Helium (He)

Helium (He) is element 2 — second slot on the periodic table.

Basics

• Atomic number: 2 (2 protons)

• Molecular form: monatomic (He itself is the chemical unit)

• State: colorless, odorless gas at room temp

• Density: ~1/7 of air — that's why balloons float

• Boiling point: -268.9°C — the lowest of any element

• Melting point: practically doesn't exist. At 1 atm, no liquid→solid transition. Only solidifies above ~25 atm

Noble Gas — Chemistry's Lazy Friend

Helium's defining trait: it barely bonds with anything.

For an atom to be stable, its outer electron shell needs to be "full." Helium already fills its first shell with 2 electrons — nothing to gain or give. So it forms almost no compounds.

A handful of helium compounds have been synthesized in extreme cryo/high-pressure labs, but you'll never encounter one in daily life.

Classic example of "monatomic molecule" from the earlier post — one atom acting as a complete chemical unit.

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#2 Most Abundant in the Universe

About 24% of the universe's mass is helium. Hydrogen is #1 (74%). Together that's 98%. Every other element on Earth fits in the remaining 2%.

This ratio was set during Big Bang nucleosynthesis. In the ~3 minutes after the Big Bang, as the universe cooled, protons and neutrons fused into hydrogen (75%) + helium (25%) + trace lithium. All the elements stars made later (carbon, oxygen, iron...) account for under 2% of total mass.

Helium is a fossil of the Big Bang. The atoms in your party balloon were made 13.8 billion years ago as the universe cooled.

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But It's Rare on Earth — Why?

Here's the paradox. Plentiful in the universe, but only 0.0005% of Earth's atmosphere.

Reason: too light. Helium atoms move so fast that Earth's gravity can't hold them. They constantly escape from the upper atmosphere into space.

So where does our helium come from?

Natural Gas Byproduct

Earth's helium mostly comes from radioactive decay of uranium and thorium in rock. Alpha particles are literally helium nuclei (He-4 = 2 protons + 2 neutrons), so every alpha decay produces one helium atom.

This helium gets trapped in underground gas pockets and comes up as a byproduct of natural gas extraction. Natural gas typically contains 0.1-7% helium, which is separated and recovered.

Major producers: USA (especially Texas, Kansas), Qatar, Algeria, Russia. The US once produced 70% of the world's helium.

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The Depletion Crisis — Once Released, Gone Forever

Here's the real problem. Helium is one of the very few resources that can't be recovered once released.

• Balloon pops, MRI leaks → upper atmosphere → space → permanently lost

• Reserves are finite, replenishment depends on radioactive decay (extremely slow)

• US Congress's 1996 "Helium Privatization Act" kept prices artificially low for decades — helium got cheap enough to use in party balloons → industry and science worried

Scientists keep saying "don't put helium in balloons" for this reason. Every balloon = permanent loss, and there's no substitute for MRI or semiconductor processes.

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Industrial Uses

1. MRI / NMR (Biggest Use)

Hospital MRI machines use superconducting magnets. Superconductivity (zero electrical resistance) requires liquid helium (-269°C) cooling.

No helium, no MRI. That's why every helium price spike hits hospitals hard.

2. Semiconductor / Optical Fiber Manufacturing

Used as inert atmosphere for wafer processing. Essential for optical fiber drawing too.

3. Deep Diving (Trimix)

For deep dives (50m+), divers use Trimix — helium + oxygen + nitrogen instead of air. Too much nitrogen at depth causes nitrogen narcosis and decompression sickness. Helium has weaker narcotic effect and lower bends risk.

4. Airships

After the Hindenburg disaster (1937, hydrogen), all modern airships use helium. No explosion risk. Drawback: expensive.

5. NASA Rockets

NASA uses ~10% of US helium for pressurizing fuel tanks, purging gases in spacecraft — needs an inert gas that won't react.

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Inhaling Helium → Funny Voice (And Danger)

Breathing helium from a balloon makes your voice sound "Mickey Mouse."

Reason: sound travels ~3× faster in helium than air (343 m/s in air vs 1007 m/s in helium). Your vocal cords vibrate the same, but resonance frequencies in the helium-filled vocal tract shift up, changing the timbre.

Risks:

• Helium itself is non-toxic (inert)

• But helium displaces air in your lungs → oxygen deprivation (asphyxiation) risk

• Party balloon helium is usually mixed with air, so a single breath isn't immediately dangerous — but pure industrial helium can knock you out in one breath

• Fatalities have occurred. Don't "just try one breath."

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Liquid Helium and Superfluidity

Cool helium to -269°C and it liquefies. Cool it further below -271°C (the lambda point) and it becomes a superfluid.

Superfluid = zero viscosity. It climbs cup walls and flows out — quantum mechanics manifesting at macroscopic scale. One of the few visible windows into quantum behavior.

Fascinating, but limited practical use (mostly low-temperature physics research).

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Helium-3 — Future Energy Scenario

Two helium isotopes:

• Helium-4 (2 protons + 2 neutrons): almost all the helium we use daily

• Helium-3 (2 protons + 1 neutron): extremely rare

Helium-3 is a candidate fusion fuel. D + He-3 fusion produces almost no neutrons — called "clean fusion."

Problem: barely any He-3 on Earth. The Moon's surface has accumulated solar-wind He-3 over billions of years, supposedly in significant quantities. That's why some space programs (China, India) cite "He-3 mining on the Moon" as motivation.

Fusion isn't commercialized yet, and D-He3 is much harder than D-T fusion. Not a near-term scenario.

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Summary

Aspect	Note
Universe mass fraction	24% (#2 after hydrogen)
Earth atmosphere fraction	0.0005% (very rare)
Earth origin	Radioactive decay (slow)
Source	Natural gas byproduct
Most important use	Cooling MRI superconducting magnets
Future wildcard	He-3 fusion (lunar mining)
Concern	Once released, unrecoverable. Finite reserves

"For MRI, not balloons." Worth a thought next time you see a helium balloon.