What is Radon? - Definition, Facts & Effects

Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

A noble gas that is radioactive and a leading cause of lung cancer, radon is a gas to be on the lookout for. Want to understand how to spot radon? Continue reading to learn about radon, its facts, and effects.

All Things Radon Defined

Did you know that, under certain laboratory conditions, you can observe a green halo floating around radon? It is certainly possible. Radon is a chemical element that is identified as a type of gas. You can't miss spotting radon on the periodic table. It is a noble gas found on the right side of the periodic table, hanging with all the other noble gases. Diagram 1 shows what radon looks like on the periodic table.

Diagram 1: Radon As Shown On The Periodic Table

Now, why would chemists give radon the title of 'noble'? Well, in chemistry radon is considered to be chemically inactive. This just means it would rather stay to itself than hang with other chemical elements. The rumor out there is that this type of behavior was considered to be 'noble,' hence the category, noble gas. Whether or not this is true, it sure does sound interesting.

The concept of radioactivity was first discovered in 1896 by French physicist Antoine-Henri Becquerel. It wasn't until 1900 that German physicist Friedrich Ernst Dorn further developed this concept by discovering that an element named radium could become radioactive when interacting with air. Even more, he learned that this element could break apart and form a gas later called radon.

Radon was given its name because of its radioactive nature. This name is fitting as it was first detected that radon-222 was emitted from another element on the periodic table, radium. Some other tidbits of information about radon worth mentioning are that its atomic number is 86, its symbol is Rn, and the atomic mass for radon is 222g/mol. All of this is shown in Diagram 1 (if you haven't spotted it already). Now that we have some background information on radon, let's look at some important facts regarding this gas.

Key Facts About Radon

There are many things to keep in mind when you encounter radon. The following facts are important and certainly worth understanding more in-depth:

Fact #1: Radon is a radioactive element. Besides being a noble gas, radon is radioactive. This means that radon not only likes to stay by itself but also loves giving off radioactive waves wherever it goes. It also means that radon likes to break down into other elements like lead. It took many years to figure out that radon was radioactive.

Fact #2: Radon has different physical properties. Radon doesn't have a very impressive look. It's considered to be a gas that is tasteless, colorless, and odorless.

Fact #3: Radon loves hanging around. Heavier than air, never forget that radon is one heavy gas and likes to linger around (low to the ground) in the environment. With a density of 9.73 kg/m3 and the density of air being 1.225 kg/m3, it makes perfect sense that this gas is so heavy. We will discuss this further in the effects section of this lesson.

Fact #4: Radon can emit a colorful halo. Although as a gas radon is colorless, it can fool you with its color style. Below a certain freezing point, radon can change states from a gas to a solid. This will also cause radon to change colors from yellow to red. Believe it or not, I wasn't kidding about radon's halo. This color change actually contributes to the bright glow it can give off.

Fact #5: Radon is found everywhere. It's mostly abundant in the air, but don't be surprised if you hear about radon hanging out in groundwater or even in natural hot springs. Professionals can detect radon's presence by using devices and detectors specifically designed to identify if radon is present or not. However, the takeaway is that radon is widely identified throughout our environment.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account