Simulation · Chemistry · Class 11
Add up the bond dipoles
From the lesson Polarity of bonds and dipole moment in Chemical Bonding and Molecular Structure. Change the values and watch what happens.
Add up the bond dipolesChemistry · Class 11
The idea behind it
NCERT § "Polarity of Bonds"
- A bond between two identical atoms (H₂, O₂) is non-polar; when the atoms differ in electronegativity, the shared pair shifts towards the more electronegative atom and the bond becomes polar (as in HF).
- Dipole moment μ = charge × distance between the charge centres; it is a vector, drawn from the positive to the negative end in the convention chemists use (crossed arrow).
- The unit is the Debye: 1 D = 3.33564 × 10⁻³⁰ C m.
- A molecule's net dipole moment is the vector sum of its bond dipoles, so symmetry can cancel it: BeF₂, BF₃, CO₂, CH₄ and CCl₄ have zero dipole moment.
- Water is bent, so its two O–H bond dipoles add to a net value (about 1.85 D).
- NH₃ has a larger dipole moment than NF₃: in NH₃ the lone-pair moment adds to the N–H bond moments, while in NF₃ it opposes the N–F bond moments.
- Ionic bonds carry some covalent character too, and Fajans' rules say when it is larger: a small cation paired with a large anion, and a cation with a higher charge.
- Of two cations with the same size and charge, a transition-metal type cation with an (n−1)dⁿ ns⁰ configuration (for example Cu⁺, 3d¹⁰) polarises the anion more than one with a noble gas ns² np⁶ configuration.