Protons can be found in the nucleus of all atoms.
A proton is a subatomic particle found in the nucleus of all conventional atoms. The only place you can find matter without protons is in a neutron star or at the center of powerful particle accelerators. The proton has a positive charge, which balances the negative charge of the atoms, the electrons. If an atom has an imbalance of protons or neutrons, it stops being neutral and becomes a charged particle, also known as an ion.
Like protons, neutrons can be used by special microscopes to create images.
It is difficult to determine who, exactly, discovered the proton. Scientists theorized about the existence of positively charged particles after JJ Thomson’s discovery of the electron in 1897. However, Ernest Rutherford is often credited with the discovery based on his 1918 experiments.
Rutherford fired alpha particles, which are essentially electronless helium nuclei, into nitrogen gas. His detectors found the characteristic signature of hydrogen nuclei being produced. After some thought, he realized that these hydrogen nuclei could only come from nitrogen gas. This led to the theory that the nucleus of a hydrogen atom was an elementary particle, the proton, and that protons could be found in the nucleus of all atoms.
The properties of atoms are defined by the number of electrons, neutrons, and protons they have. However, the number of protons is the most significant variable. This variable is so important, in fact, that the number of protons in the nucleus of an atom is called the atomic number, and atoms are named by the number of protons they have.
The atomic number is the most physically relevant characteristic of an atom. Atoms with low atomic numbers are the most prevalent in the universe because they are the easiest to form. That is why hydrogen and helium are the most abundant elements in the universe.
In 1955, the proton’s evil twin, the antiproton, was discovered. Instead of having a positive charge, it has a negative charge. Like all antimatter, it explodes on contact with normal matter.
Protons are also a favorite among experimental physicists who like to accelerate them to significant fractions of the speed of light. Ballistic protons are responsible for many discoveries in the huge “particle zoo” that spawned 20th-century physics. Unlike their cousins the neutrons, protons are stable outside of an atomic nucleus, which makes them useful for experimental purposes.