What is the mass defect of lithium? Assume the following:

Question

Atomic number of lithium = 3

Atomic mass of lithium = 7.0144 atomic mass units.

Mass of 1 proton = 1.0073 atomic mass units.

Mass of 1 neutron = 1.0087 atomic mass units.

A. 

0.0043 atomic mass units

B. 

0.0423 atomic mass units

C. 

3.0219 atomic mass units

D. 

4.0348 atomic mass units

E. 

7.0567 atomic mass units

Answer 1

Lithium has 3 protons and 4 neutrons (protons + neutrons = atomic mass of ~7)

Proton mass: 3 x 1.0073 = 3.0219 amu

Neutron mass: 4 x 1.0087 = 4.0348 amu

Sum of proton and neutron mass = 7.0567

Difference (mass defect) between actual and predicted mass = 7.0567 - 7.0144 = 0.0423 amu (answer B)