Magnesium fluoride or MgF2 is a stable non-hygroscopic compound that is merely soluble in dilute acids and insoluble in alcohol. It is an inorganic white crystalline salt that gets transparent on different wavelengths making it a suitable choice for optics. In the natural environment, magnesium fluoride occurs as sellaite which is clear to white prism-like salt.
On the commercial level, magnesium fluoride is formed when magnesium oxide reacts with any hydrogen fluoride (like ammonium bifluoride).
The reaction is mentioned below
MgO + (NH4)HF2 —–> MgF2 + NH3 + H2O
Being an important commercial compound, let’s study the Lewis structure and various chemical properties it shows because of valence electrons behavior.
What is Lewis Structure?
We can study the bonding between atoms of different molecules and the number of lone pairs of electrons within a molecule.
On a micro level, these structures depict the behavior of valence electrons while participating in bond formation. Lewis structures are drawn for the covalently bonded molecules as in the sharing of valence electrons takes place.
Magnesium fluoride (MgF2) is an anomaly as being an ionic compound, it shows covalent behavior because of which its Lewis structure can be studied.
It is so because the Lewis structure is drawn for such molecules where sharing of valence electrons takes place, which is the case with magnesium fluoride.
Also called electron dot structures, the Lewis diagrams help with studying the reasons behind the atoms within a molecule achieving the most stable position to remain unexcited.
What are Valence Electrons?
These electrons are present in the outermost shell of an atom and participate within the bond formation to produce a new molecule.
As valence electrons are present farthest from the nucleus of an atom, they do not feel any force of attraction.
Hence, by slightest excitation from other nearby valence electrons, they leave their shells and form a shared bond with other electrons having incomplete octet.
What is an Octet Rule?
This rule binds the number of valence electrons to a maximum of eight in the outermost shell of an atom.
By this rule, the maximum number of valence electrons that can accommodate in the outermost shell is interesting to realize that there are many groups in the periodic table which do not follow this rule and expand their outermost shell to accommodate more valence electrons.
One such group is 10 and the most common example is Sulfur.
Lewis Structure of Magnesium Fluoride
To begin with, studying the Lewis structure of magnesium fluoride molecule, first, we need to study the Lewis structure of magnesium and fluorine atoms.
The atomic number of magnesium is 12 where its electronic configuration is 1s2 2s2 2p6 3s2. This makes the total number of valence electrons in magnesium 2.
Whereas for fluorine the atomic number is 9 and its electronic configuration is 1s2 2s2 2p5. Here, the valence electrons in fluorine are 9.
Now, let’s begin with drawing the Lewis structure of magnesium fluoride (MgF2):
Step 1: Search for the maximum available valence electrons in one magnesium fluoride molecule: It is sixteen as two are with magnesium atom and fourteen are with two fluorine atoms.
Step 2: Look for valence electrons required by one magnesium fluoride molecule to complete its octet: It is eight as one each is needed by both the fluorine atoms and six are needed by the magnesium atom. Here, it is important to understand that two valence electrons will be donated by the magnesium atom and one will be received by each fluorine atom.
Step 3: Find the central atom: It is magnesium as this atom is present as a single entity.
Step 4: Find the type of bond formation occurring between the participating atoms: Only single bonds are forming between each magnesium and fluorine bond.
Step 5: Draw the Lewis structure by merging all the aforementioned points:
Molecular Geometry of Magnesium Fluoride (MgF2)
From the Lewis structure, it is clear that the molecular geometry of magnesium fluoride (MgF2) is linear.
As all the participating atoms are arranged in a straight line and at an angle of 180°, the tri-atomic MgF2 molecule has simplest of the structure.
The molecular geometry of magnesium fluoride can be studied in detail with the help of the Valence Shell Electron Pair Repulsion (VSEPR) theory.
As per this theory, a molecule acquires a linear structure when:
- bonding electron pairs are two
- lone pairs are zero
- electron domains are two
These conditions are fulfilled by the magnesium fluoride (MgF2) molecule
Hybridization in Magnesium Fluoride (MgF2) molecule
There will be no hybridization structure of magnesium fluorine as it is not a covalent compound. Magnesium has low electronegativity because of which when it bonds with a non-metal, it loses two valence electrons to get a +2 charge.
Whereas, fluorine atom has seven valence electrons and needs one to complete its octet. So, it gains one valence electron donated by the magnesium atom to get a -1 charge.
Here, the magnesium atom becomes a cation and fluorine becomes an anion.
It is because of this transfer of valence electrons and unequal charge cloud on the participating atoms, which makes magnesium fluoride an anomaly to be studied through the Lewis structure, besides being an ionic compound.
This is a classic example of an ionic compound showing a few covalent properties only because of sharing of valence electrons taking place between the participating magnesium and fluorine atoms.
Polarity in Magnesium Fluoride (MgF2)
Being an ionic compound, magnesium fluoride (MgF2) is highly polar. This can be confirmed with the help of the electronegativity values of the participating atoms.
As we know, electronegativity is a mathematical process of determining the tendency of the participating atoms to attract valence electrons towards themselves.
While determining the extent of electronegativity for polar or nonpolar molecules, the difference between the values of participating atoms must always be more than 0.4 till 1.7.
The electronegativity value of magnesium is 1.31 and that of fluorine atom is 3.98. Here, the difference is more than 2 making magnesium fluoride (MgF2) a strong polar compound.
Some Related Questions
What are ionic and covalent compounds?
Ionic compounds are produced when a metal compound reacts with non-metal compounds where covalent compounds are formed when two non-metal compounds react.
Here, it is crucial to understand that majority of the molecules will follow this rule but exceptions always exist in the chemistry.
- Metal + Nonmetal —> ionic compound
- Nonmetal + Nonmetal —> covalent compound
Is magnesium fluoride soluble in water?
Magnesium fluoride is highly insoluble in the water as it tends to agglomerate in the water and can be dewatered easily.
Magnesium fluoride (MgF2) is an exception as being an ionic compound, we study its Lewis structure. The Lewis structures are studied only for those compounds where valence electrons are being shared which is the case with magnesium fluoride (MgF2).
Here, it is important to know that this compound cannot have sp hybridization which is the case with molecules having linear geometry.
This is due to the fact that ions cannot produce a lattice structure as covalent compounds do. The linear geometry of the magnesium fluoride molecule has a 180° bond angle making it one of the simplest commercial molecules to be studied.