NewScientist (15 April 2017, paywall) interviews Russian physicist Yuri Oganessian, who recently received the honor of having element 118 named after him. I found this Q&A interesting:
How much higher will the periodic table go?
There has to be a limit, and I think it will come from relativistic effects. When the positive charge of the nucleus increases, the velocity of the electrons increases too, bringing them closer to the speed of light. We are already close. For example, the innermost electrons of element 112 travel at seven-tenths of light speed. Bringing the velocity of the outermost electrons even closer to light speed may change an atom’s chemical properties, breaking periodicity.
That’s an interesting thought. But he also mentions another topic that fascinates me, if only because I’m so ignorant:
What are you looking forward to now?
To see closer to the top of the “island of stability“. Theorists predict that there should be some superheavy atoms, with certain combinations of protons and neutrons, that are extremely stable. We have a “continent” of stable elements that ends with lead, element 82. As we go heavier than lead, we have a “peninsula” created by the likes of thorium and uranium, which are radioactive and so decay over time into lighter elements. Superheavy nuclei are highly charged matter. The repulsion of positively charged protons prevents the formation of large nuclei and this moves us into the deep water of the “sea of instability”, where elements break down ever faster. It looks like the end of the material world, but I don’t think it is.
The island of stability is a controversial idea. You think it could exist?
If it didn’t, we could not synthesise elements heavier than element 112. Their lifetimes are extremely small, but if neutrons are added to the nuclei of these atoms, their lifetime grows. Adding eight neutrons to the heaviest known isotopes of elements 110, 111, 112 and even 113 increases their lifetime by around 100,000 times. This is because we are heading inland on the island of stability and I feel we are now on firm ground, but we are still far from the top of the island where atoms may have lifetimes of perhaps millions of years. We will need new machines to reach it.
Since I have no concept as to why some elements are radioactive and thus decay relatively rapidly over time, this doesn’t entirely make sense to me.
