Proton

A proton is a tiny particle found in the center of every atom. It has a positive electric charge, which pulls it toward electrons. Protons and neutrons make up the nucleus of an atom. The number of protons tells us what kind of element the atom is. For example, all hydrogen atoms have one proton, and carbon atoms have six protons.

The word "proton" comes from a Greek word meaning "first." Scientists found protons in the early 1900s while studying tiny particles. At first, protons seemed like simple building blocks of all matter. But we now know they are made of even smaller parts called quarks. A proton is made of three quarks: two up quarks and one down quark.

Protons are very important in science and medicine. They are used in special machines to help treat some kinds of cancer, in a process called proton therapy. They are also used in big research places like the Large Hadron Collider to learn about the basic nature of matter. Even though protons are very small, they help shape how everything in the universe is made and works.

Description

Protons are tiny particles with a positive charge. They are made of smaller parts called quarks. These quarks are held together by a strong force.

Protons and neutrons are the building blocks of the centers of atoms, called nuclei. The simplest atom, hydrogen, has just one proton in its center. Heavier atoms have more protons and neutrons in their nuclei.

History

Scientists have wondered what tiny parts make up atoms. In 1815, William Prout thought all atoms might be made of small pieces called "protyles."

Later, in 1886, Eugen Goldstein found special rays called canal rays. These rays carried a positive charge, unlike the negative electrons found earlier.

In 1919, Ernest Rutherford did experiments that showed a tiny part of the atom, which he called the proton. This helped scientists understand how atoms are built.

Occurrence

Protons are found in the center, or nucleus, of every atom. Free protons, which are not attached to electrons, can be found in places with very high energy or temperature, such as during thunderstorms or in plasmas. Most cosmic rays, which are high-energy particles from space, are made up of free protons. They can also come from certain types of radioactive decay.

Stability

Scientists are still trying to figure out if protons, tiny parts of atoms, stay the same forever or if they break down after a very long time. Right now, we think protons don't break down because we haven't seen it happen in experiments. Some ideas in physics say protons might break down, but if they do, it would take a very, very long time.

Protons can change into another tiny part called a neutron, but this usually needs extra energy. For example, when a proton meets an electron, it can turn into a neutron and send out a tiny particle called a neutrino. The opposite can also happen: a neutron can change back into a proton. This change is a kind of natural process called radioactive decay.

Quarks and the mass of a proton

In quantum chromodynamics, we learn that most of a proton's mass comes from special relativity. A proton's mass is much bigger than the total mass of its three tiny parts called quarks. The extra mass comes from the energy of the quarks and particles called gluons inside the proton.

Scientists study protons in different ways. One way looks at the mass of quarks by themselves, and another way looks at the mass when quarks are surrounded by gluons. These masses can be very different. The energy from the movement of quarks and gluons helps make up most of the proton's mass.

Charge radius

A proton is very small, about 8.4075 × 10⁻¹⁶ m. Scientists measure its size in different ways. One way uses how electrons bounce off protons. Another way uses a special atom made of a proton and a heavy particle called a muon. Because muons are heavier than electrons, they can show the proton's size more clearly.

There are still some questions about these measurements, and scientists are working to understand them better.

Pressure inside the proton

Inside a proton, there is a lot of pressure because it is made of tiny particles called quarks. These quarks are held together by other particles called gluons. In 2018, scientists said this pressure might be as high as 10³⁵ Pa, which is more than the pressure inside a neutron star. But there is debate about these numbers, and some think the pressure might actually be zero.

Charge radius in solvated proton, hydronium

When a proton is in water, it changes shape and forms a structure called hydronium. The size of this structure is used in special equations to understand how energy works when things mix with water.

Interaction of free protons with ordinary matter

When protons move through normal matter, they slow down and connect with electrons. This happens because protons have a positive charge and are pulled toward negatively charged electrons.

As protons lose energy, they can attach to atoms and form new chemical bonds. These bonded protons stay the same but become part of a new molecule. When this happens, the molecule is called "protonated" and it often acts like an acid. For example, when a proton joins a water molecule, it forms hydronium, which is a type of water molecule with a positive charge.

Proton in chemistry

In chemistry, the number of protons in an atom's nucleus is called the atomic number. This number tells us what element the atom is. For example, chlorine has an atomic number of 17, meaning every chlorine atom has 17 protons. The number of electrons in a neutral atom is the same as the number of protons, so a neutral chlorine atom has 17 electrons.

A proton can also be thought of as a hydrogen ion, which is just a single proton without any electrons. In water, protons join with water molecules to form groups like H₃O⁺. When acids and bases react, they often transfer protons — the acid gives a proton to the base.

Human exposure

Main article: Effect of spaceflight on the human body

See also: Proton therapy

The Apollo Lunar Surface Experiments Packages found that most particles from the solar wind are tiny particles called electrons and protons, almost in equal amounts.

Studies have looked at how protons, which are found during space travel, might affect human health. Scientists are learning more about how these particles might affect cells. They are also studying how spacecraft can stay safe when hit by these particles from space.

Antiproton

Main article: Antiproton

The rules of nature say that particles and their opposites, called antiparticles, should have very similar properties. Scientists have studied protons and their opposites, called antiprotons. They found that the charges of protons and antiprotons are exactly the same, and their masses are also almost exactly the same. Special tools can hold antiprotons still, and this helps scientists compare them very carefully. The tiny bits of magnet-like behavior in protons and antiprotons are almost exactly the same, but in opposite directions.