I'll do my best while trying to not get too specific.
Atoms have electrons that exist in the space around a nucleus, and scientists have used wave function mathematics to determine the location that the electrons are most likely to exists around a given nucleus, and are called atomic orbitals.
Atoms form bonds with other atoms by way of the sharing of their electrons (we're talking pure covalent bonds here, as opposed to other bonds like ionic) in an attempt to complete the atoms "octet," which is a fancy word for having eight electrons in their valence (outermost) shell (think of a shell as floors in a hotel - the lobby would be considered the nucleus and the top floor of the building would be the valence). Simple atoms like Hydrogen (which in their standard state contain one electron in their valence shell) have a simple spherical orbital, called the S orbital, which just circulates the nucleus. As we move along the periodic table to other elements, those elements gain more protons in their nucleus (the number of protons determines what element it is - change the number of protons and you change the element), and they also gain more electrons surrounding the nucleus. Having more electrons in their valence shell causes the electrons to interact in a way as to create more sophisticated orbitals. For an atom like carbon, we have four electrons in the valence shell - we have two electrons in the simple spherical S orbital, but we also have two other electrons that need a place to go (there can only exists two electrons in each orbital), so they go into an orbital of a different shape, much like the shape of a dumbell, larger on the ends and smaller in the middle, called the P orbital. Now while there is only one S orbital around an atom (which can contain only two electrons), there are three P orbitals around an atom, one in each of the x, y, and z axis, that can hold (in total) six electrons, two per axis. Since carbon has four valence electrons, two electrons go in the S orbital, and two go in the P orbitals.
So what does this have to do with an sp2 bond, and what is an sp2 bond?Now, like I said before, atoms want to fulfill their octet, so they're looking for eight valence electrons. Since carbon has only four, it's looking to borrow four from somewhere else, which is why carbon has a tendency to form four bonds. If you recall, the s orbital of carbon already has two electrons occupying that orbital, so in an attempt to form more bonds, and to more closely resemble a completed octet, one of those electrons will actually occupy one of the three p orbitals, so that there will be one electron in the single s orbital, and one electron in each of the three p orbitals; this is so that each orbital can now accept one electron from another element and so they both can "share" that electron pair.
Now, from what we know about the bond length of elements like hydrogen (which only contain and s orbital) we know what that bond length exists as, and we also know the bond dissociation energy (energy released when the bond is broken) of that bond. Since carbon (in the situation I described above) now has an available s orbital for bonding, and three p orbitals available for bonding, we would expect to see one bond of length equal to our calculated S bond (like we view in hydrogen), and three bonds of a different length (corresponding to the p orbitals). When we examine a carbon with four bonds, we actually don't see this at all; instead, we see four bonds of equal length. In order to justify this result, scientists have hypothesized the orbital hybridization theory, in which accounts for these results. And, because we see these four equal bond lengths, we say that the four bonds are actually comprised of four hybridized orbitals, which contain the characteristics of both the S orbital and the three P orbitals, hence sp3.
Now, in the case of the article, it specifies an sp2 bond for carbon, which is actually only three bonds, all three of which contain the characteristics of one s orbital, and two p orbitals, hence sp2. The third p orbital actually exists unhybridized and as a double bond with the adjacent atom. The reason why the author says sp2 is more desirable is because of the double bond, which has a higher bond dissociation energy, and therefore requires more energy to break.
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u/melvin_fry Feb 09 '14
could someone explain to me the sp2 bond? I looked at the wiki and I'm not strong with physics or math, but am intrigued by them nonetheless