When writers need to indicate that their super-advanced-spaceship crew are just as mystified by some alien artifact as you are, they often fall back on the tried and tested exclamation of "It's made of some unknown element!" This always caused my eyes to roll—after all the last gap in the periodic table of the elements was filled in 1923 and while scientists do compete to add more artificially created elements to the bottom of the periodic table, these elements are incredibly unstable, with half-lives typically measured in fractions of a second. And even if one of these new elements were stable, they'd all be much heavier than lead, whereas, when handled by the spaceship crew, the alien artifact tends to behave more as if was made of materials with, perhaps, the density of plywood or plastic. But now a group of Dutch researchers at the University of Delft have created substances that behave like totally a new type of element. By heating a silver filament up to just below its melting point, silver atoms begin to evaporate from its surface. These atoms begin to clump together in very specific ways—clumps containing 9, 13 or 55 silver atoms are preferentially formed. These atoms all begin to share electrons. To understand the significance of this you have to understand that most of the chemical, magnetic and electrical properties unique to an atom are based on the behaviour of the outermost electrons that orbit an atom's nucleus. When the silver atoms in a cluster start sharing electrons, to the outside world the whole cluster looks like one giant superatom with its own unique set of outer electrons—in effect, mimicking the behavior of a totally new, but stable and relatively lightweight, element. Scientists hope to one day make crystals from these types of superatoms, so who knows, we may be making our own mysterious artifacts in a few years.
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