Question

Bond length between carbon-carbon in ethylene molecule is
A) 1.54 \[\mathop A\limits^0 \]
B) 1.35 \[\mathop A\limits^0 \]
C) 1.19 \[\mathop A\limits^0 \]
D) 2.4 \[\mathop A\limits^0 \]

Answer 1

Hint: When the two atoms are bonded, the average distance between their nuclei is called the bond length. There is a relation between bond length with bond strength, bond order, and dissociation energy of the bond.

Complete Step by Step Answer:
Let's understand the ethylene molecule in detail. The molecule of ethylene is made of two carbons and one double bond. The ethene formula is as follows: \[{{\rm{H}}_{\rm{2}}}{\rm{C}} = {\rm{C}}{{\rm{H}}_{\rm{2}}}\].

The VSEPR theory predicts the spatial positions of C and H atoms of the ethene and also the bond angle. Each atom of carbon is surrounded by three other atoms in the ethylene molecule, therefore, the geometry of the molecule is trigonal planar and the bond angle is of \[120^\circ \] .

The following diagram shows the molecule of ethylene.

Image: Ethylene molecule

So, we see that the Carbon-Carbon bond in the molecule of ethylene has a bond length of 133.9 or 134 pm or 1.34 \[\mathop A\limits^0 \] and the carbon-hydrogen bond has a bond length of 108.7 pm or 1.09 \[\mathop A\limits^0 \] .

Hence, option B is right which is close to 1.34 \[\mathop A\limits^0 \].

Note: It is to be noted that, there is the inverse relation between bond length and bond order that is, Bond length\[\alpha \dfrac{{\rm{1}}}{{{\rm{Bond}}\,{\rm{order}}}}\] . Therefore, the bond length of ethane is more than ethylene and the bond length of ethylene is more than ethyne. The bond lengths of a single bond, double bond, and triple bond are 154 pm, 134 pm, and 120 pm respectively.