Most Detailed Photos of an Atom Yet

BuzzSkyline writes "Ukrainian researchers have managed to take pictures of atoms that reveal structure of the electron clouds surrounding carbon nuclei in unprecedented detail. Although the images offer no surprises (they look much like the sketches of electron orbitals included in high school science texts), this is the first time that anyone has directly imaged atoms at this level, rather than inferring the structure of the orbitals from indirect measurements such as electron or X-ray interferometry."

Comments

Speaking as a chemist

[PatrickThomson]

This is amazing. We'd theorised orbitals to exist, and they worked very well. We could calculate the shapes of molecules and make detailed predictions that came true to 10 decimal places. Quantum mechanics as applied to electrons in atoms is the most successful and the most rigorously tested theory ever developed.

And yet, to finally see a real orbital, not a simulation. Looks like a 1s and a 2p, right there for the looking!

Re:Speaking as a chemist

[PatrickThomson]

Basically, a chemistry education is very much like fast-forwarding through 300+ years of science history. Some dead-ends are skipped, but by and large, the simpler and more self-contained a theory was, the older it is and the earlier it's taught in school. The university-taught molecular orbital theory is (debatably) too rich and complex to be taught any earlier.

The moons-orbiting theory fit with all the available evidence at the time it was developed. Think of orbitals as clouds of probability where, if you tried to pin down the electron, it might be. A moons-orbiting theory would give this probability cloud as a thin donut around the atomic waist. The shapes of orbitals as depicted in wikipedia etc. are consequences of the maths of quantum mechanics. It's annoyingly non-intuitive.

Re:Speaking as a chemist

[PvtVoid]

Speaking as a chemist, could you explain what exactly this means? Up until this very moment I have been under the misguided notion that the nucleus of an atom was orbited by electrons within groups called "shells", and these worked very similarly to satellites around a planet.

You're thinking of the Bohr model.

So, could you in any way explain how we get from "think of it as a planet with many moons" to this or more importantly, what gives orbitals this shape?

It's because the Schrodinger equation is a Laplacian, and the hydrogen atom is a spherically symmetric problem. The natural basis for the Laplacian in spherical coordinates is spherical harmonics. The shape you are seeing is the characteristic shape of different spherical harmonics, corresponding to the angular momentum of the electron.

Re:Speaking as a chemist

[The_Duck271]

At atomic scales electrons cannot be thought of as points; instead they are smeared out probability distributions. They don't exist at any given point, there's a chance for a given electron to be found throughout a whole region of space, and the probability of finding it at any given point is given by a probability distribution. These probability distributions are called wave functions, and given an electron's wave function you can calculate the likelihood of getting different results when you take a measurement of the electron. It is a strange aspect of quantum mechanics that you can't calculate exactly what you will measure, you can only establish the probabilities of each possible outcome.

Another aspect of quantum mechanics is that if you measure, say, the energy of an electron in an atom, you can only get one of a certain set of discrete values, and never any energy in between those values. The energy of the electron is quantized. In general, if you measure an electron's energy you have a certain probability to get a result corresponding to the first energy level, a probability to find it in the second energy level, and so on. This is also the case for some other things you can measure, like angular momentum.

However, there are certain wave functions that correspond to exactly one value of energy; that is, if you have an electron with this wave function, you are guaranteed to get a certain energy value when you measure it. In fact, there is a special set of wave functions with the following three properties:

• They each have a definite energy level.
• They each have a definite total angular momentum around the nucleus.
• They each have a definite angular momentum around the z axis.

These wave functions are the atomic orbitals that are so important in chemistry. If you calculate the shapes of the wave functions that satisfy these properties, you get the shapes shown on the Wikipedia page. They are listed in a table indexed by the variables n, l, and m. n corresponds to the energy level, l corresponds to the total angular momentum, and m corresponds to the angular momentum around the z axis. For example, you can see that orbitals with high m (angular momentum around the z axis), like the ones on the very right of the Wikipedia table, are sort of flattened out by the centrifugal force from spinning fast around a vertical axis.

Unscaled photo link

[UPi]

The unscaled photo is here:

http://insidescience.org/polopoly_fs/1.918!image/671260397.jpg

Re:Unscaled photo link

[PGC]

Unscaled, wow. That is one HUGE atom.... no wonder they were capable of photographing it.

Re:really?

[ModernGeek]

The shadows are all wrong.

Re:(do not mod)

[machine321]

MOD PARENT UP!

Not quite a of an electron in an orbital

[Richard Kirk]

They do look like the classical orbitals, don't they?

However, there are some problems with interpreting the image as a photograph of an orbital. What the FEEM does is to charge up a very sharp point. The actual voltage may not be very big, but the local field strength depends on screening and curvature, so you can get very large electrostatic fields around sharp features, and if you get the balance right, electrons will leave the sharp points, zoom down the field lines, and get imaged. I remember seeing a sharp tungsten needle in a FEEM back in the seventies, and seeing the individual atoms. This sort of thing provided the first real evidence of a screw dislocation. You got a strange projection of the tip of the needle, as the electrostatic field tended to map the roughly spherical tip onto a flat plane.

So what is happening here? Our field stripping an electron from the orbital. We are getting a map of the electron flows as focused by the electrostatic field. We calculate the trajectory back through the electrostatic field and guess some sort of map of emission. They must have stripped hundreds or thousands of orbital electrons from the same atom, and replaced them to get each image. However, if an orbital 'pokes out' of the atom, or forms a 'sharp feature' (inverted commas because they are wave functions, so these concepts are a bit hard to define) then we get a bright spot. The really cool bit is getting the atom to go back to the same hybridization state hundreds of times, so we got the two-lobed picture.

It's dead clever. However, for my money, the atomic force probes are cooler as they can measure the fields without stripping the electrons. But, as the reviewer said, it takes all sorts...

Re:really?

[nacturation]

Looks like a smurf sat on the photocopier.

Re:It makes me very suspicious indeed.

[Anonymous Coward]

The article was extremely superficial when describing the actual experiment, but essentially a current was passed through a small chain of carbon atoms by applying a voltage across the chain. The current caused the the carbon atom at the tip to give off electrons to a phosphor screen. I would suppose that these "given off" electrons were integrated (summed) over time and this formed a pattern that reflected the shape of the probability distribution, i.e. orbital. Each electron that was "given off" constituted a sampling experiment regarding electron position, and the sum total of the samples would, over time, give rise to the orbital shape. In the case of an s orbital, electrons were given off in all radial directions. For the p orbital, certain angles gave off no electrons. This behavior corresponds to the quantum equations.

Pity this is AC

[Kupfernigk]

Thanks for responding. This could do with some mod points but I can't mod and post...so I'll respond. It's interesting to think about what is happening here. It's possibly unhelpful to refer in the same sentence to "current" and "electrons" but I know what you mean, though I would rephrase it a little to help my own understanding. The "current" did not cause the carbon atom to give off electrons; rather, the potential difference enabled some electrons to pass along the carbon chain until they left the tip, and the path of the emerging electrons was probabilitistically interfered with in a way that reflected the solution of the Schroedinger wave equation for the outer electrons of the end atom. That's a very interesting experiment. The benefit of using carbon atoms in a molecule is that the bond angle presumably locks the orientation of the P orbitals sufficiently to enable the experiment. So for many atoms it simply wouldn't work, and what we are seeing here is not an image per se but something more like the result of the Rutherford/Geiger/Marsden experiment. It looks like a significant experiment, but the summary is quite wrong as to what is being shown.