Permanent and Temporary Dipoles
Dipoles:
- A molecule with a positive end and a negative end
- When a molecule has a dipole it is called polarised
- There are several ways a molecule can become polarised
Permanent Dipoles:
- Permanent dipoles occur when a molecule has two atoms bonded together which have substantially different electro negatively, so that one atom attracts the shared electrons much more than the other
- Hydrogen chloride has a permanent dipole, because chlorine is much more electronegative than hydrogen, and so attracts the shared electrons more
- Molecules with a permanent dipole are called polar molecules
Instantaneous Dipoles:
- Some molecules do not possess a permanent dipole, because the atoms that are bonded together have the same, or very similar, electro negatively, so that the electrons are evenly shared
- Even though the molecule doesn’t have a permanent dipole, a temporary, or instantaneous dipole can arise
- Left on its own, this dipole only lasts for an instant before the swirling electron cloud changes its position, cancelling pout or even reversing the dipole
- However, if there are other molecules nearby, the instantaneous dipole may affect them and produce induced dipoles