Why is NO3 nonpolar but CIF3 is polar? I looked at the lewis structures, they look similar, but why is one opposite. also, when something is polar or non polar, my teacher said I should see which atom is more electronegativity is higher and draw arrows towards it on a lewis structure, then add "vectors" What does that mean? can you explain the question above with vectors. I tried doing it and the vectors don't cancel for both of them, but apparently it does cancel for NO3
The Correct Answer and Explanation is:
NO₃⁻ is nonpolar while ClF₃ is polar due to differences in their molecular geometry, which affects how the dipole vectors add up.
Even though both molecules have polar bonds due to differences in electronegativity between atoms, the shape of the molecule determines whether the dipole moments cancel out. Dipole moments (also called molecular dipoles) are represented by arrows pointing from the less electronegative atom toward the more electronegative atom. These arrows act like vectors, which have both direction and magnitude.
Nitrate Ion (NO₃⁻)
The nitrate ion, NO₃⁻, has a trigonal planar shape with three resonance structures. Each oxygen is equally electronegative and is double- or single-bonded in resonance with the central nitrogen atom. The molecule is symmetric, with bond angles of 120°. The dipole vectors from the nitrogen to each oxygen are equal in magnitude and are spaced evenly around the nitrogen. When you add these vectors using vector addition, they cancel out, resulting in no net dipole moment. Therefore, NO₃⁻ is nonpolar, despite containing polar N–O bonds.
Chlorine Trifluoride (ClF₃)
ClF₃ has a T-shaped molecular geometry. The central chlorine atom is surrounded by three bonded fluorine atoms and two lone pairs. The lone pairs occupy equatorial positions in a trigonal bipyramidal electron geometry, forcing the fluorines into a T-shape. Fluorine is more electronegative than chlorine, so each Cl–F bond has a dipole pointing toward fluorine. However, in this T-shape, the vectors do not cancel out completely. The vertical bond dipole remains unopposed, creating a net dipole moment. Thus, ClF₃ is polar.
Summary
Even if two molecules have similar atoms or polar bonds, their polarity depends on shape:
- NO₃⁻: Symmetric shape → dipoles cancel → nonpolar.
- ClF₃: Asymmetric shape → dipoles don’t cancel → polar.
Dipole arrows are added as vectors. When these vectors point evenly in opposite directions, they cancel. When the shape is uneven, like in ClF₃, they don’t, leading to polarity.
