Question

The molecule \(\mathrm{Cl}_{2}\) is nonpolar, but \(\mathrm{HCl}\) is polar. Explain.

Short answer

\( \text{Cl}_{2} \) is nonpolar due to equal sharing of electrons. \( \text{HCl} \) is polar due to unequal sharing of electrons.

Step-by-step solution

Understanding Polarity

Polarity in molecules is determined by the difference in electronegativity between atoms and the molecular geometry. If there is an unequal sharing of electrons, the molecule is polar due to partial charges.

Analyze \(\text{Cl}_{2}\)

\( \text{Cl}_{2} \) consists of two chlorine atoms with the same electronegativity. Since both atoms share electrons equally, there is no separation of charge. Thus, \( \text{Cl}_{2} \) is nonpolar.

Analyze \(\text{HCl}\)

\( \text{HCl} \) consists of a hydrogen atom and a chlorine atom. Chlorine has a higher electronegativity than hydrogen, causing an unequal sharing of electrons. This creates a dipole moment with partial negative charge on chlorine and partial positive charge on hydrogen. Thus, \( \text{HCl} \) is polar.

Conclusion

Since \( \text{Cl}_{2} \) has identical atoms with equal electronegativity it is nonpolar, whereas \( \text{HCl} \) has different atoms with unequal electronegativity, leading to polarity.

Key concepts

Electronegativity

Electronegativity is a measure of how strongly an atom attracts electrons in a bond. Each element has a specific electronegativity value. The higher the value, the stronger the pull on electrons.

In the molecule \(\text{Cl}_{2}\), both chlorine atoms have the same electronegativity. This means they attract electrons equally, resulting in even sharing of electrons. As a result, \(\text{Cl}_{2}\) is nonpolar.

However, in \(\text{HCl}\), chlorine has a higher electronegativity than hydrogen. Chlorine pulls electrons more strongly, causing an unequal sharing of electrons. This difference creates a partial negative charge on chlorine and a partial positive charge on hydrogen, making \(\text{HCl}\) polar.

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. It plays a crucial role in determining the polarity of a molecule.

In molecules where the central atom has identical atoms bonded symmetrically, the molecule can be nonpolar even if the bonds themselves are polar.

For example, in \(\text{CO₂}\), the molecule is linear with polar \(\text{C=O}\) bonds, but the polarities cancel out due to the symmetrical linear shape, making \(\text{CO₂}\) nonpolar.

On the other hand, the geometry of \(\text{HCl}\) is simple, as it's a diatomic molecule with only two atoms. There is no symmetry to cancel out the dipole, leading to a polar molecule.

Dipole Moment

A dipole moment occurs when there is a charge separation in a molecule. It is a vector quantity, involving both magnitude and direction of the charge difference.

Molecules with polar bonds have dipole moments. The greater the difference in electronegativity, the larger the dipole moment.

In \(\text{Cl}_{2}\), both atoms have the same electronegativity, so the electron distribution is equal, resulting in no dipole moment. This makes \(\text{Cl}_{2}\) nonpolar.

In \(\text{HCl}\), chlorine is more electronegative than hydrogen, creating a dipole with a partial negative charge on chlorine and a partial positive charge on hydrogen. This dipole moment makes \(\text{HCl}\) polar.

Understanding dipole moments helps explain why some molecules interact differently with electric fields and solvents.