MgCO3 Lewis Structure& Characteristics: 17 Complete Facts

MgCO3 is a white or colorless inorganic salt having molar mass 84.3139 g/mol and density 2.96 g/cm3. Let us explore more related to its lewis structure and properties.

MgCO3 is a trigonal shaped solid crystalline ionic compound containing two oppositely charged ions (Mg2+ and CO32-). But it also incorporates covalent bonding (in CO32-). It is dissolved in water, acid and aqueous carbon dioxide and the aqueous solution of it is slightly alkaline rather than acidic.

Let us discuss about the structural properties of MgCO3.

How to draw MgCO3 lewis structure?

Lewis structure is a structural representation of any molecule showing nonbonding electrons around the respective atoms. Let us talk about this.

Determining the valence electrons:

The lewis structure of MgCO3 contains three types of atoms, Magnesium (Mg), carbon (C), and oxygen (O) which have two, four and six electrons in their respective valence shell.

Finding out the bonding electrons:  

CO32- in MgCO3 has total four covalent bonds (two single and one double) and there is one ionic bond between Mg and CO3. Therefore, total (5×2) = 10 electrons are involved as bonding electrons.

Determining the nonbonding electrons:

Only CO32- in MgCO3 carry lone pairs (lone pairs of oxygen). Total 10 electrons are left as nonbonding electrons.

MgCO3 Lewis Structure

MgCO3 Lewis Structure Resonance

Lewis structure resonance is the combination of several structures of a molecule, showing bonding between the atoms in that molecule. Let us discuss more about it.

MgCO3 lewis resonance structure shows three different resonance structure of carbonate ion (CO32-), involving same number of covalent bonds and charge. Resonance structure can only be observed in covalent compounds or covalent portion. All the three resonance structures in CO32- are equivalent.

Drawing resonance structure is very much significant in chemistry because these structures help to determine the most stable structure as well as the shape of the molecule. It also has a contribution in calculating of formal charges of each of the atom.

MgCO3 Resonance Structure

MgCO3 Lewis Structure Shape

Shape of any molecule can be determined from the hybridization of central atom and repulsion between the lone pairs and bond pairs. Let us comment on the shape of MgCO3.

MgCO3 lewis structure shape contains a crystallographic structure with a trigonal shape. It contains Mg2+ and CO32- ions. The carbonate ion is trigonal planar in shape. Carbon is sp2 hybridized in CO32-. One s and two p orbitals of carbon are involved in this hybridization in carbonate ion.

Carbon atom is attached with three oxygen atoms (two oxygen atoms are negatively charged and another one is neutral) by two single and one double bonds. But all the bonds are chemically equivalent having equal bond length.

Thus, all the resonance structures contribute to the hybrid structure equally. So, the geometry and as well as the shape of this molecule is trigonal planar.

MgCO3 Lewis Structure Formal Charge

Formal charge is calculated only in the covalently bonded molecule to determine the most stable lewis structure. Let us calculate the formal charge using the following rule.

  • MgCO3 formal charge calculation= Total number of valance electrons – number of electrons remain as nonbonded – (number of electrons involved in bond formation/2)
  • Formal charge of carbon = 4 – 0 – (8/2) = 0
  • Formal charge of each of the oxygen attached by single bond with carbon = 6 – 6 – (2/2) = -1
  • Formal charge of the oxygen atom attached through double bond with carbon = 6 – 4 – (4/2) = 0

The carbonate ion in MgCO3 carries two negative charges but this charge is neutralized by the +2 charge of Mg2+. Therefore, this compound is neutral, carrying no charge as a whole.

MgCO3 Lewis Structure Angle

Lewis structure angle denotes the angle between the central atom and the two substituent atoms or groups. Let us discover about the angle in detail.

MgCO3 lewis structure angle shows bond angle 1200. It contains carbonate ion which is sp2 hybridized. This is the ideal bond angle of any molecule having trigonal planar geometry. Bond angle basically depends upon the hybridization as well as the shape of the molecule.

But this bond angle can be deviated if any repulsion is present in molecule like lone pair-lone pair, bond pair-lone pair and bond pair-bond pair repulsion. This molecule is free from these repulsive factors because the central atom, carbon has no nonbonding electrons.

MgCO3 Lewis Structure Octet Rule

Octet rule describes having same number of valence electrons in any atom’s outer shell as its nearest noble gas. Let us understand if MgCO3 obeys octet rule or not.

The lewis structure of MgCO3 decides if it obeys octet rule or not. Mg (s block) has 12 electrons and it achieves its nearest noble gas valence shell electron configuration in this compound. Rest of the covalent part CO32- also fulfils this rule because all of them are main block (s and p block) element.

In the CO32-, carbon has 4 valence electrons and when it is involved in bonding with the 4 oxygen atoms, it gets four more electrons from the oxygen and octet rule is satisfied. The negatively charged oxygen are attached through covalent bond with the carbon and the bonding electrons are mutually shared between them.

The neutral oxygen atom is bonded through one sigma and one pi with the carbon atom and the four electrons of the double bond (one sigma and one pi) are mutually shared between them and it also gets its nearest noble gas (Ne) like electron configuration.

MgCO3 Lewis structure Lone Pairs

Lone pairs indicate those electrons which have no contribution in bond formation. Therefore, they are called as nonbonding electrons. Let us comment on the lone pairs of MgCO3.

MgCO3 lewis structure lone pairs can be determined by using an easy calculation like the following-

  • Formula of calculation of nonbonded electron = Total number of valance electron – number of bonded electrons.
  • Nonbonding electrons of carbon = 4 – 4 = 0
  • Nonbonding electrons of the negatively charged oxygen atom = 6 – 0 = 6
  • Nonbonding electrons of the neutral oxygen atom = 6 – 2 = 4
  • Therefore, total number of nonbonding electrons in MgCO3 = (2×6) + 4 = 16 or 8 lone pairs.

MgCO3 Valence Electrons

Valence electrons indicate the electrons of outer most shell of any atom and they are the most reactive with respect to the inner shell electrons. Let us discuss in detail on it.

The valence electrons of MgCO3 can be determined from the electron configuration of each of the constituent atoms. Mg is an alkaline earth metal and it has 2 electrons in its valence shell. Carbon and oxygen being p block element, have four and six valence electrons respectively.

Mg is a s block alkaline earth metal with electron configuration [Ne] 3s2. Carbon and oxygen both are p block element with electron configuration [He] 2s2 2p2 and [He] 2s2 2p4. From the configuration, it is clear that Mg, carbon and oxygen have 2, 4 and 6 electrons respectively.

MgCO3 Hybridization

Hybridization is the mixing of two or more atomic orbitals to form a new hybrid orbital. Let us discover more on the hybridization of MgCO3.

In the hybridization of MgCO3, we can see that the central carbon atom of carbonate ion is sp2 hybridized.  Four electrons of one s and three p orbitals of carbon are involved in this hybridization with the three oxygen atoms. This hybridization makes the molecule trigonal planar in shape.

There is no lone pair in the central atom, thus, geometry is shame as its shape, trigonal planar and bond angle, 1200 in carbonate ion.

Is MgCO3 covalent or ionic?

To know about whether MgCO3 is covalent or ionic, the basic difference between them should be cleared. Let us talk about it in detail.

MgCO3 is such a compound which incorporates both the covalent and ionic bond in its structure. Mg2+ is connected with carbonate ion through ionic interaction. But the carbon is attached with three oxygen atoms through covalent bonds.

Why MgCO3 is covalent as well as ionic compound?

The presence of covalent as well as ionic interaction make it covalent as well as ionic compound. Let us explore it in brief.

MgCO3 is covalent as well as ionic because it contains two oppositely charged atoms and ionic interaction (coloumbic) is present in between of them. On the other hand, carbon atom in CO32- is bonded with the three oxygen atoms through four covalent bonds (three sigma and one pi).

How MgCO3 is covalent as well as ionic compound?

Covalency arises due to the mutual sharing but ionic interaction arises due to permanent transferring of electrons. Let us discuss about it.

The bonding electrons in CO32- are mutually shared between the bond forming atoms, carbon and oxygen. Thus, all these four bonds in CO32- are considered as covalent bonds. But the interaction between Mg2+ and CO32- is defined as ionic interaction because of the two oppositely charged ions.

Is MgCO3 a solid?

Whether any molecule is solid or liquid or gas can be decided from its boiling point. Let us talk about it.

MgCO3 is a white solid under ambient conditions. It is a trigonal shaped crystallographic lattice structure.

Why and how MgCO3 is a solid compound?

MgCO3 has melting point 9900 C which indicates the solid phase of it. Let us discuss why and how it is solid.

MgCO3 is solid because a strong ionic interaction is present between Mg2+ and CO32-. The unit cells of it are densely attached with each other. Therefore, a huge amount of heat energy is required to make it liquid. So, it appears as a solid substance under room temperature.

Solid MgCO3.
Image Credit: Wikimedia Commons.

Is MgCO3 soluble in water?

Solubility of any compound depends upon the nature of the substance as well as the lattice energy. Let us discover it in detail.

MgCO3 is sparingly soluble in water and the aqueous solution is slightly alkaline in nature. The reason for being sparingly soluble is the high lattice energy of magnesium carbonate.

Why MgCO3 is soluble in water?

If the nature of solute and solvent is similar then the solute will be soluble in that particular solvent. Let us explore it.

MgCO3 is soluble in water because MgCO3 is an ionic and polar compound and water is as well as a polar solvent. Therefore, MgCO3 is soluble in water because of the similar interaction type.

How MgCO3 is soluble in water?

Due to having polar nature, MgCO3 can be dissolved in water. Let us talk about this.

MgCO3 is soluble in water because the constituent atoms, Mg2+ and CO32- are hydrated by the water molecules. The hydrogen end lies in the surroundings of the negatively charged substituent, carbonate ion and the oxygen end will hydrate the Mg2+ end of MgCO3. For this interaction, MgCO3 is dissolved in water.

Is MgCO3 polar or nonpolar?

A molecule is polar or nonpolar can be decided from its substituent atoms. Let us investigate about it.

MgCO3 is an ionic as well as polar compound. Due to presence of two oppositely charged ions, MgCO3 is polar and soluble in polar solvent.

Why and how MgCO3 is a polar compound?

The ionic interaction in MgCO3 makes it a polar compound. Let us discuss on it.

MgCO3 is an ionic substance. An ionic interaction is working between magnesium and carbonate ion which makes it polar solid substance. MgCO3 can be soluble in water (polar solvent) due to the hydration of the atoms by the water molecules.


Magnesium carbonate containing Mg2+ and CO32- ions is a polar and solid compound. It is used in the calcination process for the formation of calcium oxide. It has also a significant use in fire extinguishing, flooring and production of toothpaste, cosmetics etc.

Aditi Roy

Hello, I am Aditi Ray, a chemistry SME on this platform. I have completed graduation in Chemistry from the University of Calcutta and post graduation from Techno India University with a specialization in Inorganic Chemistry. I am very happy to be a part of the Lambdageeks family and I would like to explain the subject in a simplistic way. Let's connect through LinkedIn-

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