Question

Which contains both polar and non-polar bonds? (a) \(\mathrm{NH}_{4} \mathrm{Cl}\) (b) HCN (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (d) \(\mathrm{CH}_{4}\)

Short answer

The compound \(\mathrm{H}_{2}\mathrm{O}_{2}\) contains both polar and non-polar bonds.

Step-by-step solution

Understand Bond Types

To determine which compound contains both polar and non-polar bonds, we must first understand the difference. A polar bond occurs when there is a difference in electronegativity between the bonded atoms, resulting in an unequal sharing of electrons. Non-polar bonds occur when the electrons are shared equally between atoms of similar electronegativity.

Analyze Compound NH4Cl

The compound \(\mathrm{NH}_{4}\mathrm{Cl}\) consists of \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Cl}^{-}\). The N-H bond within the ammonium ion is polar due to the difference in electronegativity between nitrogen and hydrogen. However, this compound consists of ionic bonds between \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Cl}^{-}\), so it does not contain non-polar covalent bonds.

Analyze Compound HCN

In \(\mathrm{HCN}\), the bonds present are \(\mathrm{H-C}\) and \(\mathrm{C\equiv N}\). The \(\mathrm{H-C}\) bond is slightly polar because of the small difference in electronegativity, and the \(\mathrm{C\equiv N}\) bond is polar. Therefore, it does not contain both polar and non-polar covalent bonds.

Analyze Compound H2O2

In \(\mathrm{H}_{2}\mathrm{O}_{2}\), the structure includes \(\mathrm{O-O}\) and \(\mathrm{O-H}\) bonds. The \(\mathrm{O-H}\) bond is polar due to the significant electronegativity difference between oxygen and hydrogen, while the \(\mathrm{O-O}\) bond is non-polar because there is no difference in electronegativity between the two oxygen atoms.

Analyze Compound CH4

In \(\mathrm{CH}_{4}\), the bonds present are \(\mathrm{C-H}\). These bonds are considered to be non-polar due to the small difference in electronegativity between carbon and hydrogen. Thus, it only contains non-polar bonds.

Conclusion

After analyzing all the compounds, \(\mathrm{H}_{2}\mathrm{O}_{2}\) is the only compound that contains both polar and non-polar bonds due to its \(\mathrm{O-H}\) and \(\mathrm{O-O}\) bonds.

Key concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that refers to the ability of an atom to attract electrons towards itself in a chemical bond. Understanding this concept is crucial for determining if a bond is polar or non-polar. Generally, the greater the electronegativity difference between two bonded atoms, the more polar the bond will be.
For example, in

• The bond between hydrogen and oxygen, as seen in water (H₂O), involves a high difference in electronegativity; oxygen is much more electronegative than hydrogen.
• This causes the electrons to spend more time closer to the oxygen than the hydrogen, resulting in a polar covalent bond.
• On the other hand, a bond between two atoms of the same element, such as in an \( ext{O-O}\) bond found in H₂O₂, involves no electronegativity difference and is therefore non-polar.

By recognizing electronegativity differences, students can predict bond types and molecular polarity. Large differences often lead to ionic bonds, while smaller differences lead to polar covalent bonds.

Covalent Bonds

Covalent bonds are a type of chemical bond where two atoms share electrons. These can be further classified as polar or non-polar.
Polar covalent bonds occur when the sharing of electrons between atoms is unequal, caused by a difference in electronegativity.

• An example is the \( ext{O-H}\) bond in hydrogen peroxide (H₂O₂). The oxygen atom attracts the electrons more strongly than hydrogen, making the bond polar.

Non-polar covalent bonds occur when electrons are shared equally.

• An instance of this is the \( ext{O-O}\) bond, also found in H₂O₂, where both oxygen atoms have the same electronegativity and thus share the electrons equally.

The nature of covalent bonds affects the physical properties of the compound, such as solubility and melting and boiling points.

Ionic Bonds

Ionic bonds are different from covalent bonds in that they involve the complete transfer of electrons from one atom to another, leading to the formation of positive and negative ions. This typically happens when electronegativity differences between the atoms are very large.
A common example of an ionic bond can be seen in sodium chloride (NaCl).

• Here, sodium (Na) donates an electron to chlorine (Cl), creating positively charged \( ext{Na}^+\) and negatively charged \( ext{Cl}^-\) ions.
• This results in a strong electrostatic attraction between the opposite charges, forming a tight ionic lattice.

In our original exercise, while discussing \( ext{NH}_4 ext{Cl}\), it's important to note that the compound features ionic bonding between the ammonium ion (NH₄⁺) and chloride ion (Cl⁻). This is a prominent characteristic of compounds with large electronegativity differences, distinguishing them from their covalent counterparts.