Question

A lithium-7 nucleus contains 3 protons and 4 neutrons. Nuclear physicists in an isolated nation use a non-standard definition of the kilogramme. They have the following data:

Mass of Lithium-7 = 1.84081E-26 kg
Mass of neutron = 2.6463E-27 kg
Mass of proton = 2.6427E-27 kg
Determine their value for the mass defect of Lithium-7

Answer 1

The mass defect of Lithium-7 is -1.052E-28 kg.

Step-by-step explanation:

The mass defect of an isotope is the difference between the actual mass of the isotope and the sum of the masses of its constituent protons and neutrons. In the case of lithium-7, we can calculate the mass defect by subtracting the sum of the masses of its 3 protons and 4 neutrons from the actual mass of lithium-7.

The mass of a proton is 2.6427E-27 kg, and the mass of a neutron is 2.6463E-27 kg. Therefore, the mass of 3 protons is 3 x 2.6427E-27 kg = 7.9281E-27 kg, and the mass of 4 neutrons is 4 x 2.6463E-27 kg = 1.05852E-26 kg.

The actual mass of lithium-7 is given as 1.84081E-26 kg. Therefore, the mass defect of lithium-7 can be calculated as:

mass defect = actual mass - sum of constituent masses

mass defect = 1.84081E-26 kg - (7.9281E-27 kg + 1.05852E-26 kg)

mass defect = 1.84081E-26 kg - 1.85133E-26 kg

mass defect = -1.052E-28 kg