plastic was the same. Consequently, both your fingers and the plastic were neutrally charged. When you pulled the plastic through your fingers, electrons from your skin jumped onto the plastic. At this point the plastic had more electrons than protons meaning the plastic had a net negative charge. What do you think happened with your fingers? Because they gave up some electrons, your fingers ended up with a slight positive charge.

Can you see where this is going? In the process of rubbing your fingers against the plastic you electrically charged the plastic. Then when you slowly brought your positively charged fingers closer to the negatively charged plastic, opposites attracted just like Paula Abdul predicted. The positive skin and the negative plastic attract each other because positive and negative attract.

Let's try a different variation and see if you can explain what's going on.

Charge two strips of plastic (steps 2 and 3 above) and bring them close to each other.

What happens?

We've already explained that rubbing the plastic through your fingers makes it obtain a negative charge. When you bring two negatively charged pieces of plastic together the like-charges repel each other and the pieces of plastic will jump away or repel each other.

You can try out this same sort of experiment by blowing up a balloon and rubbing it against your clothes. Try moving the balloon close to paper, walls, and even a stream of water to see what happens.

Check out these videos that might help clear up some lingering confusion.

Static Electricity Detection by Water

Bending Water

How Static Electricity Works

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