Question

Consider three hydrocarbon compounds: ethane, CH₃CH₃; ethene, CH₂CH₂; and

            ethyne, CHCH, in all of which the two carbon atoms are bonded to each other. Of the three, ethyne has the _____________ carbon-carbon bond.

A. longest and strongest                   B. shortest and weakest

C. shortest and strongest                   D. longest and weakest

Answer 1

Bond Length (^OA​)

Hybridization Bond Length

sp3–sp3    1.20

sp2–sp2 H₂C=CH₂ 1.34

sp–sp H₃C-CH₃ 1.54

Bond Strengths (kcal/mol)

sp3–sp3 198 Kcal/mol

sp2–sp2 H₂C=CH₂ 145 Kcal/mol

sp–sp H₃C-CH₃ 81 Kcal/mol

So from above data we can see that ethyne has Shortest and Strongest bond.

We know that know that S orbitals hold electrons more tightly to nucleus than P orbitals. An sp orbital is composed of one s orbital and one p orbital, and thus it has 50%  s character and 50% p character. where as sp2 orbitals and sp3 orbital contains 33% s character and 67% p character, and 25% s character and 75% p character. respectively. Because of their spherical shape, 2s orbitals are smaller, and hold electrons closer and ‘tighter’ to the nucleus, compared to 2p orbitals. Hence acetylene or ethyne has strongest and shortest bond.

sp3 = 25% s character, 75% p character

sp2 = 33% s character, 66% p character

sp = 50% s character, 50% p character-----most electro neagtive than CH2-CH2 and CH4.