What Is the Dipole Moment and How Does It Affect Polarity?

TL;DR

The molecule with carbon-fluorine bonds has the largest dipole moment, because its highly polar C-F bonds (electronegativity difference 1.5) do not cancel out. By contrast, carbon tetrabromide (CBr4), carbon dioxide (CO2), and 1,3,5-trichlorobenzene are all nonpolar because their bond dipoles cancel by symmetry. A bond only counts as polar when the electronegativity difference is 0.5 or greater. Read on to see how drawing vector arrows shows which dipoles cancel and which survive.

Transcript

number 10. which molecule has the largest dipole moment is it A B C or D well let's start with answer Choice a carbon Tetra bromide cbr4 carbon has an electronegativity value of 2.5 whereas bromine has an eon value of 2.8 the electronegativity difference is 0.3 in order for a bond to be polar the Electoral negativity difference has to be equal to o... Read More

Key Insights

• 🫀 The electronegativity difference between the atoms in a molecule determines the polarity of the bonds and, consequently, the dipole moment.
• ❓ In nonpolar molecules, the dipole moments from the bonds cancel out due to the symmetry of the molecule.
• 🐻‍❄️ Polar molecules have a net dipole moment because the dipole moments do not cancel out.
• 😥 The dipole moment can be determined by drawing arrows pointing toward the more electronegative atom in each bond.
• ❓ Carbon tetrabromide and 1,3,5-trichlorobenzene have nonpolar dipole moments due to the cancellation of dipole moments from the bonds.
• 🐻‍❄️ Carbon dioxide has polar bonds, but the dipole moments cancel out, resulting in a nonpolar dipole moment.
• 🐻‍❄️ Carbon fluoride has the largest dipole moment among the given molecules because the polar carbon-fluorine bonds do not cancel out.

Questions & Answers

Q: Which molecule has the largest dipole moment?

The molecule containing carbon-fluorine bonds has the largest dipole moment. The C-F bond is highly polar, with an electronegativity difference of 1.5 (fluorine is 4.0, carbon is 2.5). Its bond dipoles do not cancel, so the molecule keeps a net dipole moment above zero, making it polar. The other choices (CBr4, CO2, and 1,3,5-trichlorobenzene) all cancel to zero.

Q: Is carbon tetrabromide (CBr4) polar or nonpolar?

Carbon tetrabromide is nonpolar, with a dipole moment of zero. Carbon (2.5) and bromine (2.8) differ by only 0.3, so the C-Br bonds are relatively nonpolar to begin with. On top of that, all four outer atoms are identical and the tetrahedral shape points the small dipole arrows in opposing directions, so they cancel completely.

Q: Why is carbon dioxide (CO2) nonpolar even though its bonds are polar?

The carbon-oxygen bond is highly polar because oxygen's electronegativity (3.5) exceeds carbon's by 1.0. However, CO2 has two C-O bonds pointing in exactly opposite directions, so their dipole moments cancel. The result is no net dipole moment, making the overall molecule nonpolar.

Q: Why does 1,3,5-trichlorobenzene have a nonpolar dipole moment?

Each carbon-chlorine bond is polar, since chlorine (3.0) and carbon (2.5) differ by 0.5, right at the polar threshold. When you treat the three C-Cl dipoles as vectors, the x-components cancel against each other and the y-components add but then cancel against the top vector. Because all x- and y-components cancel, the net dipole moment is zero.

Q: What electronegativity difference makes a bond polar?

A bond is considered polar when the electronegativity difference between the two atoms is 0.5 or greater. Below that, the bond is treated as relatively nonpolar, though a small partial charge can still exist. For example, the C-Br difference of 0.3 is nonpolar, while the C-Cl difference of 0.5 sits right on the threshold.

Q: How do you determine a molecule's overall dipole moment?

Draw an arrow for each bond pointing toward the more electronegative atom, with the arrow length reflecting the size of the electronegativity difference. Then treat the arrows as vectors and add their x- and y-components. If all the components cancel, the net dipole moment is zero and the molecule is nonpolar; if they do not cancel, the molecule is polar.

Q: What electronegativity values are used in these examples?

The video uses carbon at 2.5, bromine at 2.8, chlorine at 3.0, oxygen at 3.5, and fluorine at 4.0. Subtracting carbon's value gives bond differences of 0.3 for C-Br, 0.5 for C-Cl, 1.0 for C-O, and 1.5 for C-F, which is why the fluorine-containing molecule ends up the most polar.

Summary & Key Takeaways

• Carbon tetrabromide (CBR4) has a nonpolar dipole moment because the electronegativity difference between carbon and bromine is relatively small, canceling out the dipole moments.

• Carbon dioxide (CO2) has polar bonds, but the dipole moments cancel out due to the opposite direction of the two carbon-oxygen bonds.

• 1,3,5-trichlorobenzene has a nonpolar dipole moment because the dipole moments from the carbon-chlorine bonds cancel each other out.

• Carbon fluoride (CF4) has the largest dipole moment among the given molecules due to the polar carbon-fluorine bonds, which do not cancel out.