Protons are subatomic particles with positive electric charge that can be found inside the atomic nucleus of all the atoms in the known universe.
All the elements in the periodic table have their own atomic number that is unique and represents the number of protons that are located in their atomic nucleus.
Proton – Definition
Protons are subatomic particles that are located inside the atomic nucleus of all the atoms in the universe and have a positive charge (+1 or 1,602 x 10-19 coulombs) and an atomic mass of 1.6726231*10-27 kg.
The positive charge (+1) of the proton is the opposite charge of the electron (-1) and is believed to be made by the type and the number of quarks forming the proton and their charge.
Electrons are also subatomic particles (much smaller than protons and neutrons) that are bound to the atomic nucleus or can be found freely (without being attached to any atomic nucleus).
The nucleus of the atom
Protons and neutrons are both located in the atomic nucleus and maybe this is the reason why they are called nucleons.
All nucleons (protons and neutrons located inside the atomic nucleus) are composed of three quarks.
A proton has two Up quarks, with 2/3 positive charge each, and one Down quark with a negative 1/3 charge, which means that the proton has a positive charge of 1 (2/3 + 2/3 + -1/3 = 4/3 +-1/3 = 3/3 = 1).
The other subatomic particle in the atomic nucleus is the neutron, which is made up of two Down quarks with the same 1/3 negative charge each and one Up quark with a positive 2/3 charge (-1/3 + -1/3 + 2/3 = 0).
The correspondent subatomic particle of the proton is the antiproton, which is similar to the proton but with a negative charge.
The proton is considered a stable particle by itself, but in the case of a radioactive decay, we can see (rarely) free protons being emitted and also free neutrons released in other disintegrations.
The free protons released this way can pick up an electron to become a neutral hydrogen isotope, which will react chemically with ease.
Free protons can be found in different types of plasma, in solar wind and also in cosmic rays.
History Of The Proton
In 1815, after a simplistic interpretation of earlier values of the atomic weights, William Prout proposed that all atoms are composed of hydrogen atoms (hydrogen has the symbol 1 in the periodic table because it has only one proton in its atomic nucleus).
Prout decided to name the particles “protyles”.
The proposal, based on his simplistic interpretation was disproved later.
In 1886 (after more than seven decades), Eugen Goldstein has discovered the anode rays (canal rays), and showed that they are particles (ions) with positive charge being produced from different gases.
By changing the type of gas in the tubes, Goldstein observed that the particles have a different charge-to-mass ratio, which meant that they cannot be identified using a single particle.
Negative electrons
However, negative electrons were discovered in 1887 by J. J. Thomson.
Wilhelm Wien discovered in 1889 that hydrogen ion is the particle with the highest charge-to-mass ratio present in ionized gases.
In 1917 (the experiments were reported only in 1919), Rutherford showed that the hydrogen nucleus is present in other atomic nuclei, which is a result that lead to the discovery of the protons.
Rutherford showed signs of hydrogen nuclei in pure nitrogen gas by bombarding the air (containing mostly nitrogen) with alpha particles.
Rutherford determined this way that hydrogen can only come from nitrogen and this is the reason why nitrogen must contain hydrogen nuclei.
However, during the bombarding process with alpha particles, a nucleus of hydrogen disintegrated due to the impact with the alpha particle, and formed an isotope of oxygen (oxygen-17).
This has proven that the hydrogen nucleus is present in other atomic nuclei of other chemical elements as an elementary particle, and Rutherford called the particle proton.
Rutherford first thought to name the new particle discovered with the word ‘protyle’ as proposed by Prout in 1815.
However, the final name for the particle was decided to be “proton”, which in Greek is the word for “first” (πρῶτον).
How Can Protons Be Described?
Protons like electrons, neutrons and quarks have spin 1/2 and are classified as baryons, which means that they represent a sub-type of hadrons (a composite particle made of two or three quarks held together by the strong nuclear force).
The strong nuclear force is the same force that keeps together protons and neutrons inside the atomic nucleus.
A hydrogen isotope is a nucleus with one proton, while the heavier isotopes of hydrogen (deuterium and tritium) contain the same number of protons (one), but combined with one or two neutrons in the atomic nucleus.
These two heavy hydrogen isotopes (deuterium and tritium) represent the nuclear fuel used in the nuclear fusion reaction.
The other chemical elements present in the periodic table have a different number of protons and neutrons in the atomic nucleus.
The number of protons in the atomic nucleus
The number of protons in the atomic nucleus determines the chemical properties of the chemical element that is represented in the periodic table after the number of protons in its nucleus (symbol Z).
To find the isotopes of a chemical element, we need to know the number of neutrons (N) and the number of protons (Z) in its atomic nucleus.
To obtain the mass number (A) of the chemical element we need to sum the number of protons (Z) and the number of neutrons (N) in the atomic nucleus (Z + N = A).
The new isotope will have the same name as the chemical element in the periodic table and will be followed by its mass number (A).
What is an Antiproton?
A proton has its correspondent particle in antimatter called antiproton.
The equality of these two particles has been tested to one part in 108, and shows that the electric charge of a proton and antiproton must sum to zero, and they must have equal masses.
The equality of the charge-to-mass ratio of protons and antiprotons was tested (to one part in 6×109) by holding antiprotons in a Penning trap.
The magnetic moment of the antiprotons was also measured, but with error of 8×10−3 nuclear Bohr magnetons, and has shown to be equal and opposite to the magnetic moment of the proton.
