electronegativity - ability of atom in a molecule to attract electrons
- used to see if bond will be nonpolar covalent, polar covalent, or ionic
- bond polarity - describes sharing of electrons between atoms
- nonpolar covalent bond - electrons shared equally (electronegativities equal)
- polar covalent bond - 1 atom attracts bonding electrons more than the other
- ionic bond forms when difference in electronegativity > 3
- based on ionization energy, electron affinity
- fluorine - most electronegative
- cesium - least electronegative
- in molecules, electron density (and negative charge) shift towards more electronegative atom
dipole moment - measure of dipole’s magnitude
- dipole - formed when electrical charges of opposite sign, equal magnitude separated by distance
- m = Qr
- m = dipole moment
- Q = electronic charge (unit e = 1.60 x 10-19 C)
- r = distance separating 2 atoms
- debyes (D) - unit equal to 3.34 x 10-30 coulomb-meters (C-m)
Calculate the dipole moment of HCl if the H and Cl are separated by 1.27Å
- Q = 1e = 1.60 x 10-19 C
- r = 1.27Å
- m = (1.60 x 10-19 C)(1.27Å)(10-10m/1.00Å)(1D/3.34 x 10-30 C-m)
- m = 6.08 D
In units of e, what is the charge on the atoms of a compound if they're separated by 2.74Å and have a measured dipole moment of 1.97 D?
- Q = m/r
- m = 1.97D = (1.97D)(3.34 x 10-30 C-m / D) = 6.5798 x 10-30 C-m
- r = 2.74Å = (2.74Å)(10-10m/1.00Å) = 2.74 x 10-10m
- Q = m/r = (6.5798 x 10-30 C-m) / (2.74 x 10-10m) = 2.40 x 10-20 C
- (2.40 x 10-20 C)(1 e / 1.60 x 10-19 C) = 0.150 e
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