1. Look up, it’s helium!

Helium (He) is at the top of Group 0 on the Periodic Table

Helium sits high and mighty in group 0 of the Periodic Table, above all other noble gases. And in real life, helium floats high up, lifting party balloons or the military airship that watches over Singapore’s airspace.

The sun’s corona during a solar eclipse (photo from NASA)

Incidentally, looking high up into space hinted astronomers about the existence of helium previously unknown to humans.

It was 18 August 1868. The sky over India dimmed momentarily during a total solar eclipse, giving way to the sun’s corona. French astronomer Pierre Janssen took the chance to gaze at the sun through his special telescope, analysing the colours of light shed by the corona. He compared them to the colours elements give off during the flame test. Some matched those of hydrogen. But there were also unexplained colours with no corresponding element.

Janssen could doubt his observations. But he was creative (and maybe cocky) enough to stick by it and suggest that it was due to a yet undiscovered element. Finally, after three long decades, he was proven right by an Italian scientist who found helium in the lava from Mount Vesuvius.

So yes, we discovered helium on the sun first. And we named it after the Greek word for sun helios.

2. Helium reacts with nothing on its way up

Chemistry explains why helium was hiding so well away from us.

Like all other noble gases, helium is extremely unreactive. We can also use a cheem phrase to describe it: chemically inert. This means that it does not normally mingle and react with other elements.

Left on its own, helium is less dense than air. Without anchoring itself to another element, it rises up into the sky and eventually escapes into space. Therefore, the atmosphere only contains a trace amount of helium, so little that it cannot be isolated and identified directly from air.

In contrast, while hydrogen is even less dense and lighter than helium, it can react with other elements to become locked in heavy compounds like acids and hydrocarbons.

All noble gases are generally unreactive. They do not usually form compounds.

3. Helium and other noble gases are monatomic elements

Not only do noble gases shun other elements, but also atoms of their own kind.

So in a helium balloon are discrete, isolated atoms with no covalent bond between each other. Therefore, we can describe helium as a monatomic gas.

This stands in contrast to gases from other groups. For example, hydrogen from Group I exists as hydrogen molecules consisting of two hydrogen atoms each.

Noble gases are monatomic elements.

4. Noble gases have stable electronic structures

To explain why helium and all other noble gases are generally unreactive and monatomic, we have to consider their electronic structures.

Atoms of group 0 have complete outer shell. For helium, its outer shell is the first shell, which is complete with just 2 electrons. For the vast majority of noble gases below helium, they instead have 8 electrons in their complete shell.

The complete outer shell is stable. Gaining, losing or sharing electrons reduces this stability. Therefore, atoms of noble gases do not form any bond under most circumstances.

Noble gases are unreactive because their atoms have complete outer shell. Therefore, they tend not to gain, lose or share electrons.

5. Mighty noble gases protect

Since helium is unreactive and by extension not flammable, it keeps our party balloons and airships safe. It saves us from a repeat of the Hindenburg disaster in 1937, whereby a hydrogen-filled zeppelin came down in flames.

Similarly, neon and argon provide an inert atmosphere in light bulbs. This prevents the metal filament from burning away.

Metal welding (photo from Air Source Industry)

Argon is also used in steelmaking and metal welding to prevent liquid metal from oxidising.