The potassium bromide (KBr) molecule has an electric dipole moment of 3.50 × 10^-29  C⋅m. The molecule has a dipole moment because the lone 4s electron of the potassium atom spends much of its time orbiting the bromine nucleus (and thereby filling the 4p shell of bromine) – leaving the potassium atom positively charged and the bromine atom negatively charged (this is called “ionic bonding”).  
 
(a) Assuming for the moment that the potassium 4s electron spends all of its time orbiting the bromine nucleus, use the known dipole moment to calculate the physical separation between the potassium and bromine nuclei in the molecule.  
 
(b) The actual separation between the potassium and bromine nuclei is 0.282 nm  (2.82 × 10 -10 m). Use this value to describe the nature of the ionic bond between the atoms – what are the effective charges of the potassium and bromine atoms in the molecule, and how do these compare with the assumption made in (a)?