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Bite-Size Physics

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Last lesson we spent time on atoms. We learned what they are and what they are made of. This lesson we are going to learn more about what they do and how they do it. The key to understanding the mysteries of what atoms do (and the key to understanding how electromagnetic energy works) is to try to understand the electron. I say try to understand because the electron does not work like anything else you are familiar with. Like I said in the last lesson, it is one wacky little fellow.


Electron “Orbits”

Remember, that atoms are made up of protons and neutrons that are in the center of an atom (the nucleus) and electrons that are moving around outside the nucleus. Now hold on to your hats, here’s where things start to get a bit goofy. Electrons don’t really move around the nucleus...they pop in and out of existence around the nucleus. They exist in one spot, then “pow”, they disappear and reappear in another spot. Then “boink” off they go again and “zip” they are back again. Here’s a fun question...where do they go? That’s an answer that, at this point, nobody knows. You may run into some older books or websites that still refer to electrons orbiting around the nucleus like the planets orbit around the sun. That’s the way folks used to think it worked, but lo and behold, the teeny tiny electron is like nothing else in the universe.


Electron Shells

So why did they ever think electrons orbited the nucleus? Well, just like the Earth stays a certain distance from the Sun, the electron stays a certain distance from the nucleus as it pops in and out of existence. The reason they stay a certain distance is due to one of the strangest things in science and that’s the wave/particle duality nature of electrons. Electrons act like waves, and like particles at the same time! That concept is one of the keys to quantum physics and gets a little deeper (like seventeen miles deeper) than we are going to go in this lesson, so we’ll leave it at that for now. Suffice it to say that they do stay a certain distance from the nucleus. Since scientists are trying to get away from the “orbit” concept, they are now calling these areas the electrons move in “shells”. A nice way to visualize this is to think about a balloon with a teeny tiny ball bearing in the middle of it. The ball bearing would represent the nucleus and the balloon would represent the shell. The electrons could be anywhere on the skin of the balloon at any given time. It is this “shell” that gives the atom its body. The electron moves so fast that it actually provides a balloon like shell around the atom and so the atom can be squooshed but not smashed. These balloons, made of several fast moving particles, are what give tables, chairs, walruses, and cheese burgers their structure. Let’s try another way to look at this. You’re playing miniature golf and you come to the old wind mill hole. Your friend takes a shot and since the blades of the windmill are going nice and slow he gets the ball right through. Now it’s your turn. Suddenly you hear a zap and a pow and sparks go flying. Something has gone wrong with the wind mill and it starts spinning at amazing speeds. You decide to give it a try and hit the ball towards the wind mill. Well since it is spinning out of control, those blades now form almost a solid disk so that there is no way your ball can get through the wind mill. Electrons do the same thing. They move so fast that even though there may not be many of them, they form a shell that can’t be penetrated. (To be clear, particles that are smaller than an atom can go through the shells and pop out the other side.)

Let’s go a little further with this shell thing. An atom can have as few as one and as many as seven shells. Imagine our balloon again. Now there can be a balloon inside of a balloon inside a balloon and so on. Up to seven balloons! Each balloon, whoops, I mean shell, can have only so many electrons in it. This simple equation 2n2 tells you how many electrons can be in each shell. The n stands for the number of the shell. The first shell can have up to 2 x 1(first shell)2 or 2 electrons. The second shell can have up to 2 x 2(second shell)2 or 8 electrons. The third shell can have up to 2x32 or 18 electrons. The fourth shell can have up to 2x42 or 32 electrons. All the way up to the seventh shell which can have 2x72 or 98 electrons! One last thing about shells, the shells have to be full before the electrons will go to the next shell. A helium atom will have two electrons. Both of them will be in the first shell. A Lithium atom will have three electrons. Two will be in the first shell and one (since the first shell is filled) will be in the second shell.


Electron Sharing

Electrons provide the size and stability of the atom and, as such, the mass and the structure of all matter. Electrons are also the key to all electromagnetic energy. But wait, that’s not all! It is the number of electrons in an atom that determines if and how atoms come together to form molecules. Electrons determine how and what matter will be.

Atoms like to feel satisfied and they feel satisfied if they are “full”. An atom is full if it eats four hot dogs and a large fry. Just kidding. An atom is “full” if its outer electron shell has as many electrons as it can hold or if there are eight or a multiple of eight (16, 24 etc.) electrons in the outer shell. This is called the octet rule and works most of the time, but is not perfect.

If an atom is not full, it is not satisfied. An unsatisfied atom needs to do something with its electrons to be happy. Luckily atoms are very friendly and love to share. Most atoms are not satisfied as individuals. The oxygen atom below has six electrons in its outer shell. It needs eight electrons to be satisfied. Luckily, two Hydrogen atoms happen by. Each one of them has only one electron in its outer shell and needs one more to be satisfied. If both Hydrogens share their one electron with the Oxygen, the oxygen has eight electrons and is satisfied. Also, if the Oxygen shares an electron with each Hydrogen, then both Hydrogens are satisfied as well. Just like your mother told you, it’s nice to share. It is this sharing of electrons that makes atoms come together to form molecules.

Experiment 1


This is the most complicated and difficult experiment I have ever given. You don’t need to do this to get the concepts of this lesson but it’s such a neat and classical experiment (my students love it) that I’m going to write it up for you so you can give it a try. The reason I like this is because what you are really doing in this experiment is ripping molecules apart and then later crashing them back together. You are destroying and then creating water with your bare hands (and some electricity)! Have fun and please follow the directions carefully. This could be dangerous if you’re not careful.


You need:

1 test tube or thin glass or plastic something closed at one end. I do not recommend anything wider than a half inch in diameter.

2 two wires, one needs to be copper, at least 12 inches long. Both wires need to have bare ends.

1 Cup


1 9 volt battery

Long match or a long thin piece of wood (like a popsicle stick) and a match

Rubber bands

Masking tape


1. Fill the cup with water.

2. Put a tablespoon or so of salt into the water and stir it up. (The salt allows the electricity to flow better through the water.)

2. Put one wire into the test tube and rubber band it to the test tube so that it won’t come out (see picture).

3. Use the masking tape to attach both wires to the battery. Make sure the wire that is in the test tube is connected to the negative (-) pole of the battery and that the other is connected to the positive (+) pole. Don’t let the bare parts of the different wires touch. They could get very hot if they do.

4. Fill the test tube to the brim with the salt water.

5. This is the tricky part. Put your finger over the test tube, turn it over and put the test tube, open side down, into the cup of water. (See picture.)

6. Now put the other wire into the water. Be careful not to let the bare parts of the wires touch.

7. You should see bubbles rising into the test tube. If you don’t see bubbles, check the other wire. If bubbles are coming from the other wire either switch the wires on the battery connections or put the wire that is bubbling into the test tube and remove the other. If you see no bubbles check the connections on the battery.

8. When the test tube is half full of gas (half empty of salt water depending on how you look at it) light the long match or the wooden stick. Then take the test tube out of the water and let the water drain out. Holding the test tube with the open end down, wait for five seconds and put the burning stick deep into the test tube (the flame will probably go out but that’s okay). You should hear an instant pop and see a flash of light. If you don’t, light the stick again and try it another time. For some reason, it rarely works the first time but usually does the second or third.

What you have done is ripped the molecules of water apart and then crashed them back together. A water molecule, as you saw before, is two hydrogen atoms and one oxygen atom. The electricity encouraged the oxygen to react with the copper wire leaving the hydrogen atoms with no oxygen atom to hang onto. The bubbles you saw were caused by the newly released hydrogen atoms floating through the test tube in the form of hydrogen gas. Eventually that test tube was part way filled with nothing but pure hydrogen gas. When you put the match to it, the energy of the heat causes the hydrogen to react with the oxygen in the air and “POP”, hydrogen and oxygen combine to form what? That’s right, more water. You have destroyed and created water! (It’s a very small amount of water so you probably won’t see much change in the test tube.) Don’t you feel powerful!


Electrons don’t orbit nuclei. They pop in and pop out of existence.

Electrons do tend to stay at a certain distance from a nucleus. This area that the electron tends to stay in is called a shell.

The electrons move so fast around the shell that the shell forms a balloon like ball around the nucleus.

An atom can have as many as seven shells.

The number of electrons an atom has determines how many shells it has.

A shell can only hold so many electrons. The number of electrons a shell can hold can be determined by the formula 2n2 where n is the number of the shell.

Atoms are “satisfied” if they have a full outer shell or if they have a multiple of eight electrons in their outer shell.

If an atom is not “satisfied” it will gladly share electrons with other atoms forming molecules.



1. How do electrons move?

2. Do electrons just go all over the place in an atom?

3. What is a shell?

4. How many shells can an atom have?

5. What determines how many shells an atom has?

6. How many electrons can be in the third shell of an atom?

7. How many shells does a Sodium atom have? Sodium has 11 electrons.

8. Why do atoms come together to form molecules?




1. They pop in and out of existence.

2. No. They tend to stay a certain distance away from the nucleus.

3. A shell is the distance that electrons tend to stay in as they pop around the nucleus.

4. Up to seven.

5. The number of electrons an atom has.

6. 18. Remember 2n2. So 2 x 32 = 18.

7. 2 atoms fill the first shell, 8 fill the second, and 1 is left in the third. So Sodium has 3 shells.

8. Because they are “unsatisfied’. They have too many or not enough electrons in their outer shell. By sharing

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