1. The problem statement, all variables and given/known data The difference between the mass of one oxygen atom and the sum of the masses of its parts is approx. 2.27 x 10^-28 kg. What is the binding energy that holds an oxygen atom together? (The charge on one electron is 1.6x10^-19 C). 2. Relevant equations E = mc^2 3. The attempt at a solution I started off with listing my knowns: mass = 2.27 x 10^-28 kg E = what we're solving for c = 3 x 10^8 m/s E = (2.27 x 10^-28)(3.8 x 10^8)^2 18.54 x 10^-14 = 1.85 x 10^-15 J To convert Joules to eV, I divide by the charge on one electron: (1.85 x 10^-15)/(1.6 x 10^-19) = 1.2 x 10^4 eV. My book says it's 1.2 x 10^8 eV but I don't know why.