Atoms consist of a nucleus do of protons and neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms are the basic units of matter and the specifying structure of elements. The term "atom" originates from the Greek word because that indivisible, due to the fact that it was as soon as thought the atoms were the smallest points in the universe and also could no be divided. We now recognize that atoms are consisted of of three particles: protons, neutrons and also electrons — which room composed of also smaller particles, such as quarks.

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Atoms were developed after the big Bang 13.7 billion years ago. As the hot, dense brand-new universe cooled, conditions became an ideal for quarks and also electrons come form. Quarks came together to form protons and also neutrons, and these particles combined into nuclei. This every took ar within the first couple of minutes the the universe"s existence, according to CERN.

It take it 380,000 years because that the universe to cool enough to slow-moving down the electrons so that the nuclei could capture them to form the very first atoms. The earliest atom were primarily hydrogen and helium, which are still the many abundant aspects in the universe, follow to Jefferson Lab. Gravity ultimately caused clouds that gas come coalesce and kind stars, and heavier atoms were (and quiet are) created within the stars and sent transparent the universe when the star explosive (supernova).

Atomic particles

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

Protons and neutrons have roughly the exact same mass. However, one proton is around 1,835 times an ext massive than an electron. Atoms constantly have one equal number of protons and electrons, and the number of protons and also neutrons is usually the exact same as well. Including a proton come an atom provides a brand-new element, while including a neutron provides 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 name proton for the positively fee particles of the atom. He additionally theorized that there to be a neutral fragment within the nucleus, which James Chadwick, a british physicist and also student the Rutherford"s, had the ability to confirm in 1932.

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

The cell nucleus is organized together by the solid force, among the four straightforward forces in nature. This force in between the protons and neutrons overcomes the repulsive electrical force that would certainly otherwise press the proton apart, according to the rules of electricity. Some atomic nuclei are unstable because the binding force varies for various atoms based upon the dimension of the nucleus. This atoms will then degeneration into other elements, such together carbon-14 decaying into nitrogen-14.


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


Protons are positively fee particles uncovered within atom nuclei. Rutherford found them in experiments v cathode-ray tubes the were conducted between 1911 and also 1919. Proton are around 99.86% as massive as neutrons.

The number of protons in an atom is distinctive to each element. Because that example, carbon atoms have actually six protons, hydrogen atoms have one and oxygen atoms have eight. The variety of protons in an atom is described as the atomic number of that element. The number of protons also determines the chemical behavior of the element. Aspects are arranged in the regular Table of the elements in bespeak of boosting atomic number.

Three quarks comprise each proton — 2 "up" quarks (each v a two-thirds optimistic charge) and one "down" quark (with a one-third an adverse charge) — and they are held together by various other subatomic particles dubbed gluons, which room massless.


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

Joseph man (J.J.) Thomson, a brothers physicist, discovered the electron in 1897, follow to the Science history Institute. Originally well-known as "corpuscles," electrons have a an unfavorable charge and are electrically attractive to the positively fee protons. Electrons surround the atomic nucleus in pathways called orbitals, one idea that was put forth through Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this model is well-known as the quantum version or the electron cloud model. The inner orbitals bordering the atom space spherical however the outer orbitals space much more complicated.

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


The neutron"s presence was theorized through Rutherford in 1920 and discovered by Chadwick in 1932, according to the American physical Society. Neutron were found during experiments when atoms were shot in ~ a slim sheet that beryllium. Subatomic particles through no charge were released – the neutron.

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

History the the atom

The theory of the atom dates at least as far earlier as 440 B.C. Come Democritus, a Greek scientist and also philosopher. Democritus most likely developed his theory of atom upon the work-related of past philosophers, according to Andrew G. Van Melsen, author of "From Atomos to Atom: The background of the principle Atom" (Duquesne college Press, 1952).

Democritus" explanation that the atom starts with a stone. A rock cut in fifty percent gives 2 halves of the very same stone. If the rock were to be repeatedly cut, in ~ some suggest there would exist a piece of the stone little enough the it could no longer be cut. The hatchet "atom" comes from the Greek word because that indivisible, which Democritus concluded should be the point at i m sorry a gift (any kind of matter) cannot be divided any kind of more.

His explanation had the concepts that atom exist individually from every other, the there room an unlimited amount that atoms, that atoms are able to move, the they can integrate together to create matter but do no merge to end up being a new atom, and that they can not be divided, follow to world Today. However, due to the fact that most theorists at the time — especially the very influential Aristotle — believed that all matter was created from earth, air, fire and water, Democritus" atomic theory was put aside.

John Dalton, a brothers chemist, constructed upon Democritus" principles in 1803 as soon as 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 indestructible and also that different atoms kind together to produce all matter. Dalton"s additions to the theory included the adhering to ideas: that all atom of a specific element to be identical, that atoms of one facet will have different weights and also properties 보다 atoms of one more element, the atoms cannot be created or destroyed and that issue is created by atoms combining in straightforward whole numbers.

Thomson, the british physicist who discovered the electron in 1897, proved that atoms deserve to be divided, according to the chemistry Heritage Foundation. He to be able to determine the existence of electrons by researching the properties of electrical discharge in cathode-ray tubes. According to Thomson"s 1897 paper, the rays were deflected within the tube, which showed that there to be something that was negatively charged within the vacuum tube. In 1899, Thomson released a summary of his variation of the atom, commonly known together the "plum pudding model." one excerpt of this document is discovered on the Chem Team site. Thomson"s version of the atom consisted of a large number of electrons suspended in other that created a hopeful charge providing the atom an all at once neutral charge. His model resembled plum pudding, a popular British dessert that had actually raisins rely in a ring cake-like ball.

The following scientist to additional modify and breakthrough the atomic version was Rutherford, that studied under Thomson, according to the chemistry room at Purdue University. In 1911, Rutherford released his variation of the atom, which consisted of a positively charged nucleus orbited by electrons. This model occurred when Rutherford and his aides fired alpha corpuscle at slim sheets the gold. An alpha bit is consisted of of 2 protons and two neutrons, all organized together through the same strong nuclear pressure that binding the nucleus, according to the Jefferson Lab.

The scientists noticed that a little percentage the the alpha particles to be scattered at very huge angles to the initial direction of movement while the bulk passed ideal through fixed disturbed. Rutherford had the ability to approximate the dimension of the nucleus of the yellow atom, finding that to it is in at the very least 10,000 times smaller sized than the size of the whole atom with lot of the atom being empty space. Rutherford"s model of the atom is quiet the an easy model the is provided today.

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

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This article was to update on Sept. 10, 2019, through Live scientific research contributor Traci Pedersen.