I think I may have found one check this link out http://www.chem.ucla.edu/~harding/tutor ... charge.pdf
"(The rare exception is a pure
covalent bond between two identical atoms such as in molecular chlorine, Cl-Cl.)
Because of this uneven sharing atoms have fractional, rather than integer, charges.
Calculations to determine
exact electron distribution and atomic charges require complex
computer programs and often many hours of computer time. "
also chek out https://study.com/academy/lesson/calcul ... rmula.html
"An exception that we need to take note of is for Helium (He). It is in group 18; however, it has only 2 valence electrons because its maximum number of electrons is 2. "
-Jimmy lira 1g