Prominent among non-believers was a rather formidable opponent, Dmitrii Mendeleev. The Russian chemist was no stranger to hostility and derision, having been on the receiving end for more than half a decade following his publication of his periodic table.
But for Mendeleev, spectacular vindication of his discovery came in , when — using a spectroscope — Paul-Emile Lecoq de Boisbaudran discovered gallium, an element whose atomic weight fitted perfectly in a gap in the table.
The discoveries of scandium and germanium soon afterward plugged further holes. But none of these aided the case for helium, because the periodic table of the time had no gap for helium to fill.
It was an omission that would come back to haunt Mendeleev. In , English chemist William Ramsay discovered an unreactive gas, which he named argon, released by heating a sample of a mineral. Unsure what to make of this new element that his periodic table had not predicted, Mendeleev argued Ramsay had not discovered a new element at all, but a previously unobserved three-atom molecule of nitrogen akin to ozone O 3.
But in , repeating the heating experiment with a uranium mineral, Ramsay isolated another inert gas. This one produced a spectral line that was an exact match for those Janssen and Lockyer had observed in the Sun. Ramsay had found helium on Earth. Ramsay soon went on to discover krypton, neon and xenon — all remarkably unreactive.
The completed new set of elements convinced Mendeleev that the periodic table needed expanding. The noble gases, headed by helium, now sit on the far right hand side of the table, a position that reflects their neatly filled outer shell of electrons. It was no lucky accident that Ramsay isolated helium from a uranium-rich mineral. It is the slow decay of radioactive uranium and thorium nuclei that is the main source of helium on the planet today. Several uranium and thorium isotopes decay by emitting alpha particles — a little cluster of subatomic particles consisting of two protons and two neutrons.
This combination of subatomic particles is the very set that makes up the helium nucleus. Across the universe, helium is the second most common element after hydrogen. Most of this helium originates from a brief period a couple of minutes after the Big Bang, when temperatures cooled enough for small clusters of subatomic particles to form the first atomic nuclei. Some , years later , the universe finally cooled enough for these nuclei to capture electrons, forming the first atoms — mainly hydrogen and helium, which still dominate the universe today.
Being inert, it is not held down by chemistry either. The helium present when the Earth was forming has drifted away into space. As Lockyer and Janssen observed, it is also a major component of the atmosphere of the Sun.
When Ramsay discovered the noble gases, some members of the family very quickly found uses. One of the first experiments the chemist performed on newly isolated neon at his University College London labs was to excite it with an electrode. The gas gave off a stunning red glow that was soon lighting up the streets of Paris and Los Angeles in the form of advertising signs.
Helium took a little longer to find a use. The process was eventually hastened by the outbreak of the first world war. A decade or so before the outbreak of war, helium had been discovered to be naturally present in some deposits of natural gas, notably in Texas. When the US entered the war, the Bureau of Mines issued contracts for the construction of three helium extraction plants.
For decades the US produced far more helium that it used, which it corralled underground in depleted gas fields. In , to recover the sizable debt it had accumulated buying up and storing all this helium, the US government announced a grand sell off of the stored gas — to the great concern of scientists. It was just one nanometer—a billionth of a meter. But the difference bothered Janssen.
Even after the eclipse passed, it kept picking at his mind. Had his instrument just been off-kilter? Janssen had also been surprised at how blazingly bright the anomalous yellow line was. In fact, it was so bright that he wondered whether he could detect it even outside of an eclipse. Unfortunately, clouds swept over India after the eclipse ended and covered the sun.
So Janssen spent the day reconfiguring his equipment to block out all other wavelengths except for those right around nm. The next morning, around a. Sure enough, he saw a blaze of yellow around nm. Janssen spent the next month refining his observations, then mailed a paper off to the French Academy of Sciences in Paris. It took his letter two months to reach Paris. And during that time, another scientist nearly scooped him.
The English astronomer Norman Lockyer spotted that same yellow line independently in October And unlike Janssen, Lockyer never shied away from leaping to big conclusions. So as soon as Lockyer saw that bright yellow line, he declared he had discovered a new, extraterrestrial element.
He named it helium—after Helios , a Greek god and the personification of the sun. Lockyer then staked his claim to helium by dashing off a paper to the leading scientific body in the world—the French Academy of Sciences.
Accounts differ on what happened next. If so, it must have been a chaotic scene—which scientist deserved credit? As it was, the French Academy decided that the two astronomers would share credit for helium. Still, other astronomers began to raise objections. Helium, they declared, was bogus. This, then, was the backdrop for the December 22, , eclipse in Algeria. Janssen needed to shore up his claim for helium, as it was still easier to observe that bold yellow line during an eclipse.
Plus, who knew what new surprises he might see this time around? In the summer of , the wily German chancellor goaded France into invading Germany and proceeded to rout the French army.
Bismarck then marched on Paris, surrounding it in just five weeks. Some historians call it the original blitzkrieg. Within weeks, people in Paris were chopping down trees on beloved boulevards for firewood. They took to eating pets, then animals in the zoo. With no way to escape the city and no other way to rally support, the desperate French government began sending people up in hot-air balloons. Most carried a few passengers, some sacks of mail, and a cage of passenger pigeons for return messages.
Ever stylish, the French gave the balloons dashing names—one was Liberty , another was Deliverance. They also honored several scientists, including Archimedes, Kepler, Newton, and Lavoisier. Unlike normal balloon flights, these commando runs leapt as high as possible as quickly as possible to escape the dreaded German artillery. It consists of a nucleus of two protons and neutrons, and two electrons in atomic orbits. The most common form is Helium-4, which is believed to be the product of Big Bang nucleosynthesis.
This event, which lasted from 10 seconds to 20 minutes after the Big Bang, was characterized by the production of nuclei other than the lightest isotope of hydrogen i. This event is believed to have produced the majority of helium-4, along with small amounts of the hydrogen, helium and lithium isotopes. All other heavier elements were created much later, as a result of stellar nucleosynthesis.
Large amounts of new helium are being created all the time through this same process, where the heat and pressure at the core of stars are causing hydrogen atoms to fuse.
The nucleus of the helium-4 atom is identical with an alpha particle, two bound protons and neutrons that are produced in the process of alpha decay where an element decays, releasing mass and becoming something else. This stability also accounts for the lack of interaction of helium atoms with each other, which leads to one of he lowest melting and boiling points of all the elements.
For some time, helium was believed to exist only in the Sun. However, in , Italian physicist Luigi Palmieri detected helium on Earth when analyzing lava from Mount Vesuvius after it erupted in that year. And in , while searching for argon, Scottish chemist Sir William Ramsay managed to isolate helium by treating a sample of cleveite with mineral acids. After treating the element with sulfuric acid, he noticed the same D3 absorption line.
It was independently isolated from cleveite the same year by chemists Per Teodor Cleve and Abraham Langlet in Uppsala, Sweden, who were able to accurately determine its atomic weight. Over the course of the next few years, similar experiments yielded the same results. Several interesting properties of helium were discovered in the ensuing years. In , Ernest Rutherford and Thomas Royds demonstrated that an alpha particle is actually a helium nucleus.
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