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

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Atoms were developed after the big Bang 13.7 billion years ago. As the hot, dense new universe cooled, conditions became suitable for quarks and also electrons to form. Quarks came together to form protons and neutrons, and these particles merged into nuclei. This all took location within the first couple of minutes the the universe"s existence, follow to CERN.

It took 380,000 years for the world to cool sufficient to slow-moving down the electron so that the nuclei could record them to kind the very first atoms. The earliest atoms were mostly hydrogen and helium, which room still the most abundant facets in the universe, according to Jefferson Lab. Gravity ultimately caused clouds the gas to coalesce and form stars, and heavier atoms were (and quiet are) produced within the stars and 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 extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has actually a radius 10,000 times greater than the nucleus, follow to the Los Alamos nationwide Laboratory.

Protons and neutrons have about the very same mass. However, one proton is around 1,835 times an ext massive 보다 an electron. Atoms constantly have one equal variety of protons and also electrons, and also the variety of protons and also neutrons is normally the very same as well. Adding a proton to an atom renders a brand-new element, while adding a neutron provides an isotope, or more heavier version, of that atom.


The nucleus was discovered in 1911 through Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford proposed the surname proton for the positively fee particles that the atom. He additionally theorized that there to be a neutral particle within the nucleus, which James Chadwick, a brother physicist and student that Rutherford"s, had the ability to confirm in 1932.

Virtually all the massive of an atom resides in its nucleus, according to Chemistry LibreTexts. The protons and neutrons that comprise the cell nucleus are approximately the same mass (the proton is contempt less) and have the same angular momentum, or spin.

The nucleus is held together through the strong force, one of the four an easy forces in nature. This force in between the protons and neutrons overcomes the repulsive electrical force that would certainly otherwise push the proton apart, follow to the rules of electricity. Part atomic nuclei space unstable since the binding force varies for various atoms based upon the dimension of the nucleus. This atoms will certainly then decay into other elements, such as carbon-14 decaying right into nitrogen-14.


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


Protons room positively fee particles found within atom nuclei. Rutherford discovered them in experiments with cathode-ray tubes the were conducted in between 1911 and 1919. Proton are around 99.86% as huge as neutrons.

The number of protons in an atom is unique to each element. For example, carbon atoms have six protons, hydrogen atoms have one and also oxygen atoms have actually eight. The variety of protons in one atom is referred to as the atomic number of that element. The variety of protons additionally determines the chemical actions of the element. Elements are i ordered it in the routine Table the the elements in bespeak of raising atomic number.

Three quarks comprise each proton — 2 "up" quarks (each through a two-thirds confident charge) and one "down" quark (with a one-third an adverse charge) — and also they are hosted together by other subatomic particles referred to as gluons, which room massless.


Electrons space tiny compared to protons and neutrons, end 1,800 times smaller sized than one of two people a proton or a neutron. Electron are around 0.054% as enormous as neutrons, according to Jefferson Lab.

Joseph man (J.J.) Thomson, a brother physicist, uncovered the electron in 1897, follow to the Science background Institute. Originally known as "corpuscles," electrons have a an unfavorable charge and are electrically attracted to the positively fee protons. Electrons surround the atom nucleus in pathways referred to as orbitals, an idea the was placed forth through Erwin Schrödinger, an Austrian physicist, in the 1920s. Today, this version is recognized as the quantum design or the electron cloud model. The inside orbitals neighboring the atom are spherical but the outer orbitals room much much more complicated.

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


The neutron"s existence was theorized by Rutherford in 1920 and discovered by Chadwick in 1932, according to the American physics Society. Neutron were discovered during experiments as soon as atoms to be shot in ~ a slim sheet of beryllium. Subatomic particles with no fee were exit – the neutron.

Neutrons are uncharged particles found within all atomic nuclei (except because that hydrogen). A neutron"s fixed is slightly bigger than that of a proton. Like protons, neutrons are likewise made that quarks — one "up" quark (with a hopeful 2/3 charge) and two "down" quarks (each v a an adverse one-third charge).

History the the atom

The theory of the atom days at the very least as far earlier as 440 B.C. Come Democritus, a Greek scientist and philosopher. Democritus many likely constructed his theory of atom upon the work of past philosophers, follow to Andrew G. Valve Melsen, author of "From Atomos to Atom: The history of the principle Atom" (Duquesne university Press, 1952).

Democritus" explanation of the atom starts with a stone. A stone cut in fifty percent gives two halves the the exact same stone. If the rock were come be repeatedly cut, at some point there would exist a piece of the stone little enough that it could no longer be cut. The term "atom" originates from the Greek word for indivisible, which Democritus concluded have to be the suggest at i beg your pardon a gift (any type of matter) cannot be divided any type of more.

His explanation consisted of the principles that atom exist separately from each other, the there are an limitless amount of atoms, that atoms are able come move, the they can combine together to create matter yet do no merge to end up being a brand-new atom, and also that they can not be divided, according to universe Today. However, since most theorists at the time — particularly the an extremely influential Aristotle — thought that all matter was developed from earth, air, fire and also water, Democritus" atomic concept was put aside.

John Dalton, a brothers chemist, developed upon Democritus" principles in 1803 when he put forth his very own atomic theory, according to the chemistry room at Purdue University. Dalton"s theory consisted of several principles from Democritus, such together atoms space indivisible and also indestructible and that various atoms form together to develop all matter. Dalton"s additions to the theory had the adhering to ideas: the all atom of a specific element to be identical, the atoms of one element will have various weights and also properties 보다 atoms of one more element, the atoms can not be created or destroyed and that issue is created by atom combining in simple whole numbers.

Thomson, the brothers physicist who discovered the electron in 1897, confirmed that atoms deserve to be divided, according to the chemical Heritage Foundation. He was able to determine the presence of electrons by studying the properties of electrical discharge in cathode-ray tubes. Follow to Thomson"s 1897 paper, the rays were deflected within the tube, which showed that there was something the was negative charged within the vacuum tube. In 1899, Thomson released a summary of his version of the atom, generally known as the "plum pudding model." one excerpt the this record is found on the Chem Team site. Thomson"s version of the atom consisted of a large number of electrons suspended in miscellaneous that produced a confident charge giving the atom an all at once neutral charge. His model resembled plum pudding, a well-known British dessert that had raisins exposed in a round cake-like ball.

The following scientist to further modify and development the atomic version was Rutherford, that studied under Thomson, according to the chemistry department at Purdue University. In 1911, Rutherford published his variation of the atom, which contained a positively charged nucleus orbited through electrons. This model developed when Rutherford and also his assistants fired alpha corpuscle at thin sheets of gold. An alpha fragment is made up of 2 protons and also two neutrons, all held together by the same solid nuclear force that binds the nucleus, according to the Jefferson Lab.

The scientists noticed the a small percentage of the alpha particles were scattered in ~ very big angles come the initial direction of movement while the majority passed right through fixed disturbed. Rutherford had the ability to approximate the dimension of the cell core of the yellow atom, finding the to it is in at the very least 10,000 times smaller than the size of the whole atom with much of the atom being empty space. Rutherford"s model of the atom is tho the basic model the is supplied today.

Several other scientists furthered the atom model, consisting of Niels Bohr (built top top Rutherford"s version to encompass properties that electrons based upon the hydrogen spectrum), Erwin Schrödinger (developed the quantum version of the atom), Werner Heisenberg (stated the one cannot know both the position and also velocity of one electron simultaneously), and also Murray Gell-Mann and also George Zweig (independently developed the concept that protons and also neutrons were written of quarks).

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