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Name: Rahul
Status: student
Grade: 9-12
Location: CA
Country: N/A
Date: September 2006

Question:
Hi.

Can you please tell me the difference between orbitals and orbits? I would like to know whether orbits actually exist, and how should I try and visualize orbitals in different energy levels?



Replies:
Rahul,

I often find that if I am confused to what the differences are between two things, that looking up the definitions of the words in question helps tremendously.

Taken from Dictionary.com, the definition of orbital is "a wave function describing the state of a single electron in an atom (atomic orbital) or in a molecule (molecular orbital)." and also "the wave function of an electron in an atom or molecule, indicating the electron's probable location." The definition of orbit is "Physics. (in Bohr theory) the path traced by an electron revolving around the nucleus of an atom.

To put things in simplest terms, an orbit is the path an electron takes around an atom and an orbital is a shape resulting in the combination of all probable orbits. In another example, let us take the Earth orbiting the Sun. Each year the Earth completely revolves once around the Sun. The specific path that you could draw out is the orbit. But each year, the Earth takes a slightly different path--whether it is slightly high or lower, or closer or further away than last year. You can physically compare the two different orbits that the Earth took. Now, let us say that you recorded the Earth's orbit every year for a million years and then you combined all of these orbits into one massive shape. You would result in something that looked pretty much like a big doughnut. This doughnut would be the orbital that Earth is confined to, much the same an electron's orbit is to the nucleus. I believe that the shape of an orbital is defined as where the electron is predicted to be 99.99% of the time (or some very high probability). So that resulting shape is the orbital.

Matt Voss


Rahul,

Strictly speaking "electron orbits" refer to the Bohr Model of the atom. This is a way of visualizing the fact that electrons in an atom have a particular energy and are limited to a small set of possible energies; the electron energies are quantized.

"Electron orbitals", on the other hand, refer to the Schrodinger Model of the atom. In this model, mathematical equations are used to describe the likelihood of an electron having a particular energy being in a particular location in an atom.

Since both of these concepts are models of the atom, strictly speaking, they are conceptualization, ways of imagining or describing an atom. Whether the electron truly exist in a circular orbit or in a mathematical orbital is irrelevant. What matters is that, given the strict parameters of the model, the model is able to predict certain chemical and physical properties of the atom.

Thus the orbit model of an electron is sufficient to predict the light emission and energy absorption of the hydrogen atom. The Schrodinger model, with its fuller description of electron energies and probable locations, is able to do more than that.

Please be very careful in the visualization of both models. The moment you visualize a model, you are translating the strict parameters of the model into a visual metaphor and this can lead to many misconceptions. While you do have to find a way to internalize the model, try to do this without adding to the model ideas that are not within the parameters of that model.

Greg (Roberto Gregorius)



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