# Finding the binding energy for lithium

## Homework Statement

Find the binding energy (in MeV) for lithium 3Li8 (atomic mass = 8.022486 u).

## Homework Equations

Binding energy = (#p)(mass proton) + (#n)(mass neutron) - (mass nuclei*c^2)

## The Attempt at a Solution

mass proton = 1.007825
mass neutron = 1.008665
Binding energy = (3)(1.007825) + (5)(1.008665) - (8.022486*(3e8)^2)
Binding energy = -7.22e17 J x 1 eV/1.602e-19 J = -4.506e36 eV x 1e-6 MeV / 1 eV = -4.506e30 MeV

## Answers and Replies

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Kurdt
Staff Emeritus
Science Advisor
Gold Member
Check your units please. Also your formula for binding energy is wrong. Check the c2's.

Oops, sorry I know I typed the formula wrong on here, but I did it the correct way on my homework... It's still telling me my answer is incorrect. :/

Astronuc
Staff Emeritus
Science Advisor
mass proton = 1.007825
mass neutron = 1.008665

are atomic mass units (amu). Be careful about mixing units.

If one is using c = 3 x 108 m/s, then one must use atomic masses in kgs.