That Sinking Feeling

Helium-filled balloons are lots of fun because the balloon lifts up into the air. But they don't last long. Within a day or two, they begin to sink lower and lower, and to get smaller and smaller. Why does this happen?

This is an example of a process known as effusion. Effusion occurs when gas molecules are able to escape their container through a little hole. All gas molecules, whether they're heliums in the balloon, or nitrogens, oxygens, or something else in the air, are moving around really fast (around 1000 miles per hour!!). Every now and then, one of them finds a hole and gets out. Understand that these are very, very tiny holes - too small for you to see. Helium atoms are much smaller than molecules like nitrogen, oxygen, or carbon dioxide, so it's a lot easier for them to get out the hole. They also move faster, so they find the holes more quickly.

You might try some experiments with effusion. Get two helium-filled balloons - one rubber and one Mylar (the shiny kind). Do they both lose helium at the same rate? Compare a helium-filled balloon to one inflated with air or your breath (which has more carbon dioxide than the air you breathed in). Can you see the difference in gas effusion?

Common Scents Molecules

Here's an observation game for you to play with some molecular structures from very smelly molecules (that can be a good thing or a very BAD thing)!

Here's the first set! (C means carbon, H means hydrogen, S means sulfur):

Do molecules that contain sulfur seem to smell nice? Of course, these are only a few of the millions of molecules that can contain sulfur, but frankly, most of them are pretty stinky!

Now look at the second group! (C means carbon, H means hydrogen, N means nitrogen):

Whoa! These are worse than the sulfur-containing molecules! In fact, most of the world's very worst-smelling molecules contain nitrogen. There's even one called "putrescene"! However, there are also many, many perfectly odor-free nitrogen-containing molecules!

Let's do some nicer-smelling examples (C means carbon, H means hydrogen, O means oxygen):

Now we're talking! These are odors that we don't mind sniffing! What features do you observe in common? See that group with an O next to a =O? The atom without a label is a carbon. That's called an ester group, and esters tend to have sweet, pleasant odors. Find the ester group in each molecule.

More nice molecules:

These are a group of molecules called terpenes. They have that hexagon thing at the top (which is sometimes broken, with only 5 carbons), and that funny fishtail part at the bottom. Terpenes tend to have sharp, but pleasant, odors. Notice that there are different things hanging off the rin in different places, and these are what make each molecule smell different.

Here's the last set! (C means carbon, H means hydrogen, O means oxygen):

All of these molecules are aldehydes, because they all have the HC=O part. See if you can find this aldehyde group in each example.

Now, please understand that natural scents usually have lots of molecules in them, not just one. However, in all of these examples, if you smelled this molecule, you would know immediately what it came from. The smell wouldn't be exactly like the natural scent, but you could recognize it.

One final comment - earlier this month, we talked about how the receptors in the nose reacted with the odor molecules, letting you smell them? Well, these are examples of those odor molecules. Now here's the cool thing - your nose's receptors can tell that these molecules have different sizes and shapes, and that's how you can tell smells apart! The receptors send slightly different signals to your brain, which knows that you should identify one kind of signal with bananas, and another kind with poop! And that's a very good thing!

Goal!

So how do those scent molecules get through the air to your nose? They do this by a process called diffusion. The nitrogen, oxygen, carbon dioxide, and other molecules in the air are moving around very fast (about 1000 miles per hour, even faster than a jet airplane!) When a scent molecules gets into the air, the molecules in air begin to hit the scent molecules, kicking it around like a soccer ball. Sooner or later, they kick it into your nose! Now, your nose probably can't smell just one scent molecule, but there are gazillions of air soccer players kicking around billions of scent molecules, so eventually a lot of them get to your nose. Not surprisingly, the farther away your nose is, the longer it takes to smell something. Also, the colder it is, the slower all the molecules move. And the bigger the scent molecule, the longer it takes to smell (usually).

Here's a way you can observe diffusion in action. Line up about 5 or 6 family members or friends in a row, each about 2-3 feet apart. You can do this in a large room, down a hall, or outside. Have them all face away from you and close their eyes. Tell each person to raise a hand when he or she smells something. Open a bottle of something smelly, like mouthwash, perfume, or rubbing alcohol. Turn around and look for raised hands. You will probably see that the people closest to you raise their hands quickly, but that it takes longer for the people farther away. Some may never smell it at all (especially if you're outside on a windy day). Try the same experiment with different kinds of smells and with more people!

Fun Facts 9

Many of the artificially created elements are named after famous scientists, such as:

• Curium (Cm, #96) honors both Marie and Pierre Curie, who discovered several naturally occurring radioactive elements (Ra, Rn, and Po). They both won Nobel Prizes for physics in 1903, and Marie won the chemistry prize alone in 1911. Their daughter, Irene Joliot-Curie, also won for chemistry in 1935, making Marie and Irene the only mother-daughter pair to win Nobels!
• Fermium (Fm, #100) honors Enrico Fermi, an Italian physicist who carried out the world's first nuclear chain reaction, in a room underneath the football stadium at the University of Chicago!
• Seaborgium (Sg, #106) honors Glenn Seaborg, an American chemist who discovered many new elements
• Meitnerium (Mt, #109) honors Lise Meitner, an Austrian physicist who discovered how radioactive nuclei fall apart. She never won the Nobel Prize, which many people believe was not fair.
• Roentgenium (Rg, #112) honors Wilhelm Roentgen, a German physicist who discovered X-rays.

Now back to our random collection of elemental trivia:

• When automobile airbags inflate, they fill with nitrogen (N, #7) gas created by a reaction that is triggered by shock. This takes up a lot less space than putting a container of gas under the hood of the car!
• Camera flashes are usually filled with krypton (Kr, #36) gas, which glows bright white when an electrical current is passed through it.
• Thulium (Tm, #69) has a reputation as one of the least interesting elements because it doesn't have any special properties. It is used to make lasers.
• Some rock formations give off radioactive radon (Rn, #86) gas. Buildings constructed on these formations may build up dangerous levels of radon in the air, and must be well-ventilated.
• Thallium (Tl, #81) compounds have been used to kill insects and other pests. But they are so poisonous that they're now illegal in many places.
• If a little germanium (Ge, #32) is added to sterling silver, the metal does not tarnish so fast.