Atoms consists a nucleus do of protons and neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms are the simple units that matter and also the specifying structure the elements. The term "atom" originates from the Greek word for indivisible, because it was when thought that atoms to be the smallest points in the universe and also could not be divided. Us now recognize that atoms are made up of 3 particles: protons, neutrons and also electrons — which space composed of even smaller particles, such together quarks.

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Atoms were produced after the huge Bang 13.7 billion years ago. As the hot, dense brand-new universe cooled, conditions became perfect for quarks and also electrons to form. Quarks came with each other to type protons and neutrons, and also these particles merged into nuclei. This every took place within the first couple of minutes that the universe"s existence, according to CERN.

It took 380,000 years because that the cosmos to cool sufficient to slow down the electrons so the the nuclei could catch them to kind the an initial atoms. The earliest atoms were generally hydrogen and also helium, which are still the most abundant facets in the universe, follow to Jefferson Lab. Gravity ultimately caused clouds that gas to coalesce and type stars, and also heavier atoms to be (and quiet are) created within the stars and sent transparent the universe once the star explosive (supernova).

Atomic particles

Protons and also neutrons space heavier 보다 electrons and also reside in the nucleus at the center of the atom. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has actually a radius 10,000 times higher than the nucleus, follow to the Los Alamos nationwide Laboratory.

Protons and also neutrons have around the very same mass. However, one proton is about 1,835 times an ext massive 보다 an electron. Atoms always have an equal variety of protons and also electrons, and the number of protons and also neutrons is typically the very same as well. Including a proton come an atom renders a new element, while adding a neutron renders an isotope, or more heavier version, of the atom.


The nucleus was discovered in 1911 through Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford proposed the name proton because that the positively charged particles the the atom. He likewise theorized the there was a neutral bit within the nucleus, which James Chadwick, a brothers physicist and also student of Rutherford"s, was able to confirm in 1932.

Virtually all the fixed of an atom lives in the nucleus, according to Chemistry LibreTexts. The protons and also neutrons that make up the cell core are approximately the exact same mass (the proton is contempt less) and have the exact same angular momentum, or spin.

The cell nucleus is organized together by the solid force, among the four simple forces in nature. This force in between the protons and neutrons overcomes the repulsive electric force that would otherwise press the proton apart, follow to the rules of electricity. Part atomic nuclei are unstable because the binding pressure varies for various atoms based upon the size of the nucleus. These atoms will certainly then decay into other elements, such as carbon-14 decaying right into nitrogen-14.


Here"s a an easy drawing of the framework of one atom. (Image credit: Shutterstock)


Protons space positively charged particles discovered within atomic nuclei. Rutherford found them in experiments with cathode-ray tubes the were conducted between 1911 and 1919. Proton are around 99.86% as massive as neutrons.

The number of protons in one atom is distinctive to each element. For example, carbon atoms have actually six protons, hydrogen atoms have one and also oxygen atoms have actually eight. The variety of protons in an atom is referred to as the atomic variety of that element. The variety of protons also determines the chemical habits of the element. Elements are i ordered it in the regular Table the the facets in order of raising atomic number.

Three quarks consist of each proton — two "up" quarks (each with a two-thirds positive charge) and one "down" quark (with a one-third an unfavorable charge) — and they are held together by various other subatomic particles dubbed gluons, which room massless.


Electrons are tiny compared to protons and also neutrons, end 1,800 times smaller sized than either a proton or a neutron. Electrons are about 0.054% as substantial as neutrons, follow to Jefferson Lab.

Joseph man (J.J.) Thomson, a british physicist, found the electron in 1897, follow to the Science background Institute. Originally known as "corpuscles," electrons have actually a an unfavorable charge and also are electrically attractive to the positively charged protons. Electron surround the atomic nucleus in pathways called orbitals, one idea that was placed forth through Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this design is recognized as the quantum design or the electron cloud model. The inside orbitals bordering the atom room spherical but the outer orbitals space much more complicated.

An atom"s electron configuration describes the locations of the electron in a common atom. Making use of the electron configuration and principles of physics, chemists have the right to predict one atom"s properties, such together stability, boiling suggest and conductivity, follow to the Los Alamos national Laboratory.


The neutron"s presence was theorized by Rutherford in 1920 and also discovered by Chadwick in 1932, follow to the American physics Society. Neutron were found during experiments when atoms were shot in ~ a slim sheet that beryllium. Subatomic particles v no fee were exit – the neutron.

Neutrons are uncharged particles found within all atomic nuclei (except for hydrogen). A neutron"s mass is slightly bigger than the of a proton. Like protons, neutrons are likewise made of quarks — one "up" quark (with a optimistic 2/3 charge) and also two "down" quarks (each through a negative one-third charge).

History of the atom

The theory of the atom dates at the very least as far ago as 440 B.C. To Democritus, a Greek scientist and philosopher. Democritus most likely constructed his concept of atoms upon the occupational of previous philosophers, according to Andrew G. Van Melsen, author of "From Atomos come Atom: The history of the principle Atom" (Duquesne college Press, 1952).

Democritus" explanation the the atom begins with a stone. A rock cut in half gives 2 halves that the exact same stone. If the stone were to be continuously cut, in ~ some suggest there would certainly exist a item of the stone little enough that it might no longer be cut. The ax "atom" comes from the Greek word for indivisible, i m sorry Democritus concluded must be the suggest at i beg your pardon a gift (any form of matter) can not be divided any more.

His explanation had the ideas that atoms exist separately from every other, that there are an boundless amount that atoms, the atoms room able come move, that they can integrate together to develop matter yet do not merge to end up being a brand-new atom, and also that they can not be divided, according to world Today. However, due to the fact that most thinkers at the time — particularly the an extremely influential Aristotle — believed that all matter was produced from earth, air, fire and water, Democritus" atomic concept was put aside.

John Dalton, a brother chemist, constructed upon Democritus" principles in 1803 as soon as he put forth his very own atomic theory, according to the chemistry department at Purdue University. Dalton"s theory consisted of several ideas from Democritus, such together atoms space indivisible and indestructible and also that various atoms form together to develop all matter. Dalton"s enhancements to the theory included the complying with ideas: the all atom of a details element were identical, the atoms of one facet will have different weights and properties 보다 atoms of an additional element, the atoms cannot be created or destroyed and also that issue is formed by atom combining in simple whole numbers.

Thomson, the brothers physicist who found the electron in 1897, confirmed that atoms have the right to be divided, according to the chemistry Heritage Foundation. He was able to recognize the presence of electrons by examining the properties of electrical discharge in cathode-ray tubes. According to Thomson"s 1897 paper, the rays were deflected in ~ the tube, which showed that there was something that was negatively charged within the vacuum tube. In 1899, Thomson published a description of his variation of the atom, typically known as the "plum pudding model." an excerpt the this document is discovered on the Chem Team site. Thomson"s design of the atom included a large number of electrons suspended in other that developed a optimistic charge offering the atom an all at once neutral charge. His design resembled plum pudding, a popular British dessert that had raisins rely in a ring cake-like ball.

The following scientist to more modify and development the atomic model was Rutherford, that studied under Thomson, follow to the chemistry department at Purdue University. In 1911, Rutherford released his version of the atom, which had a positively fee nucleus orbited by electrons. This model occurred when Rutherford and also his assistants fired alpha corpuscle at slim sheets the gold. An alpha particle is consisted of of 2 protons and two neutrons, all held together by the same solid nuclear pressure that binding the nucleus, follow to the Jefferson Lab.

The scientists noticed the a tiny percentage of the alpha particles were scattered in ~ very huge angles come the original direction of movement while the bulk passed ideal through hardly disturbed. Rutherford had the ability to approximate the size of the cell nucleus of the yellow atom, finding the to be at least 10,000 times smaller than the size of the whole atom with lot of the atom being empty space. Rutherford"s version of the atom is quiet the basic model the is offered today.

Several other scientists advanced the atomic model, including Niels Bohr (built ~ above Rutherford"s version to include properties of electrons based on the hydrogen spectrum), Erwin Schrödinger (developed the quantum design of the atom), Werner Heisenberg (stated the one cannot understand both the position and also velocity of one electron simultaneously), and Murray Gell-Mann and George Zweig (independently arisen the theory that protons and neutrons were created of quarks).

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This post was update on Sept. 10, 2019, by Live scientific research contributor Traci Pedersen.