How do protons differ from neutrons structurally?

Protons and neutrons differ structurally in their composition of quarks and their electric charge.

Protons and neutrons, collectively known as nucleons, are the fundamental particles that make up the nucleus of an atom. They are both baryons, a category of particles that are composed of three quarks. However, the type and arrangement of these quarks differ between protons and neutrons, leading to their distinct properties.

A proton is composed of two 'up' quarks and one 'down' quark. This combination gives the proton a positive electric charge. The 'up' quark carries a charge of +2/3, while the 'down' quark carries a charge of -1/3. Therefore, the total charge of a proton is +1. This positive charge is what allows protons to interact electromagnetically with electrons, which carry a negative charge.

On the other hand, a neutron is composed of one 'up' quark and two 'down' quarks. This arrangement results in a neutral charge, as the charges of the quarks cancel each other out. The 'up' quark's charge of +2/3 is negated by the combined charge of -2/3 from the two 'down' quarks, resulting in a total charge of 0. This lack of charge means that neutrons do not interact electromagnetically, but they do interact through the strong nuclear force, which holds the nucleus of an atom together.

The difference in quark composition and charge also leads to a slight difference in mass between protons and neutrons. Neutrons are slightly heavier than protons. This is because the 'down' quark is slightly heavier than the 'up' quark. However, this difference is so small that it is often negligible in many calculations.

In summary, while protons and neutrons are both composed of three quarks, the type and arrangement of these quarks differ. This results in protons having a positive charge and neutrons having a neutral charge. The difference in quark composition also leads to a slight difference in mass, with neutrons being slightly heavier than protons.