An Atomic Orbital

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An Atomic Orbital

When the a planet moves around the sun, you can plot a definite path

for it which is called an orbit. A simple view of the atom looks

similar and you may have pictured the electrons as orbiting around the

nucleus. The truth is different, and electrons in fact inhabit regions

of space known as orbitals.

Orbits and orbitals sound similar, but they have quite different

meanings. It is essential that you understand the difference between

them.

The impossibility of drawing orbits for electrons

To plot a path for something you need to know exactly where the object

is and be able to work out exactly where it's going to be an instant

later. You can't do this for electrons.

The Heisenberg Uncertainty Principle (not required at A'level) says -

loosely - that you can't know with certainty both where an electron is

and where it's going next. That makes it impossible to plot an orbit

for an electron around a nucleus. Is this a big problem? No. If

something is impossible, you have to accept it and find a way around

it.

Hydrogen's electron - the 1s orbital

[IMAGE]Suppose you had a single hydrogen atom and at a particular

instant plotted the position of the one electron. Soon afterwards, you

do the same thing, and find that it is in a new position. You have no

idea how it got from the first place to the second.

You keep on doing this over and over again, and gradually build up a

sort of 3D map of the places that the electron is likely to be found.

In the hydrogen case, the electron can be found anywhere within a

spherical space surrounding the nucleus. The diagram shows a

cross-section through this spherical space.

95% of the time (or any other percentage you choose), the electron

will be found within a fairly easily defined region of space quite

close to the nucleus. Such a region of space is called an orbital. You

can think of an orbital as being the region of space in which the

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