Atoms consists a nucleus made of protons and neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms space the basic units of matter and also the specifying structure of elements. The ax "atom" originates from the Greek word for indivisible, since it was once thought the atoms to be the smallest things in the universe and also could no be divided. Us now recognize that atoms are comprised of 3 particles: protons, neutrons and also electrons — which room composed of even smaller particles, such together quarks.

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Atoms were produced after the big Bang 13.7 billion year ago. Together the hot, dense brand-new universe cooled, conditions became perfect for quarks and electrons come form. Quarks came with each other to type protons and also neutrons, and these particles an unified into nuclei. This all took location within the first few minutes of the universe"s existence, according to CERN.

It take it 380,000 years for the cosmos to cool sufficient to slow down the electron so that the nuclei could record them to type the an initial atoms. The earliest atoms were primarily hydrogen and helium, which room still the most abundant elements in the universe, according to Jefferson Lab. Gravity at some point caused clouds of gas to coalesce and type stars, and also heavier atoms to be (and tho are) developed within the stars and sent transparent the universe once the star exploded (supernova).

Atomic particles

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

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


The nucleus was discovered in 1911 by Ernest Rutherford, a physicist from brand-new Zealand. In 1920, Rutherford propose the name proton because that the positively charged particles that the atom. He also theorized the there was a neutral bit within the nucleus, i m sorry James Chadwick, a british physicist and student the Rutherford"s, was able to confirm in 1932.

Virtually all the massive of one atom resides in its nucleus, follow to Chemistry LibreTexts. The protons and neutrons that consist of the cell core are approximately the exact same mass (the proton is slightly less) and have the same angular momentum, or spin.

The nucleus is hosted together by the solid force, one of the four an easy forces in nature. This force between the protons and neutrons overcomes the repulsive electric force that would certainly otherwise press the protons apart, according to the rules of electricity. Some atomic nuclei room unstable because the binding force varies for different atoms based upon the size of the nucleus. This atoms will certainly then decay into other elements, such together carbon-14 decaying into nitrogen-14.


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


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

The variety of protons in one atom is unique to every element. Because that example, carbon atoms have actually six protons, hydrogen atoms have one and oxygen atoms have actually eight. The number of protons in one atom is described as the atomic variety of that element. The variety of protons also determines the chemical habits of the element. Aspects are arranged in the routine Table of the aspects in stimulate of raising atomic number.

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


Electrons room tiny compared to protons and neutrons, over 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 british physicist, uncovered the electron in 1897, according to the Science history Institute. Originally well-known as "corpuscles," electrons have actually a an unfavorable charge and are electrically attracted to the positively fee protons. Electrons surround the atom nucleus in pathways called orbitals, an idea that was placed forth by Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this design is well-known as the quantum version or the electron cloud model. The inside orbitals neighboring the atom are spherical yet the outer orbitals space much an ext complicated.

An atom"s electron configuration describes the locations of the electron in a usual atom. Making use of the electron configuration and also principles of physics, chemists have the right to predict one atom"s properties, such together stability, boiling suggest and conductivity, follow to the Los Alamos national Laboratory.


The neutron"s existence was theorized through Rutherford in 1920 and discovered through Chadwick in 1932, according to the American physics Society. Neutron were discovered during experiments once atoms were shot at a slim sheet that beryllium. Subatomic particles v no fee were exit – the neutron.

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

History the the atom

The concept of the atom days at least as far ago as 440 B.C. To Democritus, a Greek scientist and also philosopher. Democritus most likely constructed his theory of atom upon the work of previous philosophers, follow to Andrew G. Valve Melsen, author of "From Atomos come Atom: The history of the principle Atom" (Duquesne college Press, 1952).

Democritus" explanation that the atom starts with a stone. A rock cut in half gives two halves of the exact same stone. If the rock were come be repeatedly cut, at some allude there would certainly exist a piece of the stone tiny enough that it might no much longer be cut. The ax "atom" originates from the Greek word for indivisible, i beg your pardon Democritus concluded should be the allude at i m sorry a gift (any type of matter) cannot be divided any type of more.

His explanation included the concepts that atom exist separately from each other, the there are an infinite amount of atoms, the atoms space able come move, the they can integrate together to develop matter however do no merge to become a new atom, and that they can not be divided, according to cosmos Today. However, because most theorists at the time — particularly the very influential Aristotle — thought that all matter was created from earth, air, fire and also water, Democritus" atomic concept was placed aside.

John Dalton, a brother chemist, built upon Democritus" principles in 1803 when he placed forth his very own atomic theory, according to the chemistry room at Purdue University. Dalton"s theory contained several principles from Democritus, such as atoms are indivisible and indestructible and also that different atoms form together to produce all matter. Dalton"s enhancements to the theory had the adhering to ideas: that all atom of a particular element were identical, that atoms of one facet will have various weights and properties 보다 atoms of one more element, the atoms can not be produced or destroyed and that matter is formed by atom combining in basic whole numbers.

Thomson, the brothers physicist who found the electron in 1897, showed that atoms deserve to be divided, follow to the chemical Heritage Foundation. He was able to determine the visibility 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 was something that was negative charged in ~ the vacuum tube. In 1899, Thomson released a description of his version of the atom, generally known together the "plum pudding model." an excerpt the this paper is found on the Chem Team site. Thomson"s design of the atom consisted of a large number of electron suspended in something that created a optimistic charge providing the atom an in its entirety neutral charge. His design resembled plum pudding, a famous British dessert that had raisins suspended in a round cake-like ball.

The next scientist to further modify and advance the atomic design was Rutherford, that studied under Thomson, according to the chemistry room at Purdue University. In 1911, Rutherford released his version of the atom, which contained a positively charged nucleus orbited through electrons. This model occurred when Rutherford and his assistants fired alpha corpuscle at thin sheets of gold. An alpha particle is consisted of of 2 protons and also two neutrons, all organized together through the same strong nuclear pressure that binds the nucleus, according to the Jefferson Lab.

The scientists noticed the a little percentage of the alpha particles to be scattered at very huge angles come the original direction of activity while the bulk passed right through fixed disturbed. Rutherford had the ability to approximate the size of the cell core of the yellow atom, finding that to it is in at the very least 10,000 times smaller sized than the dimension of the entire atom with much of the atom being empty space. Rutherford"s version of the atom is quiet the straightforward model the is offered today.

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

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This write-up was update on Sept. 10, 2019, by Live scientific research contributor Traci Pedersen.