Ionic atmosphere
Solutions of electrolytes are non‐ideal at relatively
low concentrations. The activities of ions in solution
is relatively large compared to neutral compounds.
Ions interact through a Coulombic potential that
varies as 1/r (r is the distance between ions). Neutral
solutes interact through London dispersion forces
that vary as 1/r6. The greater the charge on the ions
the larger the deviations from ideality. For example,
per mole of CaCl2 dissolved the deviation from ideal
behavior is larger than for NaCl due to the 2+ charge
of calcium ion. These considerations lead to the
concept of an ionic atmosphere.