Question

What is the difference between an orbit and an electron orbital?

Answer 1

A better way to put the question is: is there any similarity? And the answer is pretty much no, they are completely different things, and the fact that the names sound similar is largely historical accident. About the only thing they have in common is that they describe stable states of electrons orbiting nuclei.

An orbit is an object from classical mechanics. It is the trajectory r(t) -- where r is position and t is time -- of a moving object in a bound state, typically because it's attracted to one or more other objects (although it's possible to have an orbit because an object is confined by repulsion from several objects, too). For example, the orbit of the Earth around the Sun is the trajectory of the Earth as it revolves around the Sun. More or less, a giant ellipse with the Sun at one foci. For a two-body system, all the possible orbits are conic sections -- a circle, an ellipse, a parabola or hyperbola. A single planet of a sun executes an ellipse (or possible a circle, in extremely rare circumstances). A comet that comes from and eventually recedes to interstellar space may execute a parabola or hyperbola. If you apply classical mechanics to a single electron orbiting a nucleus, then the electron should similarly execute a conic section orbit around the nucleus. In fact, it does not, for two reasons: first, because the electron obeys quantum mechanics, not classical mechanics, and second because an electron under acceleration radiates energy, and so a *classical* electron near a nucleus would actually spiral into the nucleus.

An orbital, by contrast, is a probability amplitude distribution produced by quantum mechanics, which gives (among other things) the probability of observing an electron known to be in a given stationary state at a given location. It is not at all like an orbit, because it makes no attempt to describe the trajectory of the electron -- that is, it does not attempt to say WHEN an electron is at a given point, only the probability of observing it at that point. A key mathematical distinction is that an orbit is a function of time, but an orbital is not.

It turns out that quantum mechanics forbids anything but the crudest possible orbits. It is not possible to describe the path taken by an electron in an atom with any useful degree of precision. (This is a result of the uncertainty principle.) If you want to know that the electron is confined to the atom (it won't wander off), then about all you can do is estimate the probability that it's at this or that position -- which is what an orbital does.

You may notice, by the way, that I restricted the meaning of an orbit to a two-body system, e.g. a sun and one planet. That's because even in classical mechanics, once you get more than two bodies, it is generally no longer possible to draw a precise orbit. You have what's called a "chaotic" system, and over long enough periods of time, the actual path of the moving body will deviate substantially from any orbit you can draw. That time may be quite long, of course. The orbits of the planets in the Solar System can be predicted with great precision out for at least millions of years.

Answer 2

thanks

Answer 3

Holy crap at least give the guy a medal!