Helium: More Than Just Party Balloons
The Fundamental Properties of Helium
Helium is a chemical element with the atomic number 2. This means every atom of helium has two protons in its nucleus. It's a member of the noble gas family on the periodic table, which are all gases known for being very stable and not reacting easily with other elements.
Chemical Symbol: He
Atomic Number: 2
State at Room Temperature: Gas
Density: 0.1786 grams per liter (Air is about 1.225 grams per liter)
Boiling Point: -268.9 °C (-452.0 °F) – just a few degrees above absolute zero!
The most famous property of helium is its low density. Density is a measure of how much mass is packed into a certain volume. Think of it like this: a kilogram of feathers and a kilogram of lead have the same mass, but the feathers take up much more space—they are less dense. Helium atoms are very small and light, so a balloon-sized volume of helium weighs much less than the same volume of air. This difference in density creates an upward force called buoyancy.
Why does a helium balloon float but a balloon you blow up with your breath sinks? The air we exhale is mostly nitrogen and oxygen, which are heavier than the mixture of gases in the surrounding air. A helium balloon, being lighter, is pushed upwards by the heavier air around it, just like a cork pushed up through water.
Where Does Helium Come From?
Helium has a cosmic origin. It was first formed during the Big Bang and is continuously created in the cores of stars through nuclear fusion, where hydrogen atoms fuse together. On Earth, however, helium is not mined from the air because it's too diffuse. Instead, it is found underground, trapped in natural gas reservoirs.
Most of the world's helium supply comes from the radioactive decay of heavy elements like uranium and thorium deep within the Earth's crust. As these elements break down over millions of years, they emit alpha particles, which are essentially the nuclei of helium atoms (He^(2+)). These particles slow down and attract two electrons, becoming stable helium gas. This gas then gets trapped alongside natural gas, and it is separated and purified during natural gas extraction.
| Gas | Chemical Formula | Density (g/L) | Behavior in Air |
|---|---|---|---|
| Helium | He | 0.1786 | Rises rapidly |
| Hydrogen | H$_2$ | 0.0899 | Rises rapidly (highly flammable) |
| Methane | CH$_4$ | 0.656 | Rises |
| Air (Average) | N$_2$, O$_2$, etc. | 1.225 | Neutral (reference point) |
| Carbon Dioxide | CO$_2$ | 1.842 | Sinks |
Helium in Action: From Parties to High-Tech
The most visible use of helium is in filling party balloons and large blimps. But its unique properties make it indispensable in many scientific, medical, and industrial fields.
Cooling Supermagnets: Helium has the lowest boiling point of any element. When liquefied, it becomes a cryogenic fluid capable of reaching temperatures close to absolute zero (-273 °C). At these temperatures, certain metals lose all electrical resistance, becoming superconductors. The powerful magnets in Magnetic Resonance Imaging (MRI) machines in hospitals rely on these superconductors, which must be cooled by liquid helium to function. Without helium, modern medical diagnostics would be vastly different.
Shielding Gas for Welding: In high-precision welding, especially of metals like aluminum and stainless steel, helium is used as a shielding gas. It creates an inert atmosphere that prevents the hot, molten metal from reacting with oxygen and nitrogen in the air, which would cause a weak, brittle weld.
Pressurizing and Purging: Helium is used to pressurize the fuel tanks of large rockets because it remains a gas even at the extremely low temperatures of liquid hydrogen and oxygen fuel. It is also used to purge systems of other gases because its small, monatomic molecules can find even the tiniest leaks, a critical step in ensuring the safety of pipelines and spacecraft.
Breathing Mixtures: Deep-sea divers breathe a mixture of helium and oxygen (called heliox). Normal air (nitrogen and oxygen) becomes toxic under high pressure at great depths, causing a condition known as nitrogen narcosis. Helium, being inert, does not cause this effect and is easier to breathe under pressure.
Common Mistakes and Important Questions
Why don't we use hydrogen in balloons since it's even lighter than helium?
Why does a helium balloon eventually fall down?
Is there a helium shortage?
Footnote
1 MRI: Magnetic Resonance Imaging. A medical imaging technique used to form detailed pictures of the organs and tissues in the body.
2 Noble Gas: Any of the seven chemical elements that make up Group 18 of the periodic table. They are generally odorless, colorless, and have very low chemical reactivity.
3 Buoyancy: An upward force exerted by a fluid (like air or water) that opposes the weight of an immersed object. If the buoyant force is greater than the object's weight, the object will float.
4 Cryogenic: Relating to the production and behavior of materials at very low temperatures, typically below -150 °C (-238 °F).