Why is helium in group 18 if it is an s-block element?
Helium’s configuration is 1s² — two electrons in an s orbital, and nothing else. By the rule that block follows the subshell being filled, helium is an s-block element, and it should sit above beryllium in group 2.
It does not, and the reason is that group placement in the periodic table follows chemistry, not bookkeeping. Helium’s outer shell is full. The n = 1 shell holds only two electrons, so 1s² is a closed shell in the same sense that neon’s 2s² 2p⁶ is. Helium is chemically inert, monatomic and unreactive — the defining behaviour of group 18, and nothing at all like beryllium.
This page colours helium as s block and places it in group 18, which looks inconsistent until you notice it is reporting two different true facts. The block describes where the last electron went. The group describes how the element behaves. For every element except helium these agree.
A minority of chemists argue helium should be moved to group 2 for consistency, and left-step periodic tables do exactly that. The argument has never won, because a table that separates helium from the other noble gases would obscure the strongest chemical family resemblance in the whole system.
How was helium discovered in the Sun before Earth?
In 1868, during a total solar eclipse visible from India, Pierre Janssen observed a bright yellow line in the spectrum of the solar chromosphere at a wavelength of about 587.6 nm. Norman Lockyer, working independently in England, saw the same line and concluded it belonged to an element not known on Earth. He named it after Helios.
The claim was treated with scepticism for decades. It was only in 1895 that William Ramsay, treating the uranium mineral cleveite with acid, collected a gas whose spectrum matched Janssen’s line exactly.
The 27-year gap is not a curiosity. It is the first time an element was identified somewhere other than Earth, and it established spectroscopy as a tool that could survey matter across astronomical distances. Everything we know about the composition of stars and galaxies descends from that method.
Helium turned out to be the second most abundant element in the universe, at roughly 24% of ordinary matter by mass, almost all of it produced in the first few minutes after the Big Bang. It is scarce on Earth for a specific reason: it is light enough to escape the atmosphere entirely, and it does not bond to anything that would hold it down.
Why does helium have the lowest boiling point of any element?
Helium boils at 4.22 K — about −269 °C. No other substance stays liquid to a lower temperature.
Two properties combine to produce that. First, helium atoms have no dipole and no unpaired electrons, so the only force between them is London dispersion, the weakest of all intermolecular attractions. Second, helium’s electron cloud is small and tightly held, which makes it barely polarisable, so even dispersion forces are unusually feeble.
The result is a liquid held together by almost nothing. Very little thermal energy is needed to pull the atoms apart, so the boiling point sits just four degrees above absolute zero.
The same weakness produces something stranger. Cool liquid helium below 2.17 K — the lambda point — and it becomes a superfluid: it flows with zero viscosity, climbs the walls of its container in a thin film, and conducts heat so efficiently that it stops bubbling entirely. Superfluidity is a quantum effect made visible at human scale, and helium is the only element that shows it under ordinary laboratory conditions.
Helium also refuses to freeze. At atmospheric pressure it stays liquid all the way to absolute zero. Quantum zero-point motion — the residual jiggling that the uncertainty principle forbids from stopping — is enough to prevent a lattice from forming. Solid helium requires roughly 25 atmospheres.
What is helium used for, and why does the supply matter?
The obvious use, filling balloons, is the least important one. Helium’s real value is in what nothing else can do.
Liquid helium is the only practical coolant for superconducting magnets, which means it is the working fluid inside every MRI scanner and the Large Hadron Collider. Its inertness makes it the shielding gas for arc welding of reactive metals and the carrier gas in gas chromatography. Its small atomic size makes it the standard tracer for leak detection in vacuum systems.
The supply problem is structural. Helium on Earth is almost entirely radiogenic: alpha particles emitted by decaying uranium and thorium in the crust, captured in the same geological traps that hold natural gas. It accumulates over hundreds of millions of years and is extracted as a by-product of gas production.
Once released, it is gone. Helium is too light for Earth’s gravity to retain, so atmospheric helium drifts to the top and escapes to space. Every other element we use stays on the planet in some form and can in principle be recovered. A balloon released at a birthday party removes its helium from the accessible world permanently.
Why is helium the second most abundant element in the universe?
Helium accounts for roughly 24% of ordinary matter by mass, and hydrogen for most of the remainder. Everything else — carbon, oxygen, iron, gold — makes up about 2% between them.
Nearly all of that helium was made in the first few minutes after the Big Bang, in a process called Big Bang nucleosynthesis. The early universe was hot enough for protons and neutrons to fuse, and the ratio of the two at the moment fusion became possible determined how much helium formed. Essentially every available neutron ended up locked inside a helium-4 nucleus, which is exceptionally stable.
Fusion then stopped, because there is no stable nucleus with mass number 5 or 8. The chain from helium to heavier elements has a gap in it, and the universe cooled and thinned too fast to bridge it. Stars later solved the problem with the triple-alpha process, fusing three helium nuclei almost simultaneously — but that takes stellar densities and millions of years.
The predicted primordial helium fraction of about 24% matches observation closely, and it is one of the strongest pieces of evidence for the Big Bang model. A universe that had always existed in its current state would have no reason to contain that particular amount.