Question

A molecule containing polar bonds is nonpolar, this is becaluse of (1) small sizes of atoms in the molecule (2) big sizes of atoms in the molecule (3) the atoms in it being highly electronegative (4) the vector cancellation of the bond moments

Short answer

The molecule is nonpolar due to vector cancellation of the bond moments.

Step-by-step solution

Understanding Polar and Nonpolar Molecules

A molecule is classified as polar or nonpolar based on the distribution of electrical charge over the atoms joined by the bond. Nonpolar molecules have an even distribution of electrical charge.

Identifying Bond Moments

In molecules with polar bonds, each bond has a dipole moment—a measure of the electrical polarity of the bond. For a molecule to be nonpolar despite having polar bonds, something must counteract these dipole moments.

Vector Cancellation of Bond Moments

For a molecule to be nonpolar, the vector sum of all bond dipole moments must cancel each other out. This means that, although individual bonds are polar, the overall spatial arrangement of these bonds leads to a net dipole moment of zero.

Conclusion

The correct explanation is that the molecule is nonpolar because of the vector cancellation of the bond moments. This means that the sum of all the polar bonds' dipole moments equals zero, making the molecule nonpolar.

Key concepts

polar molecules

Molecules are made up of atoms bonded together. When we talk about polar molecules, we're referring to molecules where there's an uneven distribution of electrical charge. This means one part of the molecule is slightly positive, while another part is slightly negative. This happens because different atoms have different abilities to attract electrons. For example, water (H₂O) is a classic polar molecule. Oxygen is more electronegative than hydrogen, so it pulls electrons closer to itself, making one side of the molecule more negative.
This separation of charges within the molecule creates a dipole moment, which we'll discuss in the next section.

• Polar molecules have regions of partial positive and negative charges.
• An uneven distribution of electrons creates these charged regions.
• The overall shape of the molecule often affects its polarity.

dipole moments

A dipole moment is a vector quantity that measures the separation of positive and negative charges in a molecule. It shows how strong and in which direction the polarity of a bond or a whole molecule points. Dipole moments arise in molecules with polar bonds, where electrons are not shared equally between the atoms.
Imagine a molecule like HCl (hydrogen chloride): chlorine is more electronegative and pulls the shared electrons towards itself, making one end of the molecule partially negative and the other end partially positive. The dipole moment points from the positive side to the negative side.

• Dipole moments can be seen as arrows pointing from positive to negative charges.
• They indicate the direction and magnitude of a molecule's polarity.
• A larger difference in electronegativity between atoms results in a stronger dipole moment.

vector cancellation

Vector cancellation is a key concept to understand why some molecules with polar bonds are nonpolar overall. Each dipole moment in a molecule can be represented as a vector. When these vectors are added together, their directions and magnitudes can cancel each other out.
Consider carbon dioxide (CO₂). It has two polar bonds, but the molecule is linear. The dipole moments of these bonds are equal in magnitude but opposite in direction, so they cancel each other out.
This results in a net dipole moment of zero, making CO₂ a nonpolar molecule despite having polar bonds.

• Vector cancellation happens when the directional dipole moments add up to zero.
• The 3D shape of a molecule is crucial for vector cancellation.
• Cancelling vectors result in a nonpolar molecule even if individual bonds are polar.