Ion
An ion is defined as an atom or molecule that carries an electric charge due to the loss or gain of electrons. When an atom loses electrons, it becomes a positively charged ion known as a cation, while gaining electrons results in a negatively charged ion called an anion. These charged particles play essential roles in various chemical processes, including the formation of ionic compounds, which occur when cations and anions bond together due to their opposing charges. A classic example is the interaction between sodium and chlorine, where sodium becomes a cation and chlorine an anion, resulting in the formation of table salt (sodium chloride).
The study of ions dates back to the 19th century, with significant contributions from scientists like Michael Faraday, who explored the conduction of electricity through solutions, and Svante Arrhenius, who clarified the dissociation of electrolytes into ions. Additionally, ions are vital in biological processes, such as cellular respiration, and they determine the acidity of solutions through the presence of hydronium ions, affecting cellular function and survival. Understanding the behavior of ions is fundamental in both chemistry and biology, highlighting their importance across various scientific fields.
On this Page
Ion
An ion is an atom or molecule that bears an electric charge. Certain atoms have a tendency either to lose or to gain electrons, thus developing either a positive or a negative charge. A positively charged ion is called a cation, while a negatively charged ion is an anion.
The formation of ions allows for the creation of compounds that are necessary for living organisms to survive. For example, hydrogen ions play a very important role in cellular respiration, the process by which organisms break down food into usable energy.
Brief History
Ions were first identified and named in 1834, by English chemist and physicist Michael Faraday (1791–1867). During the 1830s, Faraday spent a great deal of time experimenting with electric currents, specifically how dissolving certain substances in water would enable them to conduct electric current much more easily. He discovered that certain compounds, which he called electrolytes, would break down into their component parts when he ran an electric current through them. This process is known as electrolysis.
The nature of ions was not fully understood until 1884, when Swedish chemist and physicist Svante August Arrhenius (1859–1927) described the process in his doctoral thesis. Whereas Faraday had believed that ions were newly created during electrolysis, Arrhenius proposed that the individual ions were already present in electrolytes and that they would dissociate, or separate from one another, when diluted in an aqueous solution. Together, Faraday’s and Arrhenius’s work explained why ions behave the way they do.
Overview
An atom consists of three main subatomic particles: protons, electrons, and neutrons. Protons carry a positive charge, electrons carry a negative charge, and neutrons are electrically neutral, meaning they carry no charge. Because the magnitudes of the positive charge of each proton (+1) and the negative charge of each electron (−1) are equal, they cancel each other out; thus, any atom with an equal number of protons and electrons is neutral and has no charge. Ions are formed whenever an electrically neutral atom loses (donates) or gains (accepts) an electron, making the number of protons and electrons unequal and thereby changing the atom’s overall charge.
A common example of ion formation is the interaction between sodium (Na) and chlorine (Cl). Chlorine is the more electronegative of the two elements, meaning that it attracts electrons more strongly than sodium does. Because of this, when sodium and chlorine are combined, the chlorine atom will “steal” one of sodium’s electrons. As a result, the chlorine atom has one more electron than it does protons, making it a negatively charged anion with an overall charge of −1; conversely, the sodium atom has one fewer electron than it does protons, making it a positively charged cation with an overall charge of +1.
Naturally, a negatively charged anion and a positively charged cation are electrically attracted to one another. When this attraction holds two ions together to form a molecule, it is known as an ionic bond, and the resulting compound is called an ionic compound, or a salt. In the example above, the formation of the sodium and chlorine ions creates an ionic bond between the chlorine anion (Cl−) and the sodium cation (Na+) to produce the ionic compound sodium chloride (NaCl), which is simply household table salt.
Another example of an ionic compound is lithium chloride (LiCl), formed from chlorine and lithium. As in the previous example, chlorine will steal electrons from lithium, creating positive and negative ions in the process. These negatively and positively charged ions are then attracted to each other and come together to form lithium chloride. The electrical attraction between the positively charged lithium ions (Li+) and the negatively charged chlorine ions is not very strong, and they can easily be separated by adding water to them.
Whenever ions bond together to create ionic compounds, they also develop the ability to conduct electricity when dissolved in water. When salt is dissolved in water, for instance, the positive and negative ions dissociate and float around independently within the solution. This is because water is a polar compound, with a positively charged region at one end of the molecule and a negatively charged region at the other, and these regions of electrical charge pull apart the individual ions that make up an ionic compound. The presence of the free-floating ions in the solution makes it an excellent conductor for electricity.
Hydrogen ions, also known as hydronium, are what determine the acidity of an aqueous solution. The acidity of a substance is expressed in terms of its pH, a measurement derived from the notation p[H+], meaning the negative logarithm (p) of the molar concentration of hydronium ions in the solution. pH is measured on a scale of 0 (most acidic) to 14 (most basic). Pure water is considered to be a neutral solution because it has a pH of 7. In living organisms, the ability of cells to maintain the correct pH level is crucial for their survival; if a cell cannot regulate its hydronium ion concentration, it will not be able to function, and it will die as a result. Most cells thrive with pH levels of 7.0 to 7.4, although certain bacteria are able to survive in extremely acidic or basic environments.
In chemistry, there are two different definitions of acids and bases, both centered on the activity of hydronium ions. According to the Arrhenius definition, an acid is any substance that dissociates in water to form hydronium ions, while a base is any substance that dissociates in water to form hydroxide (OH−) ions. According to the Brønsted-Lowry definition, devised independently by Johannes Nicolaus Brønsted (1879–1947) and Martin Lowry (1874–1936), an acid is any compound that will donate hydronium ions, while a base is any compound that will accept hydronium ions. A hydronium ion is often also referred to as a proton because it in fact consists only of a single proton, with no neutron in the nucleus and no electron orbiting it; thus, accepting a hydronium ion is known as protonation, while donating one is known as deprotonation.
Bibliography
Atkins, Peter. Reactions: The Private Life of Atoms. New York: Oxford UP, 2011. Print.
Green, Dan. Chemistry: Getting a Big Reaction. Illus. Simon Basher. New York: Kingfisher, 2010. Print.
Gupta, Riti. "How to Calculate the Charge of an Ion." Sciencing, 1 Feb. 2020, sciencing.com/calculate-charge-ion-5955179.html. Accessed 28 Dec. 2022.
Klein, David R. Organic Chemistry. Hoboken: Wiley, 2012. Print.
Malone, Leo J., and Theodore O. Dolter. Basic Concepts of Chemistry. 9th ed. Hoboken: Wiley, 2013. Print.
McGrayne, Sharon Bertsch. Prometheans in the Lab: Chemistry and the Making of the Modern World. New York: McGraw, 2001. Print.
Myers, Richard L. The Basics of Chemistry. Westport: Greenwood, 2003. Print.
Thompson, Robert Bruce. Illustrated Guide to Home Chemistry Experiments: All Lab, No Lecture. Sebastopol: Maker Media, 2008. Print.
Tro, Nivaldo J. Chemistry: A Molecular Approach. 3rd ed. Upper Saddle River: Prentice, 2014. Print.