Chapter U2.33, Problem 3E

Interpretation Introduction

Interpretation:

The reason for fewer hydrogen atoms in ${\text{C}}_{\text{2}}{\text{H}}_4$ than ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$ needs to be explained.

Concept introduction:

Organic compounds that contains only carbon and hydrogen atoms are said to be hydrocarbons. There are two types of hydrocarbons that is saturated and unsaturated hydrocarbon.

Saturated hydrocarbon: Those hydrocarbons which contains only single covalent bond, include alkanes. The amount of hydrogen is high compared to the amount of carbon. They are less reactive and are obtained from fossil animal and plant material.

Unsaturated hydrocarbon: Those hydrocarbons which contains multiple covalent bonds, include alkenes, alkynes, and aromatic. The amount of carbon is high compared to the amount of hydrogen. They are more reactive and are obtained from plant material.

Answer to Problem 3E

Due to the presence of double bond in ${\text{C}}_{\text{2}}{\text{H}}_4$, the number of hydrogen atoms is lesser in ${\text{C}}_{\text{2}}{\text{H}}_4$ than ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$.

Explanation of Solution

Alkanes are hydrocarbons that is they contain only carbon and hydrogens attached by single bonds only. The general formula for alkane is C_nH_{2n + 2}, where n is number of carbon atoms.

Alkenes are hydrocarbons that is they contain carbon and hydrogens attached by single bonds and presence of one or more double covalent bond between two carbon atoms. The general formula for alkene is C_nH_2n, where n is number of carbon atoms.

The structure of ${\text{C}}_{\text{2}}{\text{H}}_4$ and ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$ will be:

From the above structures, it is clear that. there is a presence of double bond in two carbon atoms in ${\text{C}}_{\text{2}}{\text{H}}_4$ whereas the bonds present in ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$ are single bond.

Due to the presence of double bond in ${\text{C}}_{\text{2}}{\text{H}}_4$, the two valences of C atom out of four are satisfied and the remaining two are satisfied by formation of two $\text{C-H}$ single bonds by each carbon atom. Whereas in ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$, the $\text{C-C}$ single bond satisfies only one valence of C atom out of four and the remaining three are satisfied by formation of three $\text{C-H}$ single bonds by each carbon atom.

Hence, due to the presence of double bond in ${\text{C}}_{\text{2}}{\text{H}}_4$, the number of hydrogen atoms is lesser in ${\text{C}}_{\text{2}}{\text{H}}_4$ than ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$.