[Chemistry Class Notes] Ion Definition Pdf for Exam

What is an Ion?

An ion can be described as a chemical species that hold either a positive or negative charge of some amount of magnitude. The word ‘ion’ can be used to refer to molecules or atoms that hold non-zero net charges associated with them. Thus, all the ions contain either a greater number of protons compared to electrons in their overall molecular or atomic structure, or they have a greater electron count than the protons in their molecular/atomic structures. Ions that contain a greater proton count than the electrons are known to contain a net positive charge. Commonly, these ions are referred to as cations. On the other side, ions that hold a greater electron count than protons are known to contain a net negative charge. Commonly, these ions are referred to as anions.

Importance of Ion

It is important to make a note that the electrostatic forces of attraction which arise between the positively charged cations and negatively charged anions are described as the driving force behind the ionic bond formation. When the 2 oppositely charged ions produce an ionic bond with each other, the resulting compound type is commonly known as an ionic compound.

Whereas, if an ion is made of only 1 type of atom (each holding some amount of net charge, either positive or negative), it is referred to as either a monoatomic ion or an atomic ion. On the other side, if an ion is made of either 2 or more atoms, it is referred to as a molecular ion or a polyatomic ion.

Creation of Ions

There exist several methods for the preparation of ions. As an example, spontaneous collisions between the molecules of either a gaseous or liquid fluid can result in 1 of the electrons being knocked off a molecule/atom. This results in the production of a free electron and a positively charged ion. Commonly, this ionization type is known as physical ionization. The free-electron can even go on by attaching itself to another molecule or atom, resulting in creating a new anion, which is negatively charged.

The other important process via which ions can be formed is done by using chemical interactions. As an example, when an ionic compound like salt is dissolved in a suitable solvent (like water), the atoms that constitute that salt undergoes dissociation and produce free ions. However, when common salt, which is also called sodium chloride, is dissolved in water, it undergoes dissociation to generate chloride anions and sodium cations. It should also be noted that the symbol Cl denotes the chloride anions– and sodium cations are denoted using the symbol Na+.

Another important notable process via which ions can be formed is the passage of direct currents via some conducting solutions, which results in the production of ions in the solution. It is also be noted that the dissolving anodes through the ionization process yield huge amounts of free ions.

Representing the Charge on an Ion

To represent an ion and representing the charge on an ion (same ion), first, the ion’s chemical formula must be written. After that, the type of charge symbol held by the ion (‘+’ indicates positive charges, and ‘-‘ indicates negative charges) must be written in superscript, followed by the ion’s charge magnitude (including in superscript). It is essential to note that the sign is written after the charge magnitude for anions that hold the charges whose magnitudes fell greater than -1. It is also important to be noted that the charge magnitude is omitted if its value falls equal to 1. Thus, the sodium cation, whose charge is given as +1, can be represented as Na+.

Solved Examples on Ion Notation

Carbonate Anion

Carbonate anion’s chemical formula is given as CO3, and the magnitude of the negative charge held by it is given as 2. Thus, the effective charge held by the ion is given by -2. Therefore, the carbonate ion can be represented using the symbol CO32-

Zinc Cation

The chemical symbol of zinc is given as Zn and the positive charge carried by the zinc cation holds a magnitude of 2. Thus, the zinc cation is denoted using the symbol Zn2+.

Examples of Ions

Examples of Simple Cations – Monoatomic Cations

A few common examples of monoatomic cations are listed below.

• Calcium cation, which is denoted by the chemical formula Ca2+.

• Aluminium cation, which is denoted by the chemical formula Al3+.

Examples of Simple Anions – Monoatomic Anions

A few common examples of monoatomic anions are listed below.

• Sulfide anion, which is denoted using the chemical formula S2–.

• Fluoride anion, which is denoted using the chemical formula F–.

Examples of Polyatomic Anions – Molecular Anions

A few common examples of polyatomic anions are listed below.

• Hydroxide anion, which is denoted using the chemical formula OH–.

• Nitrate anion, which is denoted using the chemical formula NO3–.

• Sulfate anion, which is denoted using the chemical formula SO42-.