Molecular Structure, Bonding, and Polarity of MgO Lewis Structure

Magnesium Oxide (MgO) is found in rocks such as dolomite, silicate, and magnesite and is one of the most prevalent elements on Earth. Magnesium oxide, which is formed mostly by the calcination of magnesite, is also present in seawater (MgCO3).

Aside from that, there are other health benefits of consuming magnesium oxide, making it one of the most sought-after chemicals for scientific research.

Magnesium Oxide is hygroscopic, which means it has the ability to absorb or adsorb water molecules from the surrounding environment.

As a result, magnesium oxide in the human body reacts with water to form magnesium hydroxide, a well-known antacid that reduces acidity.

MgO + H2O → Mg(OH)2

Furthermore, magnesium oxide improves water retention in the human body, ensuring appropriate peristalsis activity.

Peristalsis is the involuntary movement of the muscles of the digestive tract that causes wavelike contractions. These contractions start a series of lengthy reflexes in the body that are linked to the stomach.

Magnesium Oxide (MgO) is a white substance that can cause inhalation problems when burned. In addition, magnesium oxide (MgO) is employed in the wastewater treatment, air emission treatment, drinking water treatment, and waste treatment industries for soil and water remediation.

What are valence electrons and what do they do?

Valence electrons are electrons that are found in the atom’s outermost shells. Because they are the furthest from the nucleus and carry the least degree of attraction from it, only these electrons engage in bond formation.

Because of this, even if there is only a slight attraction from another neighbouring atom, these electrons are activated and undergo bond formation, resulting in the synthesis of a new molecule.

Lewis Structure of MgO

The Lewis Structures aid in establishing how an atom’s valence electrons contribute in the bond creation that leads to the production of a molecule and, finally, a compound. It is investigated by looking at how the electrons in the outermost shell (valence electrons) interact to create single, double, and triple bonds.

Furthermore, the structure aids in determining the rationale for a molecule’s molecular geometry. As a result, Lewis diagrams are made more frequently for covalent compounds and less frequently for ionic compounds.

Magnesium oxide is an ionic molecule in which the valence electrons of magnesium are lost and the valence electrons of oxygen are received to form a stable state. This behaviour can be described by looking at the Lewis structure of magnesium oxide, which starts with looking at the atomic numbers of the chemical elements involved, which in this case are Magnesium and Oxygen.

Magnesium has an atomic number of 12 and an electronic structure of 1s2 2s2 2p6 3s2. The atomic number of oxygen, on the other hand, is 8, and its electronic configuration is 1s2 2s2 2p4.

Magnesium contains two valence electrons, whereas oxygen has six valence electrons, as can be seen from both electrical structures. It’s critical to remember that when a small number of valence electrons are present and many are needed to sustain the shell, electrons from the outermost shell are contributed.

The valence electrons, on the other hand, are accepted when there are plenty of them already present, and admitting only a handful would enough for the octet. Because oxygen already has six valence electrons and only needs two to stabilise its atomic structure, magnesium gives the two electrons via an ionic bond in the case of magnesium oxide.

How to Draw Magnesium Oxide’s Lewis Structure (MgO)

Step 1: Determine the number of valence electrons already present in a magnesium oxide molecule: There are eight because two come from the Magnesium atom and six from the Oxygen atom.

Step 2: Determine how many valence electrons one Magnesium oxide molecule requires: Magnesium’s octet is already filled, therefore only the oxygen atom need two valence electrons.

Step 3: To begin drawing the Lewis structure, look for the centre atom: There can’t be a central atom because there won’t be any sharing of electrons.

Step 4: Look for an ionic bond between the magnesium and oxygen atoms: An ionic bond will develop between the atoms as magnesium donates two of its valence electrons from the 3s shell to fill the oxygen atom’s electron shortage.

Draw the Lewis structure of magnesium oxide (MgO) in step 5: Magnesium is a cation with a 2+ positive charge, whereas oxygen is an anion with a 2- negative charge, as seen in the diagram.

It’s worth noting that oxygen is a diatomic molecule, which means that two magnesium atoms must interact with one oxygen molecule to generate two molecules of magnesium oxide (MgO).

Furthermore, in the case of ionic bonding, the number of atoms donated or accepted is the same as the valency of the participating components.

Magnesium oxide (MgO) is an ionic substance, isn’t it?

Ionic compounds are generated when one atom provides valence electrons and the other accepts them, with no electron sharing between the two atoms.

The electrical force of attraction between the cation (positive) and anion (negative) ions holds these molecules together.

Because both participating atoms in magnesium oxide (MgO) are in the form of non-directional ions, they cannot have molecular geometry, hybridization, or a molecular orbital diagram.

The electronegativity idea can also be used to explain non-compliance with covalent characteristics and ionic bonding. According to the article, magnesium has an electronegativity of 1.2, while oxygen has an electronegativity of 3.5.

The oxygen atom attracts valence electrons towards itself because of its higher electronegativity value, whereas the magnesium atom donates valence electrons from its stable electronic state.

This is why, although having a stable atomic structure, magnesium is exposed to a higher energy level by the oxygen atom, which stabilises the oxygen by removing two electrons from the outermost shell.

Magnesium Oxide Molecular Structure (MgO)

Coordination geometry, which is directionless, is used to study the structure of ionic compounds. For example, the crystal lattice of magnesium oxide is strongly linked in an octahedral shape, resulting in its high melting temperature.

Furthermore, the crystal structure of magnesium oxide is Halite (cubic), with a lattice constant of 4.212.

The Valence Shell Electron Pair Repulsion (VSEPR) theory is not applicable to the coordination geometry that is not based on direction.

This indicates that the coordination geometry is relevant to the study of ions in crystal lattice theory.

Magnesium Oxide (MgO) is either polar or non-polar.

The concept of polarity only applies to covalent compounds with shared valence electrons. The resulting product, magnesium oxide, is not a metal since electrons are moved from magnesium to oxygen. When it comes to magnesium oxide, the concept of polarity does not apply.

Magnesium oxide can also be considered a polar molecule because of the charge separation that occurs when magnesium is a cation and oxygen is an anion.

Fajan’s rule for ionic bonding in magnesium oxide (MgO)

Fagan’s rule can be used to determine if the bonding is covalent or ionic. In the instance of magnesium oxide, the ionic bonds have a modest positive charge, a large cation, and a tiny anion (MgO).

When the polarising power of big cations (Magnesium 2+ ions) was investigated, it was discovered that their volume was greater. As a result, we may deduce that the charge density of the participating ions will be low due to the large volume.

As a result of the low charge density, the polarising power of the participating ions will be modest. The magnesium oxide (MgO) molecule is ionic in nature as a result of this situation.

When we looked at the polarizability of tiny anions (Oxygen 2- ions), we discovered that their effective nuclear charge, which holds the valence electrons, was higher. Because the valence electrons within the anions are loosely bound, they are easily polarised by both anion and cation, making magnesium oxide (MgO) more ionic in nature.


Magnesium oxide is a non-metal ionic compound that is created by electrostatic forces of attraction and does not obey the laws of covalent molecules such molecular geometry, hybridization, molecular orbital (MO) diagram, or polarity.

It is evident that magnesium is a cation with a 2+ charge, whereas oxygen is an anion due to its 2- charge. As a result, crystal lattice structure can be analysed instead of molecular geometry, and the magnesium oxide molecule can be called polar, but this trait is confined to covalently bound molecules only.

Read more: Lewis Structure, Geometry, Hybridization, and Polarity of SiCl2Br2

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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