A place to organise information in order to improve the article Chemical polarity.
Title says it all.
Classic examples are CF4 and CO2. The symmetry of these molecules causes the individual bond dipoles to cancel each other out. While carbon in CF4 is significantly more positive than in CH4, the partition of charge is not along any one line.
Some supposedly non-polar molecules actually have a small but real dipole moment, such as propane (μ = 0.084 ± 0.001 D [1]), presumably because the C-H and/or C-C bonds are slightly polarised. C and H do not have exactly the same electronegativity (2.55 vs. 2.20, according to Electronegativity, so C is δ− and H is δ+), which in any case depends on the atom's environment within the molecule. Electronegativity is not entirely fixed and transferable, although it usually seems to be approximately so.
Polar molecules experience dipole-dipole interactions which attract them to other nearby polar molecules.
This primarily electrostatic effect is a form of chemical bonding that is weaker than normal covalent and ionic bonds, but stronger than van der Waals forces.
How strong is it compared to hydrogen bonding?
“ | A polar molecule is one with a permanent electric dipole moment (HCl, O3 and NH3 are examples). | ” |
— Atkins' Physical Chemistry, 7th Edition, p. 461 |
“ | polar ...Physics & Chemistry having electrical or magnetic polarity. •(of a liquid, especially a solvent) consisting of molecules with a dipole moment. •(of a solid) ionic. |
” |
— Oxford Dictionary of English, p. 1360 |
Atkins, p. 462: ...only molecules belonging to the groups Cn, Cnv, and Cs may have a permanent electric dipole moment. For Cn and Cnv, that dipole moment must lie along the symmetry axis. Thus ozone, O3, which is angular and belongs to the group C2v, may be polar (and is), but carbon dioxide, CO2, which is linear and belongs to the group D∞h, is not.
A place to organise information in order to improve the article Chemical polarity.
Title says it all.
Classic examples are CF4 and CO2. The symmetry of these molecules causes the individual bond dipoles to cancel each other out. While carbon in CF4 is significantly more positive than in CH4, the partition of charge is not along any one line.
Some supposedly non-polar molecules actually have a small but real dipole moment, such as propane (μ = 0.084 ± 0.001 D [1]), presumably because the C-H and/or C-C bonds are slightly polarised. C and H do not have exactly the same electronegativity (2.55 vs. 2.20, according to Electronegativity, so C is δ− and H is δ+), which in any case depends on the atom's environment within the molecule. Electronegativity is not entirely fixed and transferable, although it usually seems to be approximately so.
Polar molecules experience dipole-dipole interactions which attract them to other nearby polar molecules.
This primarily electrostatic effect is a form of chemical bonding that is weaker than normal covalent and ionic bonds, but stronger than van der Waals forces.
How strong is it compared to hydrogen bonding?
“ | A polar molecule is one with a permanent electric dipole moment (HCl, O3 and NH3 are examples). | ” |
— Atkins' Physical Chemistry, 7th Edition, p. 461 |
“ | polar ...Physics & Chemistry having electrical or magnetic polarity. •(of a liquid, especially a solvent) consisting of molecules with a dipole moment. •(of a solid) ionic. |
” |
— Oxford Dictionary of English, p. 1360 |
Atkins, p. 462: ...only molecules belonging to the groups Cn, Cnv, and Cs may have a permanent electric dipole moment. For Cn and Cnv, that dipole moment must lie along the symmetry axis. Thus ozone, O3, which is angular and belongs to the group C2v, may be polar (and is), but carbon dioxide, CO2, which is linear and belongs to the group D∞h, is not.