Frostbite Theater

Announcer: Frostbite Theater presents... Cold Cuts! No baloney!

Joanna and Steve: Just science!

Joanna: Hi! I'm Joanna!

Steve: And I'm Steve!

Joanna: Today, we're going to show you how to draw an atom!

Steve: In addition to paper and pencils and crayons and markers or whatever you're going to use to make the drawing, you're going to need a copy of the Periodic Table of Elements.

You can download one from our site, or use one of the thousands of others you can find online.

Joanna: Once you have one, it's time to pick an element.

Since we use it all the time, we're going to pick nitrogen.

Steve: In general, atoms contain protons, neutrons and electrons. So, how many protons, neutrons and electrons are in an atom of nitrogen?

Joanna: We can tell from the Table of Elements. Let's take a close look at nitrogen.

See the number in the upper corner? That number is called the atomic number. It tells us how many protons are in an atom of an element.

Nitrogen's atomic number is seven. That means every atom of nitrogen has exactly seven protons.

Steve: You might notice that the atomic number is different for every element. Every element contains a unique number of protons.

If an atom contains exactly three protons, then its an atom of Lithium.

If an atom contains exactly 79 protons, then its an atom of gold.

If you want to know which element an atom is, count the protons.

Joanna: Now that we know that an atom of nitrogen has seven protons, finding the number of electrons is easy.

Overall, atoms are electrically neutral. Protons, though, carry a positive electrical charge. How can an atom of nitrogen be neutral if it contains seven positively charged protons?

Because electrons carry a charge that's equal in size to the proton's, but opposite in sign.

If an atom of nitrogen is neutral and it contains seven positively charged protons, then it must contain seven negatively charged electrons.

In short, for an atom, the number of electrons is also equal to the number of protons.

Steve: So, what about the neutrons? Determining the number of neutrons can be a little tricky because atoms of the same element can have different numbers of neutrons. These different versions of an element are called isotopes and different isotopes have different masses.

That's part of the reason why this number, which is called the atomic weight, looks so messy. It's taking into account how much of each isotope typically exists in nature.

Joanna: So, what do you typically do with messy numbers? You round them. Rounding the atomic weight to the nearest whole number gives us something called a mass number, and the mass number identifies a specific isotope of an element.

If you've ever heard of carbon-14 or lead-210, then you've seen mass numbers in use before.

Steve: The mass number tells us the total number of protons and neutrons in an atom. When we round nitrogen's atomic weight, we get 14, so we know our drawing is going to have a total of 14 protons and neutrons. But, we already know that every atom of nitrogen has exactly seven protons. So, if our atom needs a total of 14 protons and neutrons, and it must have exactly seven protons, then the remaining seven particles are neutrons.

In short, the number of neutrons is equal to the mass number minus the atomic number.

Joanna: Now that we know how many protons, neutrons and electrons we're going to draw, what goes where?

The protons and neutrons go in the middle of the atom. This is called the nucleus, and it's where most of an atom's mass is located.

Steve: The electrons go outside the nucleus, but how you place them depends on which model of the atom you're following.

I mean, depending on the purpose of your drawing, it might be good enough to randomly plunk the electrons around the nucleus and call it a day.

We're going to be a little more sophisticated, though, and follow the Bohr model.

Joanna: In the Bohr model, the electrons can't be anywhere they want to be. They can only be in certain energy levels or shells. In addition, only a certain number of electrons can go in each shell. The first shell can hold two electrons and the second shell can hold eight.

So, we'll draw two of nitrogen's electrons in the first shell and place the remaining five electrons in the second.

Steve: If you're drawing a larger atom, you'll need to be a little careful with this. Higher energy levels can start to fill before the lower ones run out of room. Checking an element's electron configuration table will tell you exactly how many electrons there are in each level.

Joanna: So, that's about it for our drawing. I hope you like it!

Keep in mind that this is just a model. It isn't perfect.

The biggest problem is that our electrons are too close to the nucleus.

If the nucleus were the size of your fist, the electrons wouldn't be in the same room as you.

They wouldn't even be in the same building.

They'd be at least a kilometer or two away.

Steve: And a drawing that size would never fit on your refrigerator...

Joanna: Nope.

Thanks for watching!

I hope you'll join us again soon for another experiment!

Poof! You're a dinosaur!

Steve: Raaaaaaarh!