The neutron is one of the most common particles of matter, and it is integral to the formation of every element other than hydrogen. Find out why.
Hydrogen is made up of a lone proton which may or may not be accompanied by an electron. When a single proton is paired with a neutron it is called deuterium (a single atom is called a deuteron), an isotope of hydrogen. An element is defined by the number of protons in its nucleus. For each element there are a specific number of protons, but an element can have a variable number of neutrons. The heavier the element, the more variations there tends to be. These variations are called isotopes.
Neutrons combine with protons to create heavier elements. Protons by themselves repel one another because they all have a positive electromagnetic charge, and like charges always repel. The neutron has no charge because it is made up of one "up" and two "down "quarks. An up quark carries a charge of +2/3, while a down quark carries a charge of -1/3. This adds up to a charge of 0. In contrast, a proton is made up of two up quarks, and one down quark, giving it a charge of +1. Interestingly, the up quark weighs about half as much as a down quark, so a neutron is slightly heavier than a proton. It is this difference in weight proportions that allow scientists to definitively identify different elements and isotopes.
The neutron does not have any charge at all, but it is still able to act as glue to hold the protons in a heavy nucleus together. How is this possible if neutrons do not have an opposite, negative charge?
Charge is not the only significant property of nuclear particles. Other forces are present, and the culprit here is the nuclear force, sometimes known as the residual strong force. Protons possess the nuclear force which make them mutually attractive over extremely short distances (the diameter of an atom). Neutrons also possess nuclear force, in virtually the same way that protons do. Even though two protons can be bound together with just the nuclear force, it is not very stable because the electromagnetic force is working in opposition. When neutrons are introduced, the nucleus becomes more stable. There is more nuclear force overall to counteract the electromagnetic force, and elements heavier than hydrogen and helium can form.
The nuclear force fades quickly with increasing distance. Elements with a larger nuclear diameter than Bismuth (83 protons) can't hold their nuclei together reliably. These elements tend to degrade radioactively, randomly radiating nuclear particles that come unglued, transforming the element to a more stable and smaller element.
