The chemical formula CoCl2 represents Cobalt (II) Chloride. It is an inorganic compound that comprises Cobalt and Chlorine atoms. CoCl2 is a crystalline solid that is sky-blue in color. It is readily soluble in water, alcohol, and acetone.
It occurs at different levels of hydration as dehydrates and hexahydrates. These versions of the salt are purple and pink, respectively. This ease of hydration and dehydration makes Cobalt Dichloride a good indicator of hydration in desiccants and humidity.
CoCl2 occurs freely in nature and can be found in rocks and minerals. Cobalt is essential to most large-bodied organisms, but an excess of the element can cause adverse effects. Cobalt Dichloride has been marked as a ‘substance of concern’ and a potential carcinogen by the European Chemical Agency.
It has a history of being used to induce hypoxia-like responses such as erythropoiesis.
It has the following properties:
| Name of the molecule | Cobalt Dichloride (CoCl2) |
| No. of valence electrons | 2 + (7 x 2) = 16 valence electrons |
| Hybridization of the central atom | sp |
| Bond Angles | 180° |
| Molecular Geometry of CoCl2 | Linear Molecular Geometry |
Contents
CoCl2 Valence Electrons
To form Lewis structures, we need to know more about the building blocks that help make them. These building blocks are the valence electrons contributed by the constituent atoms. Valence electrons are those electrons that are available to be used during bond formation.
These electrons are present in the outermost shell, where the force of attraction from the nucleus is the weakest. This allows the electrons to break free of the atom during exchanges.
CoCl2 comprises a Cobalt atom flanked by two Chlorine atoms on either side.
Being in group 9 (transition metals) of the periodic table, Cobalt has an electronic configuration of [Ar] 3d74s2. Therefore, a single Cobalt atom contributes 2 x 1 = 2 Valence electrons.
Being in group 7 of the periodic table, Chlorine has seven valence electrons with a valency of -1. Chlorine’s electronic configuration is given by [Ne]3s23p5. The possibility of electrons in its d shell makes it hypervalent.
Therefore, the two Chlorine atoms present in CoCl2 contribute 7 x 2 = 14 valence electrons.
Thus, the total number of valence electrons in Cobalt Dichloride [CoCl2] is given by:
2[Co] + 14[Cl] = 16 valence electrons.
CoCl2 Lewis Structure
The Lewis structure of a compound helps predict many of its properties. Its molecular geometry, polarity, and reactivity can be determined by observing the corresponding Lewis structure.
The first step to obtaining the Lewis structure is to calculate the number of valence electrons available. As discussed in the previous section, valence electrons are integral and act as the building blocks of the structure. They help facilitate bond formation.
The Cobalt and Chlorine atoms present contribute 16 valence electrons by virtue of their electronic configuration.
The next step is to determine the central atom and arrange the remaining elements around the central atom. In this case, Cobalt acts as the central atom due to its relatively electropositive nature. The two Chlorine atoms flank the Cobalt atom on either side.
We then use the valence electrons to form covalent bonds between the atoms. Two valence electrons are used to create a Co-Cl bond. This is represented in the figure below.
Having used four valence electrons for bond formation, we now have 12 valence electrons available to us. These are then used to fulfill the octets for the outer atoms, i.e., the two Chlorine atoms. All 12 valence electrons are used in this process.
It can be observed above that Cobalt does not fulfill its octet requirements. The temptation here would be to establish a double bond on either side to obtain a Cobalt octet. However, we must first check for stability.
To check if this structure is indeed stable, we must calculate its formal charges.
Formal charges for an element/structure help determine its most stable Lewis Structure state. It is determined such that the elemental charge on each atom is closest to zero.
FC = Valence Electrons – Non-bonding electrons – (Bonding electrons ÷ 2)
In this case,
| Element | V | N | B/2 | FC |
| Co | 2 | 0 | 4/2 | 0 |
| Cl | 6 | 6 | 2/2 | 0 |
| CL | 6 | 6 | 2/2 | 0 |
The formal charges being 0 for all of the atoms in the CoCl2 molecule tells us that the Lewis dot structure presented above is stable.
Thus, the Lewis structure of CoCl2 is an exception to the octet rule.
Therefore, the Lewis Structure for the CoCl2 is represented as follows:
CoCl2 Hybridization
To determine the hybridization of Cobalt Dichloride, we first determine the number of electrons domains. Lone pairs and covalent bonds with other atoms contribute to being electron domains.
Two domains give us an sp hybridization. Three domains give us and sp2 hybridization and so on.
Therefore, in this case, there are two covalent bonds present, i.e., the two Co-Cl bonds. This gives us an sp hybridization state.
Cobalt Dichloride [CoCl2] has a hybridization of sp.
CoCl2 Molecular Geometry and Bond Angles
To determine the molecular geometry of CoCl2, we observe the Lewis structure shown above. It can be seen that Cobalt is the central atom while two Chlorine atoms surround it on either side.
According to VSEPR, the two Chlorine atoms repel each other and are driven apart. This leads to a linear structure.
We can determine the molecular geometry using the A-X-N method.
‘A’ represents the central atom Cobalt. Therefore, ‘A’ = 1.
‘X’ represents the number of atoms bonded to the central atom. In this case, two Chlorine atoms are bonded to the central Cobalt atom.
Therefore, X =2.
‘N’ represents the number of lone pairs attached to the central atom. In this case, N = 0 since there are no lone pairs present.
Therefore, that would give us AX2 for the CoCl2 molecule. N can be ignored since there are no lone pairs.
From the A-X-N table below, we can determine the molecular geometry for CoCl2.
| Formula | Shape | Bond Angle (Theoretical) |
| AX2 | Linear | 180 |
| AX3 | Trigonal Planar | 120 |
| AX4 | Tetrahedral | 109.5 |
| AX5 | Trigonal Bipyrimidal | 120, 90 |
| AX6 | Octahedral | 90 |
| AX2N | Bent | 120 |
| AX2N2 | Bent | 109.5 |
From the above table, it can be observed that an AX2 arrangement corresponds to a Linear Molecular geometry and a Bond angle of 180°.
Concluding Remarks
Let’s quickly summarize the salient features of CoCl2
- CoCl2 comprises a central Cobalt atom bonded to two Chlorine atoms on either side.
- In its most stable state, the structure is an exception to the octet rule as Cobalt’s octet requirements are not fulfilled.
- The hybridization of Cobalt Dichloride is sp since there are only two electron regions.
- CoCl2 has a Linear molecular structure with bond angles of 180°.
