For a carbon-12 atom, take mₕ = 1.0078 u, mₙ = 1.0087 u and M(atom) = 12.0000 u. If the mass defect is Δm = N×10⁻³ u, find N.

Question

G1 Physics · Accepted Answer

For carbon-12, Z = 6, number of neutrons = 12−6 = 6. Using atomic masses, Δm = Zmₕ + Nmₙ − M(atom). Therefore, Δm = 6(1.0078) + 6(1.0087) − 12.0000. Now, 6(1.0078) = 6.0468, 6(1.0087) = 6.0522. Hence, Δm = 6.0468 + 6.0522 − 12.0000 = 0.0990 u = 99×10⁻³ u. Therefore N = 99.