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We are home schooling my son, and right now we are covering chemistry- ionic bonds, covalent bonds, etc. We've talked about how carbon is "special" in that it can form very complex molecules (organic chemistry), and I have done some hand waving by saying that it is its ability to make four bonds that causes that specialness.

He, quite reasonably, asked why nitrogen, with its ability to make three covalent bonds, couldn't be almost as special as carbon. I told him that it probably can make pretty complicated molecules, but that only being able to make three bonds is a limiting factor. That didn't seem to satisfy him, and to be honest, it doesn't totally satisfy me.

So why is carbon so special? Is it just the four bonds vs. three, or is it something else?

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    $\begingroup$ Catenation (this is mainly what allows those complicated molecules) $\endgroup$ Commented Apr 26, 2016 at 0:55
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    $\begingroup$ Maybe this earlier answer will help. $\endgroup$
    – ron
    Commented Apr 26, 2016 at 1:05

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I think that the link that Ron mentioned answered the question adequately, although let me add my own take. (What makes carbon special and versatile?)

I heard that the reason carbon is able to make such stable multiple bonds is that its orbitals are close enough to its nucleus that they form extremely effective overlap when bonding. It is therefore the best atom because it is the smallest atom that can form four bonds. When you have 5 valence electrons already and can only make 3 bonds with 1 lone pair, that usually leads to weird bent shapes (although nitrogen is also pretty common in organic compounds).

It's kind of like, which hotel is more versatile in booking large families—a hotel with four open rooms right next to a breakfast bar (carbon), a hotel with three open rooms and a full room right next to a breakfast bar (nitrogen), or a hotel with any amount of open rooms, except you need to walk a mile for breakfast (any other element)?

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  • $\begingroup$ What is also important for carbon is that its bond to hydrogen is relatively strong and almost nonpolar. Therefore C-H bonds only react homolytically with high activation energies unless specifically activated in a molecule. The idea that C forms 4 reasonably strong bonds in a neutral molecule is a pretty close, good reason. $\endgroup$
    – jimchmst
    Commented Dec 5, 2021 at 0:54

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