Atoms consist of a nucleus do of protons and also neutrons orbited by electrons. (Image credit: Shutterstock)
Atoms room the basic units that matter and the specifying structure of elements. The hatchet "atom" originates from the Greek word for indivisible, because it was when thought the atoms to be the smallest points in the universe and also could not be divided. Us now recognize that atoms are comprised of 3 particles: protons, neutrons and also electrons — which are composed of even smaller particles, such as quarks.

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Atoms were produced after the huge Bang 13.7 billion year ago. Together the hot, dense new universe cooled, conditions became perfect for quarks and electrons come form. Quarks came with each other to type protons and neutrons, and these particles linked into nuclei. This every took location within the first couple of minutes the the universe"s existence, follow to CERN.

It take it 380,000 years for the universe to cool enough to slow-moving down the electrons so that the nuclei could catch them to kind the first atoms. The earliest atom were primarily hydrogen and also helium, which room still the many abundant elements in the universe, follow to Jefferson Lab. Gravity at some point caused clouds the gas to coalesce and form stars, and also heavier atoms were (and quiet are) created within the stars and sent transparent the universe as soon as the star exploded (supernova).

Atomic particles

Protons and neutrons room heavier than electrons and reside in the nucleus at the center of the atom. Electrons are exceptionally lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times better than the nucleus, follow to the Los Alamos nationwide Laboratory.

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


The cell core was discovered in 1911 by Ernest Rutherford, a physicist from new Zealand. In 1920, Rutherford proposed the name proton for the positively fee particles that the atom. He additionally theorized that there to be a neutral fragment within the nucleus, i m sorry James Chadwick, a brother physicist and also student of Rutherford"s, was able to confirm in 1932.

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

The cell nucleus is held together by the strong force, one of the four basic forces in nature. This force 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 room unstable because the binding pressure varies for various atoms based upon the size of the nucleus. These atoms will then decay into various other elements, such as carbon-14 decaying right into nitrogen-14.


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


Protons room positively charged particles discovered within atom nuclei. Rutherford discovered them in experiments v cathode-ray tubes that were conducted between 1911 and also 1919. Proton are about 99.86% as substantial as neutrons.

The variety of protons in an atom is unique to each element. For example, carbon atoms have six protons, hydrogen atoms have one and oxygen atoms have actually eight. The variety of protons in an atom is referred to as the atomic variety of that element. The variety of protons additionally determines the chemical habits of the element. Aspects are i ordered it in the routine Table that the elements in bespeak of boosting atomic number.

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


Electrons space tiny compared to protons and also neutrons, over 1,800 times smaller than either a proton or a neutron. Electrons are around 0.054% as huge as neutrons, follow to Jefferson Lab.

Joseph man (J.J.) Thomson, a brother physicist, found the electron in 1897, follow to the Science history Institute. Originally well-known as "corpuscles," electrons have a negative charge and also are electrically attractive to the positively charged protons. Electrons surround the atomic nucleus in pathways dubbed orbitals, one idea the was placed forth by Erwin Schrödinger, one Austrian physicist, in the 1920s. Today, this design is recognized as the quantum model or the electron cloud model. The inner orbitals surrounding the atom are spherical yet the outer orbitals are much more complicated.

An atom"s electron configuration describes the areas of the electrons in a typical atom. Utilizing the electron configuration and principles that physics, chemists deserve to predict one atom"s properties, such as stability, boiling point and conductivity, according to the Los Alamos national Laboratory.


The neutron"s existence was theorized through Rutherford in 1920 and discovered by Chadwick in 1932, follow to the American physical Society. Neutron were uncovered during experiments as soon as atoms to be shot in ~ a slim sheet of beryllium. Subatomic particles through no charge were released – the neutron.

Neutrons are uncharged particles discovered within all atomic nuclei (except for hydrogen). A neutron"s mass is slightly bigger than that of a proton. Choose protons, neutrons are additionally made that quarks — one "up" quark (with a optimistic 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 back as 440 B.C. Come Democritus, a Greek scientist and philosopher. Democritus many likely developed his theory of atom upon the job-related of past philosophers, according to Andrew G. Valve Melsen, author of "From Atomos to Atom: The history of the ide Atom" (Duquesne college Press, 1952).

Democritus" explanation the the atom starts with a stone. A stone cut in fifty percent gives 2 halves that the exact same stone. If the rock were to be consistently cut, in ~ some suggest there would exist a item of the stone little enough that it might no longer be cut. The ax "atom" originates from the Greek word for indivisible, i m sorry Democritus concluded need to be the suggest at i beg your pardon a being (any form of matter) cannot be divided any type of more.

His explanation consisted of the concepts that atoms exist independently from each other, the there are an infinite amount the atoms, the atoms space able to move, the they can combine together to develop matter yet do not merge to become a new atom, and also that they cannot be divided, according to universe Today. However, since most theorists at the moment — especially the very influential Aristotle — believed that all matter was developed from earth, air, fire and water, Democritus" atomic theory was placed aside.

John Dalton, a brothers chemist, built upon Democritus" concepts in 1803 as soon as he put forth his very own atomic theory, according to the chemistry department at Purdue University. Dalton"s theory included several concepts from Democritus, such as atoms space indivisible and also indestructible and also that different atoms type together to produce all matter. Dalton"s additions to the theory consisted of the adhering to ideas: the all atom of a particular element to be identical, that atoms of one element will have different weights and properties 보다 atoms of one more element, the atoms cannot be produced or destroyed and also that matter is formed by atom combining in straightforward whole numbers.

Thomson, the brother physicist who discovered the electron in 1897, proved that atoms have the right to be divided, according to the chemistry Heritage Foundation. He to be able to identify 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 confirmed that there was something the was negative charged within the vacuum tube. In 1899, Thomson released a description of his version of the atom, commonly known as the "plum pudding model." one excerpt the this file is discovered on the Chem Team site. Thomson"s version of the atom consisted of a big number of electrons suspended in something that produced a optimistic charge giving the atom an as whole neutral charge. His version resembled plum pudding, a well-known British dessert that had actually raisins exposed in a round cake-like ball.

The next scientist to further modify and advance the atomic model was Rutherford, who studied under Thomson, follow to the chemistry department at Purdue University. In 1911, Rutherford published his variation of the atom, which had a positively fee nucleus orbited by electrons. This model emerged when Rutherford and also his assistants fired alpha particles at thin sheets of gold. An alpha particle is made up of two protons and also two neutrons, all organized together by the same strong nuclear force that binding the nucleus, according to the Jefferson Lab.

The scientists noticed that a small percentage of the alpha particles were scattered in ~ very large angles to the original direction of movement while the majority passed best 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 lot of the atom being empty space. Rutherford"s design of the atom is still the straightforward model the is used today.

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

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This write-up was updated on Sept. 10, 2019, through Live science contributor Traci Pedersen.