Atoms covers a nucleus do of protons and also neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms room the an easy units that matter and the defining structure the elements. The hatchet "atom" comes from the Greek word because that indivisible, since it was as soon as thought the atoms to be the smallest points in the universe and could not be divided. We now know that atom are consisted of of 3 particles: protons, neutrons and also electrons — which room composed of also smaller particles, such together quarks.

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Atoms were developed after the large Bang 13.7 billion year ago. Together the hot, dense brand-new universe cooled, conditions became an ideal for quarks and electrons to form. Quarks came together to kind protons and also neutrons, and these particles an unified into nuclei. This all took place within the first couple of minutes the the universe"s existence, according to CERN.

It took 380,000 years for the universe to cool sufficient to slow down the electron so that the nuclei could record them to type the first atoms. The earliest atoms were generally hydrogen and helium, which space still the many abundant elements in the universe, follow to Jefferson Lab. Gravity eventually caused clouds of gas come coalesce and kind stars, and heavier atoms to be (and still are) created within the stars and sent throughout the universe when the star exploded (supernova).

Atomic particles

Protons and neutrons are heavier 보다 electrons and also 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 nationwide Laboratory.

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


The cell core was found in 1911 by Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford suggest the name proton because that the positively charged particles the the atom. He likewise theorized that there was a neutral bit within the nucleus, i beg your pardon James Chadwick, a brother physicist and student the Rutherford"s, had the ability to confirm in 1932.

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

The cell nucleus is held together by the solid force, one of the four straightforward forces in nature. This force in between the protons and also neutrons overcomes the repulsive electric force that would certainly otherwise push the protons apart, follow to the rules of electricity. Some atomic nuclei space unstable due to the fact that the binding force varies for different atoms based on the size of the nucleus. These atoms will then degeneration into various other elements, such together carbon-14 decaying into nitrogen-14.


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


Protons are positively charged particles uncovered within atom nuclei. Rutherford found them in experiments with cathode-ray tubes that were conducted between 1911 and also 1919. Proton are about 99.86% as massive as neutrons.

The variety of protons in one atom is distinct to each element. Because that example, carbon atoms have six protons, hydrogen atoms have actually one and also oxygen atoms have eight. The number of protons in one atom is described as the atomic number of that element. The number of protons additionally determines the chemical actions of the element. Aspects are arranged in the periodic Table the the facets in order of increasing atomic number.

Three quarks consist of each proton — 2 "up" quarks (each through a two-thirds positive charge) and also one "down" quark (with a one-third an unfavorable charge) — and they are organized together by various other subatomic particles dubbed gluons, which are massless.


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

Joseph john (J.J.) Thomson, a brothers physicist, discovered the electron in 1897, follow to the Science history Institute. Originally recognized as "corpuscles," electrons have a an adverse charge and are electrically attracted to the positively fee protons. Electron surround the atomic nucleus in pathways called orbitals, an idea the was put forth by Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this version is known as the quantum version or the electron cloud model. The inner orbitals neighboring the atom space spherical however the outer orbitals space much an ext complicated.

An atom"s electron configuration refers to the locations of the electrons in a common atom. Utilizing the electron configuration and also principles the physics, chemists have the right to predict an atom"s properties, such as stability, boiling allude and conductivity, follow to the Los Alamos nationwide Laboratory.


The neutron"s visibility was theorized through Rutherford in 1920 and discovered through Chadwick in 1932, according to the American physics Society. Neutrons were uncovered during experiments when atoms to be shot in ~ a slim sheet of beryllium. Subatomic particles v no fee were exit – the neutron.

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

History of the atom

The concept of the atom dates at the very least as far back as 440 B.C. Come Democritus, a Greek scientist and also philosopher. Democritus many likely built his theory of atom upon the occupational of previous philosophers, follow to Andrew G. Valve Melsen, writer of "From Atomos to Atom: The history of the principle Atom" (Duquesne college Press, 1952).

Democritus" explanation the the atom begins with a stone. A stone cut in fifty percent gives 2 halves the the very same stone. If the stone were come be repeatedly cut, at some suggest there would exist a item of the stone small enough that it can no longer be cut. The hatchet "atom" originates from the Greek word for indivisible, i beg your pardon Democritus concluded should be the allude at i beg your pardon a being (any type of matter) cannot be divided any more.

His explanation consisted of the ideas that atom exist independently from each other, that there are an boundless amount that atoms, that atoms space able come move, that they can integrate together to produce matter however do not merge to end up being a new atom, and that they cannot be divided, according to universe Today. However, due to the fact that most theorists at the moment — particularly the very influential Aristotle — thought that all matter was created from earth, air, fire and water, Democritus" atomic concept was placed aside.

John Dalton, a british chemist, built upon Democritus" principles in 1803 when he placed forth his own atomic theory, follow to the chemistry department at Purdue University. Dalton"s theory contained several concepts from Democritus, such as atoms space indivisible and also indestructible and that different atoms kind together to create all matter. Dalton"s enhancements to the theory included the following ideas: the all atom of a details element were identical, that atoms of one facet will have various weights and properties than atoms of one more element, that atoms cannot 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, showed that atoms have the right to be divided, according to the chemical Heritage Foundation. He to be able to identify the existence of electrons by examining the nature of electric discharge in cathode-ray tubes. According to Thomson"s 1897 paper, the rays to be deflected in ~ the tube, which verified that there to be something that was negatively charged in ~ the vacuum tube. In 1899, Thomson published a summary of his version of the atom, generally known together the "plum pudding model." one excerpt that this record is found on the Chem Team site. Thomson"s model of the atom contained a huge number of electron suspended in other that created a hopeful charge giving the atom an as whole neutral charge. His model resembled plum pudding, a popular British dessert that had actually raisins suspended in a ring cake-like ball.

The following scientist to more modify and advance the atomic model was Rutherford, that studied under Thomson, follow to the chemistry department at Purdue University. In 1911, Rutherford released his variation of the atom, which consisted of a positively charged nucleus orbited by electrons. This model arose when Rutherford and also his assistants fired alpha particles at slim sheets that gold. One alpha fragment is comprised of 2 protons and also two neutrons, all organized together through 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 to be scattered at very big angles come the initial direction of activity while the bulk passed ideal through fixed disturbed. Rutherford had the ability to approximate the size of the cell nucleus of the gold atom, finding it to be at least 10,000 times smaller sized than the dimension of the whole atom with lot of the atom being empty space. Rutherford"s version of the atom is still the an easy model that is offered today.

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

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This article was updated on Sept. 10, 2019, through Live science contributor Traci Pedersen.