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MCAT Content / Atomic Nucleus / Nuclear Forces Binding Energy 2

### Nuclear forces, binding energy

Topic: Atomic Nucleus

The nuclear force is the force that is responsible for the binding of protons and neutrons into atomic nuclei.

The nuclear force is the force between two or more parts of atomic nuclei. The parts are neutrons and protons, which collectively are called nucleons. The nuclear force is responsible for the binding of protons and neutrons into atomic nuclei. The nuclear force is powerfully attractive at distances of about 1 femtometer (fm), rapidly decreases to insignificance at distances beyond about 2.5 fm, and becomes repulsive at very short distances less than 0.7 fm. The nuclear force is a strong interaction that binds together particles called quarks into nucleons.

To disassemble a nucleus into unbound protons and neutrons would require working against the nuclear force. Conversely, energy is released when a nucleus is created from free nucleons or other nuclei—known as the nuclear binding energy. The binding energy of nuclei is always a positive number since all nuclei require net energy to separate into individual protons and neutrons. Because of mass-energy equivalence (i.e., Einstein’s famous formula E=mc2), releasing this energy causes the mass of the nucleus to be lower than the total mass of the individual nucleons (leading to “mass deficit”). Binding energy is the energy used in nuclear power plants and nuclear weapons.

Key Points

• The nuclear force is the force that is responsible for the binding of protons and neutrons.

• The nuclear force is insignificance at distances beyond about 2.5 fm, repulsive at very short distances less than 0.7 fm.

• The binding energy of nuclei is always a positive number while the mass of an atom ‘s nucleus is always less than the sum of the individual masses of the constituent protons and neutrons when separated.

Key Terms

nucleus: the massive, positively charged central part of an atom, made up of protons and neutrons

quark: in the Standard Model, an elementary subatomic particle that forms matter. Quarks are never found alone in nature but combine to form hadrons, such as protons and neutrons

nuclear force: a force that acts between the protons and neutrons of atoms

nuclear binding energy: the minimum energy that would be required to disassemble the nucleus of an atom

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