Calculate the mass defect for the isotope thorium-234

Mass defect is defined as the difference or discrepancy between the mass of the nucleons and the mass of the nucleus. the nucleons involved are the protons and neutrons. 
mp  = 1.6727 x 10-24 g = 1.007316 amumn = 1.6750 x 10-24 g = 1.008701 amu
mTh 234 = 234 g/mol = 234 amu

Th234 (protons = 90; neutrons = 144)
mass defect = mp*90 + mn *144 - 234
mass defect = 1.911384 amu