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View Diary: Overnight News Digest 10/18/2013 (42 comments)

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  •  orbitals (1+ / 0-)
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    What is shape of an s orbital?

    In: Chemistry, Planetary Science


    The probability density cloud for the orbitals are:

    s-orbitals are shaped like spheres.

    The three p-orbitals have the form of dumbbells.

    The three p-orbitals ina shell each are oriented at right angles to each other

    Four of the five d-orbitals are four pear-shaped balls.

    The fifth is a torus.

    Thee seven f-orbitals can best be described as "complex"

    atomic orbital

    Value of l    Corresponding Subshell Label
    0    s (sharp)
    1    p (principal)
    2    d (diffuse)
    3    f (fundamental)
    4    g



    First off, in order to have a "look," things have to reflect light. Since atoms are far tinier than light waves, we can't see them with light.

    After physicists discovered that atoms were made of a positive nucleus surrounded by negative electrical charge, they began wondering why the charges remained apart. An obvious analogy was planets orbiting the Sun.

    One problem with this idea was that if you force electrons to travel curving paths, they emit radiation. Electrons should emit radiation, lose energy, and spiral into the nucleus.

    Physicists were forced to postulate that  for some reason, electrons around atoms simply didn't do this. Also, since the electrons had definite energy levels, they postulated that one of the rules of atoms was that electrons could only have specific energies, and nothing in between those energy levels.

    Using these rules, the Danish physicist Niels Bohr came up with a model of atoms much like a solar system. Although textbooks usually show Bohr's atom as having circular orbits, physicists actually explained some of the subtleties of electrons in terms of elliptical orbits.

    Bohr was able to explain the energy levels of hydrogen atoms in great detail. Other atoms (like sodium) where there is a single outer electron well removed from the inner electrons, also behave much like hydrogen. However, nobody was ever able to describe atoms with multiple electrons in exact detail using a planetary interpretation.

    By the 1920's, physicists had discovered that matter also has wave-like properties and that it just doesn't work at the atomic level to regard particles as tiny points with precise locations and energies. Matter is inherently "fuzzy." They gave up thinking of electrons as tiny planets altogether.

    In a way, it's unfortunate that Bohr's hydrogen atom worked as well as it did. To this day, even advanced physics books use it as a way of introducing quantum mechanics. But it's just plain wrong.

    And the terminology that came with Bohr's atom, of "orbitals" and "spin," reinforces the image of electrons as tiny planets even though physicists have long since given up the literal imagery.

    At least the weird terminology that quark physicists use, of "color," "flavor," and "charm," carries no danger of being taken too literally. Nobody is likely to believe that quarks are really red, taste like chocolate, or flirt. So forget that you ever heard of the solar system model of atoms. Abandon all planetary concepts, ye who enter here.


    Electrons occupy discretely different energy levels, and since these differ in size as well, there's no harm in using the traditional term "shell" to describe them. They used to be lettered K, L, M and so on with increasing distance from the nucleus, and x-rays emitted by electrons in different shells are still denoted by those terms. In fact, it was the discovery that atoms emitted x-rays in sharply defined energy levels that led to the discovery of electron shells in the first place. For most purposes chemists and physicists just number the shells 1,2,3.. out from the nucleus. 1 = K, 2 = L, and so on.

    Within each shell, electrons occupy sub-levels, of which the most important are called orbitals. With increasing energy, they are called s, p, d and f orbitals (from sharp, principal, diffuse and fundamental, relating to the spectral lines produced by the alkali metals). These have size and shape, but attempting to portray them or describe them can lead to many misconceptions:

    We’re enablers. We’ve become enablers. We can’t be that anymore. ~ Minority Leader Nancy Pelosi, D-CA

    by anyname on Sat Oct 19, 2013 at 02:05:01 AM PDT

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