Atoms consists a nucleus made of protons and neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms space the straightforward units of matter and the specifying structure that elements. The term "atom" originates from the Greek word for indivisible, since it was once thought the atoms to be the smallest points in the universe and also could no be divided. Us now understand that atom are consisted of of three particles: protons, neutrons and electrons — which room composed of also smaller particles, such together quarks.

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

It took 380,000 years because that the cosmos to cool sufficient to slow down the electron so that the nuclei could capture them to type the an initial atoms. The earliest atoms were mostly hydrogen and helium, which room still the most abundant elements in the universe, according to Jefferson Lab. Gravity at some point caused clouds that gas to coalesce and type stars, and heavier atoms were (and quiet are) produced within the stars and also sent transparent the universe as soon as the star exploded (supernova).

Atomic particles

Protons and neutrons are heavier than electrons and reside in the nucleus in ~ the center of the atom. Electrons are exceptionally lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times better 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 more massive than an electron. Atoms constantly have an equal variety of protons and electrons, and also the variety of protons and neutrons is generally the very same as well. Adding a proton to an atom provides a new element, while including a neutron renders an isotope, or heavier version, of that atom.


The cell core was discovered in 1911 through Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford proposed the surname proton because that the positively fee particles that the atom. He likewise theorized that there to be a neutral fragment within the nucleus, i m sorry James Chadwick, a brother physicist and also student of Rutherford"s, was able to confirm in 1932.

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

The cell nucleus is organized together through the solid force, one of the four an easy forces in nature. This force in between the protons and also neutrons overcomes the repulsive electric force that would otherwise press the proton apart, follow to the rules of electricity. Some atomic nuclei are unstable because the binding pressure varies for different atoms based on the dimension of the nucleus. This atoms will then degeneration into other elements, such as carbon-14 decaying right into nitrogen-14.


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


Protons space positively charged particles discovered within atom nuclei. Rutherford uncovered them in experiments v cathode-ray tubes the were conducted in between 1911 and 1919. Protons are around 99.86% as substantial as neutrons.

The variety of protons in an atom is distinctive to each element. Because that example, carbon atoms have actually six protons, hydrogen atoms have actually one and also oxygen atoms have eight. The variety of protons in an atom is described as the atomic variety of that element. The number of protons additionally determines the chemical habits of the element. Facets are arranged in the periodic Table the the aspects in bespeak of increasing atomic number.

Three quarks make up each proton — 2 "up" quarks (each through a two-thirds optimistic charge) and also one "down" quark (with a one-third negative charge) — and also they are hosted together by other subatomic particles called gluons, which space massless.


Electrons space tiny contrasted to protons and neutrons, end 1,800 times smaller than one of two people a proton or a neutron. Electrons are around 0.054% as huge as neutrons, follow to Jefferson Lab.

Joseph john (J.J.) Thomson, a british physicist, found the electron in 1897, follow to the Science history Institute. Originally well-known as "corpuscles," electrons have a an adverse charge and also are electrically attracted to the positively charged protons. Electron surround the atom nucleus in pathways dubbed orbitals, an idea the was put forth by Erwin Schrödinger, an Austrian physicist, in the 1920s. Today, this design is known as the quantum model or the electron cloud model. The inner orbitals bordering the atom room spherical but the outer orbitals room much much more complicated.

An atom"s electron configuration describes the areas of the electron in a usual atom. Making use of the electron configuration and principles the physics, chemists deserve to predict an atom"s properties, such together stability, boiling suggest and conductivity, according to the Los Alamos nationwide Laboratory.


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

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

History that the atom

The theory of the atom dates at least as far earlier as 440 B.C. To Democritus, a Greek scientist and also philosopher. Democritus many likely constructed his theory of atoms upon the work of previous philosophers, follow to Andrew G. Van Melsen, writer of "From Atomos to Atom: The background 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 the the same stone. If the stone were to be repeatedly cut, in ~ some point there would exist a piece of the stone little enough the it could no longer be cut. The hatchet "atom" originates from the Greek word because that indivisible, i beg your pardon Democritus concluded should be the suggest at i beg your pardon a gift (any form of matter) can not be divided any type of more.

His explanation included the concepts that atoms exist separately from every other, that there room an boundless amount that atoms, the atoms space able to move, that they can combine together to produce matter however do no merge to end up being a new atom, and that they cannot be divided, according to universe Today. However, because most thinkers at the time — specifically the really influential Aristotle — thought that all matter was developed from earth, air, fire and also water, Democritus" atomic concept was put aside.

John Dalton, a brother chemist, built upon Democritus" concepts in 1803 as soon as he placed forth his very own atomic theory, follow to the chemistry room at Purdue University. Dalton"s theory included several concepts from Democritus, such as atoms space indivisible and also indestructible and also that different atoms kind together to develop all matter. Dalton"s enhancements to the theory included the following ideas: that all atoms of a certain element to be identical, the atoms of one aspect will have various weights and properties 보다 atoms of an additional element, the atoms can not be produced or destroyed and also that matter is formed by atom combining in straightforward whole numbers.

Thomson, the brother physicist who uncovered the electron in 1897, proved that atoms can be divided, according to the chemical Heritage Foundation. He was able to recognize the presence of electron by studying the properties of electric discharge in cathode-ray tubes. Follow to Thomson"s 1897 paper, the rays to be deflected in ~ the tube, which showed that there was something the was negatively charged within the vacuum tube. In 1899, Thomson released a description of his version of the atom, frequently known as the "plum pudding model." an excerpt of this document is uncovered on the Chem Team site. Thomson"s design of the atom consisted of a huge number of electron suspended in other that created a hopeful charge offering the atom an all at once neutral charge. His design resembled plum pudding, a famous British dessert that had raisins rely in a ring cake-like ball.

The following scientist to more modify and advance the atomic version was Rutherford, who studied under Thomson, follow to the chemistry room at Purdue University. In 1911, Rutherford published his version of the atom, which had a positively charged nucleus orbited by electrons. This model emerged when Rutherford and his aides fired alpha particles at thin sheets of gold. An alpha bit is made up of 2 protons and also two neutrons, all hosted together by the same solid nuclear pressure that binding the nucleus, according to the Jefferson Lab.

The scientists noticed that a tiny percentage of the alpha particles to be scattered in ~ very big angles come the initial direction of movement while the bulk passed best through hardly disturbed. Rutherford was able to approximate the dimension of the nucleus of the yellow atom, finding it to be at the very least 10,000 times smaller sized than the dimension of the entire atom with much of the atom gift empty space. Rutherford"s version of the atom is quiet the simple model that is used today.

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

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This post was to update on Sept. 10, 2019, by Live science contributor Traci Pedersen.