0
$\begingroup$

What exactly is the definition of "giant covalent molecule"? All sources online don't give a definition but instead, allude to properties of examples of giant covalent molecules (such as diamond and graphite). What does the "giant" mean?

To this end, is table sugar (sucrose, $\ce{C12H22O11}$) a giant covalent molecule? I reckon that since it is a covalent compound with a crystalline structure, it should be a giant covalent molecule. Is my reasoning correct?

$\endgroup$
8
  • 1
    $\begingroup$ No. It is a small molecule. Ten times that big is still small. Pretty much all compounds have crystalline structure. This is irrelevant. $\endgroup$ Oct 19 at 8:08
  • 3
    $\begingroup$ Some expressions do not have explicit and unique definition, like a "giant person". Stay with meanings of "giant", "covalent" and "molecule". BTW, it is not fructose, but sucrose. Is sucrose molecule at least as big as molecules of polysacharides, proteins and DNA to be a giant candidate ? $\endgroup$
    – Poutnik
    Oct 19 at 8:08
  • $\begingroup$ @Poutnik My apologies, I meant sucrose; edited that part of the question. So the whole idea of "giant covalent molecule" is pretty much arbitrary? $\endgroup$
    – Tham
    Oct 19 at 8:20
  • $\begingroup$ @IvanNeretin I was under the (probably erroneous) assumption that since table salt is a crystalline lattice structure and is considered giant, table sugar would also fall into this camp since it is a crystal. Does it mean that being a crystalline lattice structure is not a sufficient condition in determining the size of the compound? $\endgroup$
    – Tham
    Oct 19 at 8:25
  • $\begingroup$ @Poutnik Oh ok, I get it now. Thank you for explaining! I'm quite new to chemistry so pardon my confusion over simple questions like this. $\endgroup$
    – Tham
    Oct 19 at 8:32
5
$\begingroup$

The giant covalent molecule (GCM) in your context is a molecule ( 3D for diamonds, 2D for graphite ), which size is more or less (breaks are possible) limited just by the size of the particular solid phase region.

If sucrose molecules were interconnected by covalent bonds forming in the ideal case a single molecular structure of the size of the whole crystal, than it would be a GCM. But they are not. Sucrose crystals are formed by independent molecules. ( Table salt is a ionic compound, it does not form covalent molecules.)

Wikipedia.org - Covalent_bond -Covalent_structures says:

There are several types of structures for covalent substances, including individual molecules, molecular structures, macromolecular structures and giant covalent structures.
.......
Network covalent structures (or giant covalent structures) contain large numbers of atoms linked in sheets (such as graphite), or 3-dimensional structures (such as diamond and quartz). These substances have high melting and boiling points, are frequently brittle, and tend to have high electrical resistivity. Elements that have high electronegativity, and the ability to form three or four electron pair bonds, often form such large macromolecular structures.

$\endgroup$
2
  • $\begingroup$ I know table salt is an ionic compound; I was just thinking of "since table salt has a crystalline lattice structure and is considered to be giant, maybe 'crystalline lattice structure' is a sufficient condition for being a 'giant'" and extrapolated 'giant' to covalent molecules. I know now that it doesn't simply work that way. Thanks for taking the time to clarify. $\endgroup$
    – Tham
    Oct 19 at 8:51
  • $\begingroup$ @Tham Here, «crystalline lattice structure» merely refers to the regular spatial arrangement of the molecules: ideally, 1) it is possible to define a tiny parallelepiped (the unit cell) about the shape of the molecules, their orientation and distance to their closets neighbors. Then 2) any other location may be described by this unit cell, because the crystal is built from identical unit cells placed next to/on top of this reference unit cell by translation (similar to stacking shoe boxes), regardless if molecule(s) in this box is/are big, or small. $\endgroup$
    – Buttonwood
    Oct 19 at 11:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.