MgCl2 is an ionic halide salt consisting of magnesium and chlorine elements. It is inorganic in nature that may appear as a white or colorless crystalline solid compound. In its anhydrous form, it consists of about 25.5% Mg by mass and has a molar mass of about 95.211 g/mol.
It has a boiling point of 1685 K and a density of 2.32 g/cc.
We can extract hydrated MgCl2 from brine. Also, we can witness varying degrees of bitterness in MgCl2 solutions which in turn depends on the percentage of Mg present in them.
Magnesium chloride has a wide range of applications.
It is used for ice-control in low-temperature de-icing of roads and pavements. MgCl2 is used for dust control and wind erosion mitigation purposes.
Other than this, we get to see anhydrous magnesium chloride used as a precursor to metallic Mg.
MgCl2 —–> Mg + Cl2
In this universe, we have a vast range of elements that come together to create different varieties of chemical compounds.
Atoms get attracted and form several molecules of varied chemical composition.
The study of atomic attraction that results in the formation of products is known as chemical bonding.
Chemical bonding is an interesting and notable concept of chemistry and we have several types of bonds to discuss and understand. We can also get an idea about the chemical and physical properties of a compound from this concept.
Here, in this article, we will discuss the nature of chemical bonding inside a molecule of MgCl2.
A Brief Intro
Lewis Structure is the first and foremost step towards understanding the concept of bonding.
To find the most suitable Lewis Structure of a given molecule or ionic composition, we have to sketch skeletal electron-dot diagrams of the constituent elements along with their valence electrons (electrons present in the outermost shell).
This is therefore a 2D graphical representation of a molecule where we find out the type of bonds that are present in between atomic elements.
Let us now draw the Lewis Structure diagram for MgCl2.
Lewis Structure of MgCl2
This is a diagram of the Periodic Table. As we can see, Mg belongs to group 2 and has an atomic number of 12 whereas Cl belongs to group 17 and has an atomic number of 17.
Mg has 2 valence electrons whereas Cl has 7 valence electrons.
The total number of valence electrons in a molecule of magnesium chloride = 2*1 + 7*2 = 16.
Magnesium, as we all know, is an alkaline earth metal. Chlorine, on the other hand, is a halogen and therefore a non-metal.
This combination results in an ionic compound and therefore the bond type is ionic and not covalent.
In covalent bonds, we see sharing of electron pairs but in ionic bonds, we will see electron transfer.
But in both cases, we work towards the fulfillment of the octet i.e. the octet rule.
Octet Rule: The main group elements present in groups 1-17 tend to have the valence shell octet configuration of the noble gas elements.
Now, here, let us draw the sketch:
If we put the valence electrons accordingly, the sketch looks like this:
Both the Chlorine atoms are only one electron short of achieving the octet configuration whereas Mg has only 2 valence electrons.
The electronic configuration of Mg is:
Mg: 1s2 2s2 2p6 3s2
The electronic configuration of Cl is:
Cl: 1s2 2s2 2p6 3s2 3p5
Magnesium will transfer each of its valence electrons to both the Cl atoms.
Now, the electron configuration of Mg will be:
Mg: 1s2 2s2 2p6
Or, Mg: [ Ne ]
And, the electron configuration of each Cl atom becomes:
Cl:1s2 2s2 2p6 3s2 3p6 or Cl: [ Ar ]
Since Mg lost two electrons, it becomes cationic with +2 positive charge and Cl becomes Cl- by gaining one electron.
This is the most suitable Lewis Structure diagrammatic representation of MgCl2.
We use brackets to describe the ionic nature and put the negative and positive charges.
Polarity is an important physical property of chemical compounds that we are going to discuss here.
It deals with the separation of electric charges between the atoms inside a molecular structure that result in dipole moments due to a difference in electronegativity values.
If constituent atoms have a difference in electronegativity values, it means that there will be unequal sharing of electrons. This leads to the formation of partial positive and negative charges on the electropositive and electronegative elements respectively which forms a polar bond.
Polarity is therefore strongly connected to the other concept, electronegativity.
Polarity of MgCl2
We have a diagram of the Pauling Electronegativity Chart from where we can easily find out the corresponding values of each element.
In each bond of Mg-Cl present inside a molecule of MgCl2, we have Mg bearing an electronegativity value of 1.31 whereas Cl bears a value of 3.16.
∴ the difference in the value of electronegativity = 3.16 – 1.13 = 1.85.
As the difference in electronegativity between atoms increases, the ionic character of the bond increases, and usually, a difference more than 1.7-2 is considered to be of ionic nature.
Mg-Cl is therefore an ionic bond and the molecule is polar-ionic in nature. Hence, we have a polar molecule.
“Like dissolves like”- hence, MgCl2 is soluble in water which is a polar solvent carrying partial charges on hydrogen and oxygen. Hydrogen carries 𝛅+ whereas oxygen carries 𝛅-. The positively charged Mg coordinates with oxygen whereas Cl coordinates with hydrogen and thus MgCl2 dissolves in water.
KCl is also one such ionic compound. I have written an article on it too. You can check it out on KCl Lewis Structure, Geometry, Hybridization.
Molecular geometry for covalent compounds refers to the 3-dimensional shape of molecules that we decipher from Lewis Structure with the help of VSEPR or Valence Shell Electron Pair Repulsion Theory.
This theory deals with the concept of electron sharing arrangement and therefore not applicable for ionic compounds where bonds form via transfer of electrons resulting in positive and negative charges.
VSEPR is only applicable for those ionic compounds where there is polyatomic ion arrangement like nitrates and carbonates.
However, in the case of MgCl2, we cannot use this model and we do not have a molecular geometry.
Magnesium chloride forms lattice structures for their crystalline arrangement. The coordination geometry refers to the geometric pattern arrangement of atoms around the central atom. For MgCl2, it is a 6-coordinate octahedral.
The crystal structure is similar to that of Cadmium chloride (CdCl2).
Orbital hybridization is a concept to describe the process of chemical bonding inside several molecular compositions.
In this model, we discuss the combination of several atomic orbitals of the same atoms having equivalent energies to form hybridized orbitals that take part in bonding.
Hybridization is an important model to explain the covalent bonding nature.
However, in ionic compounds like MgCl2, we find that molecules are formed via the complete transfer of electrons from the electropositive atom to the comparatively electronegative atom to result in ions.
Here, electrostatic attraction comes into play and ionic bonds formed are non-directional. We do not need to deal with energies of orbitals in this case and thus hybridization is not required.
In this article, we have discussed the ionic halide, Magnesium Chloride (MgCl2). To discuss the nature and type of bond formation, we have included the steps to draw the Lewis Structure. Other than this, we have talked about the polarity and coordination geometry of MgCl2.