Difference Between Anion and Cation

The key difference between anion and cation is that anions are the negatively charged ions formed from neutral atoms whereas cations are positively charged ions formed from neutral atoms.

Commonly, anions and cations are called ions. The atoms of various elements are not stable (except the noble gases) under normal conditions. To become stable, they undergo various chemical changes especially regarding the number of electrons. For example, they can remove or gain electrons or else share electrons to gain the stable electron configuration. When this is happening, elements tend to join with other elements. Chemical elements can join with each other to form chemical compounds. The elements bind to each other via chemical bonds that have ionic or covalent characteristics. If the compounds have ionic bonds, they are known as ionic compounds. Ionic compounds form by the attraction between positive and negative ions.

CONTENTS

1. Overview and Key Difference
2. What is Anion
3. What is Cation
4. Side by Side Comparison – Anion vs Cation in Tabular Form
5. Summary

What is Anion?

Anions are the negatively charged ions that form from neutral atoms. When an atom attracts one or more electrons to its outer orbital, negative ions form. In a neutral atom, the number of electrons in the outer shells is equal to the number of protons in the nucleus. Electrons are negatively charged subatomic particles, and protons are positively charged subatomic particles. Since the numbers are equal, the atoms have no net charge.

However, when an atom attracts more electrons from outside, the number of electrons increases, thus the atom becomes negatively charged. In order to attract electrons, there should be some other species, which readily gives electrons to anionic atoms. According to the number of electrons gained, the charge size varies. For example, if an atom obtains one electron, a monovalent anion forms and if it obtains two electrons in a divalent anions form.

Normally, anions form by non-metals elements, which are in the p block of the periodic table. For example, nitrogen forms a -3 anion; oxygen forms a -2 anion and chlorine forms a -1 anion. These atoms are more electronegative, hence can attract electrons and form anions. Not only single atoms, but there can be several atoms or molecules forming this type of ions. In addition, if the anion is only an atom, it is known as a monoatomic anion. If the anion has several atoms, or if it is a molecule, it is known as a polyatomic anion. Moreover, these ions attract to the positively charged electric fields or any positively charged species.

What is Cation?

Cations are positively charged ions. These ion form when a neutral atom removes one or more electrons. When they remove electrons, the number of protons in the nuclei is higher than the number of electrons in outer shells; hence, the atom gets a positive charge.

Cations form from metals in s block, transition metals, lanthanides and actinides, etc. Like the anions, cations can also have various charge sizes depending on the number of electrons removed. Therefore, they form monovalent (Na⁺), divalent (Ca²⁺), and trivalent (Al³⁺) cations. In addition, there can be monoatomic or polyatomic cations (NH₄⁺).

What is the Difference Between Anion and Cation?

Summary – Anion vs Cation

Anions and cations are forms of charged chemical species. The difference between anion and cation is that anions are the negatively charged ions formed from neutral atoms whereas cations are positively charged ions formed from neutral atoms.

Reference:

1. Helmenstine, Todd. “The Difference Between a Cation and an Anion.” ThoughtCo, Feb. 1, 2018. Available here 
2. “Ion.” Wikipedia, Wikimedia Foundation, 14 May 2018. Available here 

Image Courtesy:

1.’Ions’By Jkwchui – Own work, (CC BY-SA 3.0) via Commons Wikimedia