True story. I was in the first or second grade. I guess I can tell you, it was around the mid-1970’s. And our science text book was talking about molecules and atoms.
We don’t know what shape molecules are, they told us. And to illustrate the point, they showed some molecules being poured from a glass as being square-shaped.
I don’t know, but I am guessing molecules–atoms specifically–are not square. They consist of a nucleus of protons and neutrons, with electrons circling around. And in art and science, they are usually depicted as spherical.
But that could just be one artist’s conception of what they look like up-close (forgetting also, for the moment, there is no way to see them up-close, for the moment, at least).
So I’ll cut to my point: What shape are atoms? I of course am talking about their constituent elements, protons, neutrons and electrons. Are they round? Do they have any shape, in the conventional sense? Or are they so weird, normal descriptions wouldn’t apply?
I doubt that they have a shape in the conventional sense. They mostly consist of empty space, populated by particles which are related to one another by forces. The forces have no form and the particles are pretty amorphous too. And, if we believe Heisenberg, the position of the particles is not always knowable.
Somebody who actually knows something about atomic physics will be along shortly.
You do of course need to define what you mean by “shape”. Given atoms and molecules are indeed built from constituent things, a definition of shape needs to allow for the nature of the constituents. For instance, if I asked you what shape a crowd of people were, you would probably not get too worried about the nuances of who was walking where at any instant.
Mostly the useful idea of the shape of atoms or molecules is the shape of the electron cloud, and to be more specific, the electron density. This already gets you a bit of a problem with a definition of shape, as it isn’t a surface. Rather it is a distribution in 3D space of density values. You can define a surface over this, by picking a density, which gets you an iso-surface, and thus a 3D solid shape, but you can choose any arbitrary value for your density, and get different shapes.
But for some chemists, and particularly bio-chemists, that electron density distribution is absolutely what they want to know about. It controls a very large fraction of how big molecules interact and how a big slab of complex biochemistry works.
For other chemists it is all about the manner in which the electrons in the outer orbitals interact with one another via QED (Quantum electro-dynamics.) QED controls the electron density, so the two are interrelated. For small enough molecules you can look at the QED effects in detail to predict how the chemistry works.
An important point is that molecules are not made in a fixed geometry. The bonds holding the atoms together allow some wiggle room, and the atoms bounce around as if on the ends of springs. This wiggling is also of considerable importance in much chemistry. So here the overall geometrical shape matters. Chemists will talk earnestly about bond angles.
Even a single naked atom does not have a simple spherical electron density. Again the weird nature of QED comes to play, and the rules of how electrons can assemble around a nucleus cause different pinched distributions to occur.
This is true, but the electron cloud exists in three dimensions and ISTM that it can be said to have the same probabilistic distribution in any given radial direction from the nucleus – i.e.- a sphere, more or less, or a roughly spherically shaped “sphere of influence”. The pictures in this article seem to be pretty vivid evidence of the fact that atomic bonds extend fairly uniformly in 3D space and form close but imperfect variations of the theoretical bonding patterns.
There are some molecules for which we don’t know their exact shape because they’re very complicated. Many proteins fall into this category, for instance, and understanding just what shapes protein molecules form is fairly significant in biochemistry. Nowadays, we can (with great difficulty) figure them out using computers, but that probably wasn’t possible when you were in grade school, and there are still a great many for which we haven’t yet figured out the shape.
But the simple molecules like water, methane, or nitric acid? Yeah, we’ve got those shapes down pat.
Francis Vaughan gave a good answer about the electron cloud which is a probability distribution, not a shell or satellite-like circular orbit. Atoms have a defined size called the atomic radius: https://en.wikipedia.org/wiki/Atomic_radius
Re shape of the subatomic particles themselves, electrons are considered point particles with no internal structure and no physical size, therefore they have no defined shape.
Protons and neutrons are often considered spherical but since we know they are actually constructed of quarks some physicists consider them ultimately non-spherical:
Re your school experience, this is often sadly the case in physics education, even at the secondary levels. This funny yet educational video illustrates the problem: https://www.youtube.com/watch?v=BGL22PTIOAM
I think saying that atoms are spheres and molecules are spheres stuck together is good enough for 8-year-olds … only Tiffany would carry around quantum physics books late at night in the ghetto …
What shape is an evacuated glass tube? The empty space part has nothing to with the shape. Saying that atoms are populated by “particles” just pushes the shape question further back, and in the context of a “shape” discussion, we probably shouldn’t use terms like “particles”. At the quantum level, the best we can say is that these “things” are a fuzzy, cloud-like probabilistic distribution function with no defined border. The simpler the atom, the more spherical the distribution function will seem at any given time.
All the forces that pull the atomic “particles” together or push them apart are spherically symmetrical. Perturbation may make the cloud look non-spherical at times, but it’s generally going to want to tend to be spherical on average.
Novice and primary school materials often depict atoms as if they were marbles, or perhaps miniature solar systems where smaller marbles (electrons) orbit a central cluster (the nucleus) on predictable paths. My chemistry teacher called this a “useful lie.” Sometimes you have to resort to a simplified model until the student is ready to grasp the more complex reality.
I imagine an atom looking something like a sparkler firework… Just this indistinct ball of glittering light that constantly shifts and moves. The comparison to a crowd of people is apt. When examining the shape of an atom we do not know, and we really can’t ever know exactly what it looks like. When we try to define where electrons are in relation to the nucleus, all we are really saying is we have certain zones where we expect electrons are most likely to be found.
At least in the U.S. it is not just grade school children that are taught this. It continues through high school, including 2nd year Chemistry and Physics.
There is a common view that teaching even a simplified version of quantum physics to high school students is too hard and that those who go to university will eventually learn the truth and aren’t really handicapped by being taught the wrong thing for several years. This view is typified by the paper “Why we should teach the Bohr model and how to teach it effectively” (McKagan, et al): http://journals.aps.org/prper/abstract/10.1103/PhysRevSTPER.4.010103
However many educators call today’s common secondary school physics curriculum “A deformed vision of science”, Gil, D. P. & Solbes, J., 1993.
At the high school level, it’s not necessary to teach quantum physics or the Schrodinger model with a high degree of mathematical formalism. There are various possible ways this could be taught. Numerous papers have addressed this: Arons, 1990; Aubrecht, 1989; Cuppari, Rinaudo, Robutti, and Violino, 1997; Fischler & Lichtfeldt, 1992; Gil & Solbes, 1993; Jones, 1991, 1992; Lawrence, 1996; Müller & Wiesner, 2002; Petri & Niedderer, 1998; Stannard, 1990.
You are right that teaching outdated, erroneous information to high school students IS a “useful lie”. It’s useful to the teachers. It is easier than teaching truthful updated information. Unfortunately it’s not useful to the students.
Expanding on Francis Vaughan’s post a bit, in case you aren’t familiar with isosurfaces.
Suppose you look at a map and ask what shape a mountain is. This isn’t a well-defined question, because a mountain is a 3D object while a map is 2D.
What you can do, though, is look at the shape for a given altitude. You might draw the outline of the mountain at exactly 1000 feet.
This doesn’t give you all the information you need about the mountain, it might be enough–especially if you expect the shape to change smoothly with altitude. A circular cross-section is at least a hint that the mountain is conical. Topographic maps do this, but with several different altitudes at the same time.
You can do exactly the same thing with atoms, except with 4D mapped down to 3D. The fourth dimension isn’t time here, but the “electric potential” (or electron density, or some similar measure). The exact nature of this potential isn’t too important, just that it gives you a number for every point in space, just as a mountain has a number (altitude) for every point on its surface.
So you can pick a reasonable value for the potential and come up with a shape that consists of all points where the potential matches your value. You’ll get a shape that tells you something about the nature of the atom, even if it’s only a slice of the big picture.
The shape is called an isosurface, iso- meaning “equal”–that is, it’s the surface where all points have equal values for some parameter.
IBM has a microscope that works by measuring the force on a really tiny needle (called atomic force microscopy). They move the needle around a surface, and when there’s an atom, it pushes back on the tip (due to their electron clouds overlapping). They can measure this force and from it, get a map of the height of the surface. They can move the needle around with sub-atom precision and thus see the shape of atoms and molecules (at least from the top).
Past that, the visualization is computer generated. All they get from the microscope is a height map. They chose to render it as metallic, so the atoms look like ball bearings. Atoms don’t actually reflect light like that.
