Question

Which gas, acetylene (`C_2H_2`), a gas used in welding, or ethane (`C_2H_6`) has a stronger carbon to carbon bond energy and bond length? Explain why.

Answer 1

The triply bonded acetylene molecule............

Explanation:

The modern chemical bond is conceived to be a region of high electron density between 2 positively charged atomic nuclei, such that internuclear is repulsion is negated, and a net attractive force results. The idea can be extended to multiple bonding, where electron density is concentrated in planes NORMAL to the `"atom-atom vector"`, but which still allows nuclear/electronic interaction.

So let's look at the bond dissociation energies. As chemists, as physical scientists, we must examine the data:

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And representative values for `C-C` bond lengths for `H_3C-CH_3`, `H_2C=CH_2`, and `H_3C-=CH_3` are `1.54xx10^-10*m`, `1.34xx10^-10*m`, and `1.21xx10^-10*m`.

And `C-C` bond energies:

`C-C:`, `84*kcal*mol^-1`;

`C=C`, `150*kcal*mol^-1`;

`C-=C`, `200*kcal*mol^-1`;

Are these data consistent with the argument just proposed?