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