Chapter U2, Problem 15STP

Interpretation Introduction

Interpretation:

The bond polarity of the C-H bond in methane CH₄ needs to be identified.

Concept introduction:

The chemical bond or the polarity is found out by taking the difference of the electronegativity values of two bonded atoms. Non-polar bonds are formed for the elements having similar electronegativity values. Elements having difference in electronegativity values greater that equal to 2 will form polar bonds also known as ionic bond. The covalent polar bonds are formed between elements having $\Delta \text{EN}$ value between 0.3 and 1.7.

Answer to Problem 15STP

The correct answer is (D).

Explanation of Solution

Methane or CH₄ is the hydrocarbon which is generally used as a fuel. Methane is considered as non-polar. It is said to be non-polar because the electronegativities of C and H bonds are so close to each other. The values for C and H are: C = 2.55 and H = 2.20. Thus, the value of $\Delta \text{EN}$ is equal to 0.35 so it can’t be considered as polar molecule. The difference resembles to 3 percent of ionic character;thus, a C-H bond must have a small dipole moment.

So, the correct option is (D) which states that C-H bond polarity is quite small in CH₄ because of small electronegativity difference between hydrogen and carbon atom.