Difference Between Atom and Ion (With Table)

A chemical element comprises several units which have their independent properties, functions and chemistry with different units of their types or another. It is because of these small segments that an element has its unique roles, aspects and usages. Two of them are- 1. Atom 2. Ion.

Atom vs Ion

The main difference between an atom and an ion is that the atom is electrically neutral, and an ion is electrically charged. The reason behind an atom’s neutral electrical charge is the presence of an equal number of protons and electrons. On the other hand, an ion has an independent positive or negative charge.

The smallest content of a chemical element is called an atom that constitutes protons, electrons and neutrons. Almost all the mass of an atom is responsible because of the nucleus. Particles with a positive charge present in an atom are called protons, particles with a negative charge are called electrons and those with no charge are called neutrons.

An ion is that part of a chemical element that has a net electric charge. An ion doesn’t have an equal number of electrons and protons, which is why it possesses a net electric charge. An ion is of two types- (1) cation (2) anion. An ion with a positive charge which contains limited electrons is called a cation. An ion with a negative charge which contains surplus electrons is called an anion. Both cations and anions are oppositely charged, and hence they attract each other, and their resultant product is an ionic compound.

Comparison Table Between Atom and Ion

Parameters Of ComparisonAtomIon
DefinitionThe smallest content of a chemical element is known as an atom.A charged subatomic particle of a chemical element is known as an ion.
First discovered in450 B.C.1834
First discovered byDemocritusMichael Faraday
TerminologyDerived from an ancient Greek word “atomos” Derived from an ancient Greek word “ἰόν”
ExamplesNeon, Hydrogen, Oxygen, Argon, Iron, Calcium, Fluorine, Chlorine, Sodium, Plutonium, Deuterium, Carbon, Sulphur, Bromine, Iodine, Potassium, Copper, Boron, Lithium, Cobalt, Nickelmonoatomic ions- F, Cl, Br, I, Li+
Polyatomic ions- SO42–, CO32−
Ionic compounds- sodium chloride, potassium chloride
Bibliographical references “From atomos to atom: the history of the concept of atom” by Andrew G. van Melsen, “Ernest Rutherford and the explosion of atoms” by John L. Heilbron, “A history of the electron” by Jaume Navarro“Earth” 14th edition by Frank Press and Raymond Siever, “Radiation Detection and Measurement” by Glenn Knoll

What is Atom?

The smallest content of a chemical element or the smallest particle of matter, in general, is called an atom. The main contents of an atom are proton, neutron and electrons. Protons have a positive charge. Electrons have a negative charge. Neutrons have no charge. Examples of an atom are Hydrogen, Oxygen, Scandium, Lead, Copper, Mercury, Sodium, Uranium, Krypton, Xenon, Barium, Sulphur.

There are several theories and postulates stated by several scientists regarding the physical and chemical properties, nature, behaviour and other parameters of an atom. John Dalton, an English chemist, discovered and stated the currently known “law of multiple proportions” theory wherein he inferred that several chemical elements consist of different ratios of mass and due to which their quantity altogether in a chemical compound is different from one another.

It was because of Sir J.J. Thomson that the world got familiar with the fact that an atom has other contents as well, namely, the nucleus. His discovery of the nucleus was based on a “plum pudding model”, which made it certain that an atom consists of a nucleus along with electrons, protons and neurons. Although, Ernest Rutherford, with his epiphanies regarding an atom, overcame the difficulties that were found in Thomson’s atomic model.

The history of an atom and various discoveries regarding it were initiated long back in Greek and Indian ancient cultures, and it is after that, that various discoveries about it such as the law of multiple proportions, Kinetic theory of gases, Brownian motion, Discovery of the nucleus, neutron, isotopes and electron, was possible. At present, the entire world is familiar with all sorts of information regarding an atom because of these remarkable and improved theories.

An atom had several properties with parameters such as nuclear properties, mass, shape and size, magnetic moment, energy levels, valence and bonding behaviours with other atoms, states etc. According to the Modern Periodic Table, Hydrogen is an element that has the least number of atoms in it.

What is Ion?

A charged subatomic particle of a chemical element is known as an ion. There are several subcategories of an ion. Based on their charge, the two main types of ion are- cations and anions. Cations have a positive charge. On the other hand, anions have a negative charge.

Furthermore, it is categorized based on the number of atoms present in it. Ions with a single atom are called monoatomic ions. On the contrary, polyatomic ions are ions that have two or more atoms. Both polyatomic and monoatomic ions can either be cations or anions. Since they are oppositely charged, they attract each other and form an ionic bond, and the resultant product is an ionic compound. Examples of monoatomic ions are F−, Cl−, Br−, I−, Li+, Na+, Rb+. Examples of polyatomic ions are SO42–, CO32−, CrO42-, PO43-, BO33-. Examples of ionic compounds are Pottasium chloride, Sodium chloride, Calcium oxide, Magnesium sulphide, Sodium phosphide, Lithium acetate, Silver bromide, Silver nitrate.

Michael Faraday and his correspondence William Whewell made the first discovery regarding an ion in the year 1834. Faraday did not know the nature of an ion back then, but he did believe that an ion requires an aqueous medium to travel from one electrode to the other. Whewell was the one to coin the terms cathode, anode, cations and anions.

Another key person in the history of ion is Svante Arrhenius. Arrhenius, in his hypothesis, in 1884, stated the justification of dissociation of solid crystalline salts into paired charged particles. He also believed that ions are formed despite the absence of electric current.

There are several properties of ions such as common ion effect, degree of ionization, ionization, ionization potential, ionic bond, inorganic ions, ionic transfer, electrode ionization, quinonoid zwitterion, tunnel ionization etc. Ions have several dailies as well as industrial applications such as an indication of water quality, air purification, they are used in smoke detectors etc.

Main Differences Between Atom and Ion

  1. Atom is electrically neutral. On the other hand, an ion has either a positive or a negative charge.
  2. Ions have more applications, whereas atoms have lesser applications.
  3. Ions have more properties than atoms.
  4. The mass of an atom can be calculated. On the other hand mass of an ion cannot be calculated, but a mass of an ionic compound can be calculated.
  5. The formula used for calculating an ionic compound’s mass is the sum of atomic masses of the ions present in the formula, whereas the formula used to calculate atomic mass is the sum of atoms present in the molecule.


Atoms and ions both are important parts of the compounds and elements that we witness today around us. Right from their varying history and their expanded branches of study in various subjects like chemistry, physics, nuclear science, rocket science, and others, various inventions and discoveries have taken place because of their effectiveness in a chemical element/ compound, which has been a great help to mankind.

In the Chernobyl nuclear power plant explosion in Ukraine, the authorities slowed down the radiation contamination spread by dumping boron, sand and clay in huge quantities on the areas of exploded reactor. It was ionic and atomic science that was used to save millions and trillions of lives in the Soviet Union.

Various branches of science have grown and evolved into their respective advanced forms because of the basic data present regarding the ions and atoms. Various applications and milestones have been achieved in the world of science because of the foundations of ions and atoms.


  1. https://books.google.com/books?hl=en&lr=&id=Yy0LAAAAIAAJ&oi=fnd&pg=PR5&dq=history+of+atoms&ots=0mattvVEVk&sig=xYchnIcl8MoSkKQ26xFgZKXgpAo
  2. https://books.google.com/books?hl=en&lr=&id=5JnzCAAAQBAJ&oi=fnd&pg=PA1&dq=atoms+ions&ots=WypZZNdo2D&sig=N2fZHMxHYgpcQtNsROVFZ80AG_s
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