An atom's electrons are an ever-shifting quantum melee, but it turns out you can still take their photograph as if they were standing still. A quantum-style microscope has imaged the hydrogen atom's wave function, the equation that determines its electrons' positions – and in turn the atom's properties.
The electrons that dance around an atomic nucleus help determine how the atom bonds with others, but they are notoriously difficult to pin down. Thanks to quantum theory, which says that tiny particles are in multiple places simultaneously, you can never say where a given electron actually is. The best you can do is say how likely it is to be in a given spot.
Not all positions are equally available: electrons can only reside at certain distances from the nucleus, with these distances related to how much energy the electron holds. In principle, the wave function, denoted by Greek letter psi, can be used to reveal these energy levels for any given atom or molecule, although in practice this has only been done for the very simplest – the hydrogen atom and molecule (made of two hydrogen atoms bonded together).
But how on earth do you make an image of such an object? Measuring the position of a single electron "collapses" the wave function, forcing it to pick a particular position, but that alone is not representative of its normal, quantum presence in the atom. "Wave functions are difficult to measure. They're exquisite quantum objects that change their appearance upon observation," says Aneta Stodolna of the FOM Institute AMOLF in Amsterdam, the Netherlands.
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