Atoms covers a nucleus make of protons and neutrons orbited by electrons. (Image credit: Shutterstock)
Atoms space the simple units of matter and the defining structure that elements. The term "atom" originates from the Greek word because that indivisible, because it was as soon as thought the atoms to be the smallest points in the universe and also could no be divided. We now understand that atoms are consisted of of 3 particles: protons, neutrons and also electrons — which are composed of also smaller particles, such as quarks.

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

It take it 380,000 years because that the world to cool enough to slow down the electron so the the nuclei could catch them to kind the very first atoms. The earliest atoms were primarily hydrogen and also helium, which are still the many abundant elements in the universe, according to Jefferson Lab. Gravity eventually caused clouds the gas to coalesce and kind stars, and also heavier atoms were (and quiet are) produced within the stars and also sent throughout the universe when the star explosive (supernova).

Atomic particles

Protons and neutrons space heavier 보다 electrons and reside in the nucleus in ~ the facility of the atom. Electrons are incredibly lightweight and exist in a cloud orbiting the nucleus. The electron cloud has actually a radius 10,000 times better than the nucleus, follow to the Los Alamos national Laboratory.

Protons and also neutrons have roughly the very same mass. However, one proton is about 1,835 times more massive than an electron. Atoms always have an equal number of protons and also electrons, and the number of protons and also neutrons is typically the exact same as well. Including a proton come an atom makes a brand-new element, while adding a neutron makes an isotope, or more heavier version, of that atom.


The cell core was found in 1911 through Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford suggest the name proton for the positively charged particles the the atom. He also theorized the there to be a neutral fragment within the nucleus, i m sorry James Chadwick, a brother physicist and student that Rutherford"s, had the ability to confirm in 1932.

Virtually all the mass of an atom stays in that nucleus, follow to Chemistry LibreTexts. The protons and also neutrons that make up the cell nucleus are approximately the very same mass (the proton is slightly less) and have the very same angular momentum, or spin.

The cell nucleus is organized together through the solid force, among the four basic forces in nature. This force in between the protons and neutrons overcomes the repulsive electric force that would otherwise push the protons apart, according to the rule of electricity. Part atomic nuclei are unstable due to the fact that the binding force varies for various atoms based on the size of the nucleus. These atoms will certainly then decay into various other elements, such as carbon-14 decaying right into nitrogen-14.


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


Protons are positively fee particles found within atom nuclei. Rutherford uncovered them in experiments through cathode-ray tubes the were conducted between 1911 and 1919. Protons are about 99.86% as huge as neutrons.

The variety of protons in an atom is distinctive to each element. For example, carbon atoms have six protons, hydrogen atoms have actually one and oxygen atoms have eight. The number of protons in one atom is described as the atomic variety of that element. The variety of protons likewise determines the chemical habits of the element. Elements are arranged in the regular Table of the elements in bespeak of raising atomic number.

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


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

Joseph man (J.J.) Thomson, a brothers physicist, uncovered the electron in 1897, follow to the Science history Institute. Originally known as "corpuscles," electrons have actually a an adverse charge and also are electrically attracted to the positively fee protons. Electrons surround the atomic nucleus in pathways referred to as orbitals, one idea that was placed forth by Erwin Schrödinger, an Austrian physicist, in the 1920s. Today, this model is known as the quantum version or the electron cloud model. The within orbitals bordering the atom room spherical but the external orbitals room much much more complicated.

An atom"s electron configuration refers to the areas of the electrons in a common atom. Making use of the electron configuration and also principles that physics, chemists can predict an atom"s properties, such as 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 physics Society. Neutrons were uncovered during experiments once atoms were shot in ~ a slim sheet the beryllium. Subatomic particles through no charge were released – the neutron.

Neutrons are uncharged particles uncovered within every atomic nuclei (except because that hydrogen). A neutron"s fixed is slightly bigger than the of a proton. Favor protons, neutron are additionally made that quarks — one "up" quark (with a optimistic 2/3 charge) and also two "down" quarks (each through a an adverse one-third charge).

History of the atom

The theory of the atom dates at least as far ago as 440 B.C. To Democritus, a Greek scientist and also philosopher. Democritus most likely built his theory of atoms upon the occupational of past philosophers, follow to Andrew G. Valve Melsen, writer of "From Atomos to Atom: The background of the principle Atom" (Duquesne college Press, 1952).

Democritus" explanation that the atom begins with a stone. A rock cut in fifty percent gives 2 halves the the exact same stone. If the rock were to be consistently cut, in ~ some allude there would certainly exist a piece of the stone small enough that it can no much longer be cut. The ax "atom" originates from the Greek word because that indivisible, which Democritus concluded need to be the allude at i m sorry a being (any type of matter) cannot be divided any type of more.

His explanation consisted of the ideas that atom exist separately from each other, that there space an limitless amount of atoms, the atoms space able to move, that they can combine together to develop matter but do not merge to end up being a brand-new atom, and that they can not be divided, follow to world Today. However, since most theorists at the time — especially the really influential Aristotle — thought that all issue was created from earth, air, fire and water, Democritus" atomic concept was put aside.

John Dalton, a british chemist, constructed upon Democritus" concepts in 1803 when he placed forth his own atomic theory, according to the chemistry department at Purdue University. Dalton"s theory had several concepts from Democritus, such as atoms room indivisible and indestructible and that different atoms form together to produce all matter. Dalton"s additions to the theory contained the adhering to ideas: the all atoms of a particular element to be identical, that atoms that one aspect will have different weights and properties 보다 atoms of an additional element, that atoms can not be produced or destroyed and also that matter is created by atoms combining in basic whole numbers.

Thomson, the british physicist who discovered the electron in 1897, proved that atoms deserve to be divided, follow to the chemical Heritage Foundation. He was able to determine the existence of electrons by examining the nature of electrical discharge in cathode-ray tubes. Follow to Thomson"s 1897 paper, the rays to be deflected within the tube, which verified that there was something the was negative charged within the vacuum tube. In 1899, Thomson published a summary of his version of the atom, typically known as the "plum pudding model." an excerpt of this record is discovered on the Chem Team site. Thomson"s version of the atom included a big number of electron suspended in other that created a hopeful charge offering the atom an as whole neutral charge. His version resembled plum pudding, a famous British dessert that had actually raisins exposed in a round cake-like ball.

The next scientist to more modify and advance the atomic model was Rutherford, that studied under Thomson, according to the chemistry room at Purdue University. In 1911, Rutherford released his version of the atom, which had a positively charged nucleus orbited by electrons. This model arose when Rutherford and also his aides fired alpha corpuscle at thin sheets that gold. An alpha fragment is made up of two protons and also two neutrons, all organized together through the same solid nuclear force that binding the nucleus, follow to the Jefferson Lab.

The researchers noticed that a tiny percentage of the alpha particles to be scattered in ~ very large angles come the original direction of motion while the bulk passed ideal through hardly disturbed. Rutherford was able to approximate the size of the cell nucleus of the yellow atom, finding that to it is in at least 10,000 times smaller than the dimension of the entire atom with much of the atom being empty space. Rutherford"s model of the atom is tho the an easy model that is offered today.

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

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This short article was updated on Sept. 10, 2019, by Live scientific research contributor Traci Pedersen.