Atoms consists a nucleus make of protons and neutrons orbited through electrons. (Image credit: Shutterstock)
Atoms room the an easy units the matter and the defining structure of elements. The term "atom" comes from the Greek word because that indivisible, because it was when thought that atoms were the smallest points in the universe and could not be divided. We now know that atom are comprised of three particles: protons, neutrons and also electrons — which room composed of also smaller particles, such together quarks.

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

It take it 380,000 years for the cosmos to cool enough to sluggish down the electrons so the the nuclei could record them to form the very first atoms. The earliest atom were generally hydrogen and also helium, which are still the most abundant aspects in the universe, according to Jefferson Lab. Gravity at some point caused clouds the gas come coalesce and type stars, and heavier atoms to be (and quiet are) produced within the stars and also sent transparent the universe once the star exploded (supernova).

Atomic particles

Protons and also neutrons room heavier 보다 electrons and also reside in the nucleus in ~ the facility of the atom. Electron are incredibly lightweight and also 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 national Laboratory.

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


The cell nucleus was uncovered in 1911 by Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford propose the surname proton because that the positively fee particles that the atom. He likewise theorized that there to be a neutral fragment within the nucleus, i m sorry James Chadwick, a brother physicist and student that Rutherford"s, was able to confirm in 1932.

Virtually every the fixed of one atom resides in its nucleus, follow to Chemistry LibreTexts. The protons and neutrons that consist of the cell core are roughly the same mass (the proton is contempt less) and also have the same angular momentum, or spin.

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


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


Protons space positively charged particles discovered within atomic nuclei. Rutherford found them in experiments v cathode-ray tubes that were conducted in between 1911 and 1919. Protons are about 99.86% as huge as neutrons.

The variety of protons in an atom is unique to every element. For example, carbon atoms have six protons, hydrogen atoms have actually one and oxygen atoms have actually eight. The number of protons in one atom is described as the atomic variety of that element. The number of protons also determines the chemical behavior of the element. Facets are i ordered it in the regular Table of the aspects in stimulate of boosting atomic number.

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


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

Joseph john (J.J.) Thomson, a british physicist, uncovered the electron in 1897, follow to the Science history Institute. Originally well-known as "corpuscles," electrons have actually a an unfavorable charge and are electrically attractive to the positively charged protons. Electron surround the atomic nucleus in pathways referred to as orbitals, one idea the was placed forth through Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this version is well-known as the quantum design or the electron cloud model. The inside orbitals surrounding the atom room spherical yet the external orbitals room much more complicated.

An atom"s electron configuration describes the locations of the electrons in a typical atom. Using the electron configuration and also principles of physics, chemists can predict an atom"s properties, such as stability, boiling suggest and conductivity, according to the Los Alamos national Laboratory.


The neutron"s existence was theorized by Rutherford in 1920 and discovered by Chadwick in 1932, follow to the American physical Society. Neutrons were discovered during experiments when atoms to be shot in ~ a thin sheet that beryllium. Subatomic particles v no fee were exit – the neutron.

Neutrons space uncharged particles uncovered within every atomic nuclei (except for hydrogen). A neutron"s mass is slightly larger than the of a proton. Like protons, neutrons are also made the quarks — one "up" quark (with a optimistic 2/3 charge) and two "down" quarks (each v a an unfavorable 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 also philosopher. Democritus many likely constructed his theory of atoms upon the job-related of previous philosophers, according to Andrew G. Van Melsen, writer of "From Atomos to Atom: The history of the concept Atom" (Duquesne college Press, 1952).

Democritus" explanation of the atom starts with a stone. A stone cut in half gives two halves that the exact same stone. If the stone were come be repetitively cut, at some allude there would certainly exist a item of the stone little enough the it can no much longer be cut. The ax "atom" originates from the Greek word for indivisible, i m sorry Democritus concluded have to be the point at which a being (any kind of matter) cannot be divided any kind of more.

His explanation included the principles that atom exist separately from each other, that there space an boundless amount of atoms, the atoms room able to move, the they can combine together to develop matter however do not merge to come to be a brand-new atom, and that they can not be divided, follow to universe Today. However, since most thinkers at the time — specifically the an extremely influential Aristotle — believed that all issue was created from earth, air, fire and water, Democritus" atomic theory was put aside.

John Dalton, a british chemist, built upon Democritus" ideas in 1803 when he put forth his own atomic theory, follow to the chemistry department at Purdue University. Dalton"s theory consisted of several concepts from Democritus, such as atoms space indivisible and also indestructible and also that various atoms type together to produce all matter. Dalton"s additions to the theory contained the complying with ideas: the all atom of a specific element to be identical, the atoms the one aspect will have various weights and properties than atoms of another element, that atoms cannot be produced or destroyed and that issue is developed by atoms combining in simple whole numbers.

Thomson, the british physicist who uncovered the electron in 1897, confirmed that atoms have the right to be divided, follow to the chemical Heritage Foundation. He to be able to identify the presence of electrons by researching the nature of electrical discharge in cathode-ray tubes. According to Thomson"s 1897 paper, the rays were deflected within the tube, which proved that there was something the was negative charged within the vacuum tube. In 1899, Thomson released a summary of his variation of the atom, typically known as the "plum pudding model." an excerpt of this paper is discovered on the Chem Team site. Thomson"s design of the atom contained a large number of electrons suspended in other that created a hopeful charge providing the atom an as whole neutral charge. His version resembled plum pudding, a well-known British dessert that had raisins suspended in a ring cake-like ball.

The next scientist to additional modify and advancement the atomic design 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 developed when Rutherford and also his aides fired alpha particles at slim sheets of gold. One alpha fragment is comprised of 2 protons and also two neutrons, all hosted together by the same strong nuclear force that binding the nucleus, according to the Jefferson Lab.

The researchers noticed the a little percentage that the alpha particles were scattered in ~ very big angles to the original direction of motion while the bulk passed appropriate through hardly disturbed. Rutherford was able to approximate the size of the nucleus of the yellow atom, finding that to be at least 10,000 times smaller than the dimension of the whole atom with lot of the atom being empty space. Rutherford"s version of the atom is tho the straightforward model that is supplied today.

Several various other scientists enhanced the atomic model, including Niels Bohr (built top top Rutherford"s design to include properties the electrons based upon the hydrogen spectrum), Erwin Schrödinger (developed the quantum design 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 occurred the theory that protons and neutrons were composed of quarks).

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