Why does carbon form multiple bonds with oxygen while silicon does not?

Expert Answers
enotechris eNotes educator| Certified Educator

Actually, Silicon does!  Carbon can form various molecules with oxygen, depending upon the number of bonds.  For a single bond, carbon monoxide (CO) is formed; for a double bond, carbon dioxide (CO2) is formed, and even carbon trioxide (CO3) can form with a triple bond, although it is unstable.  Similarly, Silicon can form the same analogues as carbon -- Silicon oxide (one bond -- SiO) silicon dioxide (two bonds -- SiO2) and silicon trioxide (three bonds -- SiO3.)

It's not surprising Silicon can form similar compounds to Carbon, as it is in the same family in the Periodic Table, Silicon being right below Carbon.  However, carbon compounds are more stable, since the carbon bonding allows for the atoms of carbon and oxygen to be closer and held more firmly that those of silicon.  Because it is a bigger atom and there are more shielding effects by the electrons, the bonds between atoms with silicon are not as strong.

sossya | Student

The article listed below provides some theoretical insight into the stability of silicon oxygen double bond that explains its extreme reactivity, especially with polar molecules.


Dr. Dishakjian

sossya | Student

Please open the following pdf for more about Silicon Oxygen bond


Dr. Dishakjian

sossya | Student

First, I would like to note that carbon and oxygen in CO are held together by triple bonds; one sigma and two pi bonds; not a double bond and in CO3, an unstable compound, the bond is not a double bond.

As to the Silicon compounds, SiO is very unstable gaseous compound, and in SiO2, the structure is like diamond and not like CO2. The SiO bonds are tetrahedrally bonded to 4 oxygen atoms.

Although Si is in the same group as carbon; that is Group IV, the valence orbitals of silicon are much larger than that of carbon and oxygen, and are at higher energies.

For stable pi bonds to form between two atoms, the participating valence orbitals of the two atoms should have similar sizes and similar energies, such as between carbon and oxygen; two elements in the same period. This is not case for silicon and oxygen, as a results, even if pi bonds form, the compounds tend to be very unstable.


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