# 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.

Mar 31, 2017

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 $\text{atom-atom vector}$, 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 ${H}_{3} C - C {H}_{3}$, ${H}_{2} C = C {H}_{2}$, and ${H}_{3} C \equiv C {H}_{3}$ are $1.54 \times {10}^{-} 10 \cdot m$, $1.34 \times {10}^{-} 10 \cdot m$, and $1.21 \times {10}^{-} 10 \cdot m$.

And $C - C$ bond energies:

$C - C :$, $84 \cdot k c a l \cdot m o {l}^{-} 1$;

$C = C$, $150 \cdot k c a l \cdot m o {l}^{-} 1$;

$C \equiv C$, $200 \cdot k c a l \cdot m o {l}^{-} 1$;

Are these data consistent with the argument just proposed?