I watched a show recently which showed that we could actually see atoms and showed some images. It even showed a small movie where one atom was even moving and squeezing between 2 others. The atoms looked like little bubbles that were flexible…almost amoeba-like.
I have heard that the nucleus is very small so we can’t be seeing that, right? If so, what are we seeing? What are these ‘bubbles’?
Well what we’re actually doing is taking the measured distance between the tip of a atomic force microscope and a material and then colour coding it so you can “see” the resulting topology. The tip of the microscope and the material interact and those interactions translate to a separation. Since those interactions are electromagnetic, we’re looking at the electron shells… though that implies that they’re solid which isn’t the case.
So it’s a bit like brass rubbing, in terms of rendering a phenomenon as an image?
Here’s an analogy.
Take a brass plate, give it a change and hide it behind an opaque sheet of material. The sheet isn’t really there, I’m just using it to keep you from “seeing” the brass plate. Now measure the potential difference between the plate and your measuring device at position (x[sub]0[/sub], y[sub]0[/sub]). Now do that again and again and plot it out on a piece of graph paper. The measured values will differ based on the seperation between plate and device.
Now colour code each square with low values begin black, mid values begin grey and high values begin white. Given enough resolution you now have a picture of your brass plate without ever really seeing it.
Oh I should mention the brass plate in question would be like the ones Mangetout mentions - something like http://www.ottawabrass.on.ca/uploads/files/IMG-20130909-00347.jpg
There is a mismatch between (1) How you imagine an atom looks (2) How it is shown on an atomic force microscope, and (3) How it would really look if you could “see” it.
Some microscopes can show a general region of the electron cloud surrounding an atom. These may appear somewhat spherical due to limitations of the microscope and processing. They cannot show the nucleus which is 125,000 times smaller than the electron cloud surrounding it.
If the sun was an atomic nucleus, the electron cloud (as defined by the atomic radius) would be 30 times further away than Pluto.
In fact the electron probability cloud (or orbital) surrounding an atom is not spherical or shell like, but exists as shaded regions of probability having various shapes, depending on the energy state and type of atom. There is a smartphone app which shows this, but I haven’t used it. This is much closer to what an atom actually “looks like”:
Best teacher I ever had was in a High School chem class. (Hi, Papa Voltz! You still alive?)
He got me to think of those “clouds” as a mapping of the probability of where the electron(s) might be.
That started 40+ years of my thinking of science as having fuzzy edges, where even if we’re not sure of something, we often have some solid guesses of what it should be like.
I suspect a good approximation is to an isosurface of the electron density. Usefully this is a common way of visualising molecules, so there is some commonality with what is seen and other science.
As noted above - there is no actual individual surface, solid or otherwise. It is a matter of convention in setting the parameters of the microscope how much force is used to set the breakpoint where it images the surface. Turn the force up and the surface will shrink towards the atoms, turn it down and the surface will open out. However there is likely a useful range of values where the image is sensible. The force versus apparent diameter of the atoms is not going to be very linear.
I would imagine that if one was patient enough, and the subject was disturbed, you could run many passes over the subject with different force settings and thus map out the 3D volume of electron density - at least across a range of values. But it would be tedious, time consuming, and the subject may not cooperate long enough.
A quick Google turning up this tutorial on electron density maps - which should give a good idea. Tutorial: Electrostatic Potential Maps
Don’t electron microscopes produce the electric field density graph ? Which can be represented as the dots of where the higher density is ? Perhaps the nucleus forced to stay in one orientation by magnetic field…
Electron orbitals can be complex and layered. They are not like shells or 3-dimensional solids as often depicted. They are shaded probability volumes. Scroll to the bottom of this page to see examples:
From a quantum mechanical perspective electrons don’t actually orbit the nucleus, IOW they don’t have a continuous trajectory. Rather they are quantum particles of zero size that have a probability of being found in a given place, and that probability can be represented as a shaded 3D volume.
By orientation if you mean the pitch/roll/yaw orientation of a nucleus, this isn’t normally “forced” to stay in one place but it can be influenced by magnetic force – that’s now Nuclear Magnetic Resonance works.
If you mean the spatial position (not orientation) of the nucleus with respect to the electron orbital, from a classical model this is not really maintained by anything. Electrostatic force attracts the electron toward the nucleus. The Pauli Exclusion Principle says they cannot be localized there, so the electrons “stack” in so-called shells or (more accurately) orbitals. As you can see from the above atomic orbital graphics, at the quantum level, particles do not behave like billiard balls or baseballs or anything else you have ever experienced. Their behavior cannot be evaluated from via familiar physical intuition. However the nucleus is thousands of times more massive than the electrons. From this standpoint you could visualize the nucleus as holding the electron orbitals in place, rather than the electrons holding the nucleus in place.
Rib Lake? Bemidji?
Nice ambiguity/play on “sense” there. Interesting.
