Group 8 elements, also called noble gases, are known for not reacting with other elements. They have a full outer shell of electrons, which is the most stable electron configuration. However, other elements don't have this stable arrangement and must gain, lose, or share electrons. Ionic bonding is a way of achieving this stable configuration. This article will talk about ionic bonding in physical chemistry. We'll explain what ionic bonding is, show examples and diagrams of common ionic compounds, and explore giant ionic lattices and their properties. We'll also talk about the strength of ionic bonding and ionic radius. Finally, we'll review the evidence for ionic bonding. Understanding ionic bonding is important in understanding how atoms interact with each other. So, let's dive in and learn about it!

Ionic bonding definition

Atoms can achieve a noble gas structure in different ways. Non-metals can share their outer shell electrons by joining up in pairs, trios, or larger groups (see Covalent Bond). Groups of metal atoms of the same element will lose electrons to form positive ions in a sea of delocalized electrons (see Metallic Bonding). But when a metal and a non-metal come together, the easiest way for both to obtain a full outer shell is by transferring electrons. One species loses electrons, and the other gains them, forming ions. Oppositely charged ions bond ionically with each other by electrostatic attraction. That's what we call an ionic bond. Let's explore this process a little further. Understanding ionic bonding is important in understanding how atoms interact with each other. So, let's dive in and learn about it!

Ions

Ions are atoms that have gained or lost one or more electrons to form a charged particle. Ionic bonding always occurs between positively charged ions, called cations, and negatively charged ions, called anions. In both cases, the ions have the electron configuration of a noble gas. One element loses electrons. Because electrons are negative, this results in a cation.The other element gains these electrons. This results in an anion.Both ions end up with full outer shells of electrons.In ionic bonding, the cation is always a metal and the anion is always a non-metal. Overall, the charges on the ions cancel out, making a neutral compound.We call this  transfer of electrons electrovalence.

Electrostatic attraction

Forming ions is only half the picture - By definition, ionic bonding doesn’t involve the transfer of electrons at all! Rather, it is about the interaction between these ions as a result of gaining or losing electrons. When two oppositely charged species are close by, they attract each other. This is known as electrostatic attraction; you might also remember that this is the force that attracts electrons towards the nucleus in an atom. When mixed together, cations and anions are electrostatically attracted to one another, and ionic bonding is simply another term for this attraction.

Ionic bonding example and diagram

Now, let's consider an example of ionic bonding. Sodium chloride is a compound made up of positive sodium cations and negative chloride anions. We can determine the charges of these ions based on their electron configurations. Sodium has an electron configuration of 1s2 2s2 2p6 3s1. It can achieve a full outer shell by losing one electron from its 3s sub-shell, resulting in a configuration of 1s2 2s2 2p6. Since electrons are negatively charged, losing one results in a positive ion with a charge of +1. Chloride, on the other hand, has an electron configuration of 1s2 2s2 2p6 3s2 3p5. It can achieve a full outer shell by gaining one electron, resulting in a configuration of 1s2 2s2 2p6 3s2 3p6. Gaining an electron results in a negative ion with a charge of -1. The formula for sodium chloride is NaCl, with one sodium ion and one chloride ion. We can represent the ionic bonding using a dot and cross diagram:

This diagram shows the transfer of an electron from sodium to chlorine, resulting in the formation of Na+ and Cl- ions. The opposite charges of these ions attract each other, forming an ionic bond in the compound NaCl.

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Chlorine, however, has the structure 1s2 2s2 2p6 3s2 3p5. In order to have a full outer shell, it needs to gain one electron. In fact, it takes the electron that sodium loses. This forms a negative ion with the electron configuration 1s2 2s2 2p6 3s2 3p6:

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Each sodium atom loses one electron to form a positive sodium ion with a charge of 1+, whilst each chlorine atom accepts one electron to form a negative chloride ion with a charge of 1-. Therefore, the ions form a compound with a 1:1 ratio of sodium ions to chloride ions. This has the formula NaCl:

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Represent the ionic bonding in magnesium oxide using a dot and cross diagram. Include the charge of each ion and the formula of the compound. Magnesium has an electron configuration of 1s2 2s2 2p6 3s2. To achieve a full outer shell, each atom needs to lose two electrons from its 3s sub-shell. This forms a cation with a charge of 2+ and an electron configuration of 1s2 2s2 2p6. Oxygen, however, has the electron configuration 1s2 2s2 2p4. Each atom needs to gain two electrons to form an anion with a charge of 2- and an electron configuration of 1s2 2s2 2p6.  

Note that each magnesium atom loses two electrons, whilst each oxygen atom gains two electrons. The ratio of magnesium ions to oxygen ions is therefore 1:1, giving us the formula MgO. Here's the final dot and cross diagram:

Let's consider another example of ionic bonding with a compound that doesn't have a simple 1:1 ratio of cations to anions. Calcium fluoride is a compound made up of calcium cations and fluoride anions. We can determine the electron configurations of these ions to understand the process of ionic bonding. Calcium has an electron configuration of [Ar] 4s2. To achieve a full outer shell, each calcium atom needs to lose two electrons from its 4s sub-shell, resulting in a configuration of [Ar]. Fluorine has an electron configuration of [He] 2s2 2p5. Each fluorine atom needs to gain one electron to form a fluoride ion with a configuration of [Ne]. Note that while each calcium atom loses two electrons, each fluorine atom gains just one. Therefore, we need twice as many fluoride ions as calcium ions to balance the charges. This gives calcium fluoride the chemical formula CaF2, with one calcium ion and two fluoride ions. We can represent the ionic bonding using a dot and cross diagram:

This diagram shows the transfer of two electrons from each calcium atom to two fluoride atoms, resulting in the formation of Ca2+ and F- ions. The opposite charges of these ions attract each other, forming an ionic bond in the compound CaF2.

Giant ionic lattices

It's important to note that ionic compounds don't form discrete molecules like covalent compounds do. Instead, they form giant ionic lattices. In these lattices, each ion is surrounded by ions of opposite charge, forming a repeating pattern that extends in all directions. In the case of sodium chloride, as discussed earlier, the ratio of sodium ions to chloride ions is 1:1. The compound forms a repeating lattice in which each sodium ion is surrounded by six chloride ions, and each chloride ion is surrounded by six sodium ions. These ions are held together by strong electrostatic forces, forming a solid structure with high melting and boiling points. The lattice structure of sodium chloride can be represented as follows: This diagram shows a small section of the repeating lattice structure of sodium chloride, with sodium ions (Na+) represented by blue spheres and chloride ions (Cl-) represented by green spheres. Each ion is surrounded by ions of opposite charge, forming a three-dimensional network of alternating positive and negative ions.

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Note that the lattice stretches infinitely in all directions, and that each ion bonds to up to six oppositely charged ions.

Properties of ionic bonding

Ionic bonds are very strong. This means that they require a lot of energy to overcome. We also know that all ionically-bound species form giant ionic compounds, made up of oppositely charged ions held together by strong ionic bonds in all directions. This gives giant ionic compounds certain properties:

Giant ionic compounds have high melting and boiling points because the electrostatic attraction between ions is strong and requires a lot of energy to overcome. Because of this, they are generally solid at room temperature. The charged ions in giant ionic compounds can form bonds with polar water molecules. The energy released overcomes the ionic bonds holding the lattice together and dissolves the compound, meaning giant ionic compounds are soluble in water. When molten or in aqueous solution, ionic compounds can conduct electricity. This is because the ions are free to move and carry a charge. Giant ionic compounds are hard and strong due to the high strength of the electrostatic attraction between oppositely charged ions. Ionic compounds are fairly brittle. If you give them a sharp blow, you may distort the carefully positioned lattice structure. This results in two ions with the same charge adjacent to each other. These ions would repel each other and shatter the compound.

Strength of ionic bonding

The trend in ionic radius for the series of isoelectronic ions from N3- to Al3+ is that the ionic radius decreases as the positive charge of the ion increases. This is because, as the number of protons in the nucleus increases, there is a stronger attraction between the positive charge in the nucleus and the negatively charged electrons in the ion. This pulls the electrons closer to the nucleus, resulting in a smaller ionic radius. In contrast, as the negative charge of the ion increases, there are more electrons in the ion, which creates more electron-electron repulsion. This causes the electrons to spread out further from the nucleus, resulting in a larger ionic radius. Therefore, N3- has the largest ionic radius and Al3+ has the smallest ionic radius in this series of isoelectronic ions.

Evidence for ionic bonding

In conclusion, ionic bonding is a fundamental type of chemical bonding that occurs between metal cations and non-metal anions. This electrostatic attraction between oppositely charged ions results in the formation of ionic compounds, which have unique properties such as giant ionic lattices, high melting/boiling points, and solubility in water. The strength of ionic bonding depends on the charge and size of the ion, and the ionic radius can vary depending on the number of electron shells and the charge of the ion. The existence of ions and the evidence for ionic bonding is supported by electrolysis experiments. Understanding ionic bonding is essential for understanding the properties and behaviors of many important compounds and materials.

Ionic Bonding

What is an ionic bond?

An ionic bond is the electrostatic attraction between oppositely charged ions.

How are ionic bonds formed?

Ionic bonds are formed when a metal donates electrons to a non-metal, forming charged ions, which are then attracted to each other.

What happens to electrons in an ionic bond?

An ionic bond does not involve electrons. Rather, the bond is the electrostatic attraction between charged ions. These ions are formed through the movement of electrons.

What is the difference between ionic and covalent bonds?

A covalent bond is a shared pair of electrons, whilst an ionic bond is the electrostatic attraction between oppositely charged ions.

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