1-1: Charges and Atoms

Particles Inside Atoms

In the Chemistry unit, you looked at the structure of the atom:

The three basic subatomic particles are the proton, neutron and electron. You have seen this information before, but it's good to review:

While protons and neutrons are important for atoms, here everything inside the nucleus is locked up and has no effect. The only thing we need to pay attention to are the electrons. This is why the word electricity, which refers to a form of energy carried by electrons, sounds so much like that subatomic particle.

There are two types of electricity:

• static electricity, which is a type of electricity that can stay in one place for a long time before it jumps somewhere else

• current electricity, which can flow smoothly through materials called conductors and can be easily controlled and used

These types of electricity are quite different, but in both cases, only the electrons move. Protons and neutrons stay in the nucleus and are not involved in either static or current electricity.

Charged Objects

If you have a neutral object, that means the number of positive charges equals the number of negative charges. We can represent the charges in the object like this:

Obviously a real object would have many more charges than this. We can't show them all, so we'll just show a representative sample, with + meaning a positive charge (proton) and – meaning a negative charge (electron).

In the picture of the object above, count the number of + and – charges: they are equal. This is true of all neutral objects.

If the object loses some negative charges (we'll see how this is possible later), this can happen:

This is a positively charged object since it has more positive charges than negative charges. Note that the positive charges stay in the same place, and only the negative charges (electrons) move.

But, if the object gains some negative charges, this can happen:

This is a negatively charged object since it has more negative charges than positive charges. Again, note that the positive charges stay in the same place. The object has somehow gained electrons.

We say that we have a charged object if it is either positively or negatively charged. Neutral objects are not charged objects.

This goes a little bit beyond what we're looking at right now, but it gives you a good overview about where we're going with static electricity:

Electroscopes

An electroscope is a device that can tell you if an object that you bring near it is a neutral object, or if it has some sort of charge. Electroscopes can be built a few different ways, but two of the main types of electroscopes are called pith ball electroscopes and metal leaf electroscopes.

Pith ball electroscopes are very simple devices, which normally have one or two small shapes, usually rounded, at the end of a string hung from a curved arm. The shapes are usually made of a material like Styrofoam, covered in a thin layer of paint which can carry electric current.

Here is a simple pith ball electroscope showing that a plastic rod or a Styrofoam plate rubbed on a cat carries an electric charge:

The ball is attracted to the rod and the plate. This is how the pith ball electroscope shows that an object is charged in some way.

Metal leaf electroscopes are a bit more complicated but are also very good at showing if an object is charged or not.

There is a ball on top (sometimes it's a flat plate) made of some kind of metal. This is connected using a rod to one or two metal "leaves" inside the device. These leaves are thin pieces of metal foil, which can move apart if the object brought near the ball is charged in some way.

Here is a good video showing a teacher demonstrating how to use a metal leaf electroscope:

You may be doing some experiments involving one or both kinds of electroscopes. Each of them are good at doing some things, but not good at doing other things. It's important to choose the right piece of equipment for your experiment, and to use it properly.

Practice

The Basics

1. Which subatomic particles inside the atom are involved in electricity?

2. If an object has a positive charge overall, are there more protons or electrons in that object?

3. Name the two different types of electroscopes described above.

Extensions

1. When objects go from neutral to charged, what happens to the protons, if anything?

2. How does a metal leaf electroscope show that an object has a charge?

3. Why do the words "electricity" and "electron" sound so similar?