Chlorine molecule consists of two chlorine atoms. At room temperature, it is a yellow gas with a pungent odor. It has a high density (3.2 g/mL).
The molecule is almost neutral (pH=7.4). It is slightly soluble in water.
The boiling and melting point of molecular chlorine are 239.11K and 171.6K, respectively. Cl2 is a covalent molecule as the bond is formed by sharing of electrons.
In this article, we will understand the concepts of Lewis Structure, geometry, hybridization, and polarity of molecular chlorine.
Cl2 Lewis Structure
Lewis Structure is a simple depiction of valence shell electrons in a molecule. It tells us how electrons are organized around specific atoms in a molecule.
It is also known as electron dot structures because electrons are represented by dots in this representation.
It does not explain geometry and bond formation accurately and is not used for the same. The best Lewis structure is the one in which octet rule and formal charges are satisfied.
Noble gases are considered to be inert and stable. All elements prefer to be stable, and hence one of the driving forces for bond formation is the attainment of noble gas-like configuration.
All elements prefer to have a configuration similar to that of noble gases in the main group.
The noble gases (except He) have 8 electrons in their valence shell, and hence atoms prefer to have 8 valence electrons. This gives rise to the octet rule.
It is a theoretical concept. It represents the charge on an atom if all the electrons in a chemical bond are shared equally.
A neutral molecule does not imply that all atoms in that molecule are neutral. There is a possibility of equal and opposite charges on the constituent atoms.
It is calculated using the following formula
Formal charge= (valence electrons in isolate state of a neutral atom) – (non-bonding valence electrons on atom) – (number of bonds formed by atom)
Steps to Draw the Lewis Structure of Cl2
1. Count the total number of valence shell electrons on the molecule
This is done by adding the valence shell electrons of all the constituent atoms.
|Atom||Atomic Number||Group Number||Valence electrons according to group number||Electronic configuration (E.C.)||Valence shell from E.C.||Valence electrons from E.C.|
|Two Cl||17||17||7||1s2 2s2 2p6 3s2 3p5||n=3||7|
|Total number of valence shell electrons= 7*2=14|
The Lewis dot structure for the Chlorine atom is as follows-
2. Choose a suitable central atom for the compound.
The central atom is supposed to be the least electronegative one out of the constituent atoms.
The central atom is supposed to share its electron density with all other atoms. Chlorine is a diatomic molecule. Both the atoms are the same.
There is no need to assign a central atom in a diatomic molecule because it is always linear.
3. Draw a skeletal diagram.
In this step, we have to arrange the constituent atoms suitably.
4. Arrange the valence electrons around the elemental symbols.
The total valence shell electrons (calculated in step 1) are placed according to bond formation.
5. Complete the octet of atoms by forming bonds.
Each Cl has seven valence electrons in the isolated state. Each Cl shares one electron with Cl to have a fully filled valence shell configuration.
6. Calculate the formal charge on all atoms.
The net charge on this compound is zero. Therefore, the sum of formal charge on three atoms should come out to be zero.
|Atom||Total number of valence
electrons in a free atom
|Total number of lone pairs||(Total number of bonding
Thus, the structure drawn in step 5 is the best Lewis structure for Cl2.
For a better understanding of the method for drawing the lewis structure of chlorine molecules, one can go through the following video.
Must Read belo articles on similar molecules.
Lewis structure does not aim to predict geometries. Geometries and shapes of compounds can be predicted by VSEPR theory.
VSEPR theory stands for valence shell electron pair repulsion theory.
According to VSEPR theory-
• The valence electron pairs repel each other, and this leads to instability. • To make the arrangement of the electrons stable, the repulsions between them have to be decreased.
• As a result, electrons align themselves so that the repulsion is the least, and the distance between them is maximum.
• The stable arrangement of the valence electron pairs of atoms helps determine the molecular geometry.
Valence shell electrons involved in bonding are known as bonding pairs of electrons (bp), and those valence shell electrons that are not involved in bonding are termed as lone pairs of electrons (lp).
For a diatomic compound, the shape is always linear, and there is no need to predict the shape using various theories.
However, the molecular geometry may or may not be the same as the shape. The geometry tells the orientation of the lone pair of electrons with respect to the bonded pair of electrons.
How to Predict Geometry of Cl2 using VSEPR
1. Count the number of valence shell electrons on the central atom and let it be equal to A (arbitrary variable)
In the case of Cl2, there is no central atom.
When there is no central atom, we choose the less electronegative element to be the central atom. Here, both the atoms are the same.
We can count valence shell electrons on any Cl. Cl has 7 valence electrons. (Shown in step1 of drawing lewis structure)
2. Count the number of side atoms and let it be equal to B (arbitrary variable).
In Cl2, there is one side atom (chlorine) and B=1
3. If the compound is charged, subtract the charge from B for the positively charged compound and add the charge to B for the negatively charged compound. This step can be avoided for neutral compounds.
In Cl2, there is no contribution of charge and B=1 only.
4. Add the contribution of side atoms and charge to the contribution of the central atom, i.e., A+B
For Cl2, A+B=8
5. Divide A+B by 2 to find total electron pairs affecting the shape.
For Cl2, there are 4 electron pairs.
6. Divide the total electron pairs as bonding and non-bonding. The bonding electron pair is equal to the number of side atoms.
For Cl2, there is one side atom. Thus, there are three non-bonding pairs of electrons and one bonding pair of electrons.
Using this information, we can predict geometry and shape using the following table. Electron geometry is tetrahedral, and the shape is linear.
The shape comes out to be accurate.
Since we do not have a central atom and VSEPR theory tells the geometry of side atoms with respect to the central atom. We consider the geometry and the shape of Cl2 to be linear.
The geometry and bonding of some polyatomic covalent compounds are explained using a unique concept called hybridization.
Hybridization is the mixing of atomic orbitals to form equivalent hybrid orbitals. It involves the redistribution of energy.
All atomic orbitals cannot be mixed. Only those orbitals that are similar in shape, size, and energy can mix and form hybrid orbitals.
For example, one 3s and two 3p orbitals can be mixed to form sp2 hybrid orbitals, while 2p and 6d cannot be mixed.
There is no literal mixing of orbitals; the operations are just carried on the wavefunction of orbitals. All compounds do not undergo hybridization like AsH3.
How to find hybridization?
Here, subscript 1 and 2 represents the first chlorine atom and the second chlorine atom.
The trick for calculating hybridization
We can also predict hybridization by calculating the total electron pairs, which we calculated using VSEPR to predict geometry.
For Cl2, the total domain comes out to be 4.
From the table, we see that for steric number 4, hybridization is sp3.
The polarity of a compound depends on the presence or absence of net dipole moment. The net dipole moment, in turn, depends on-
• Dipole moments of individual bonds
• The difference in electronegativities of the constituent atoms
• Geometry/Symmetry of compound
In molecule Cl2, there is only one Cl-Cl bond. The electronegativity of Cl is 3.16.
The Cl-Cl bond is non-polar since the electronegativity difference is zero. The dipole moment of the bond comes out to be zero.
In a diatomic molecule, a non-polar bond implies a non-polar molecule.
Must Read: Is Cl2 Polar or Nonpolar
Preparation of Chlorine gas
Heating concentrated HCl with metal oxide
When manganese dioxide reacts with concentrated HCl, Manganese chloride is formed along with chlorine gas.
MnO2 + HCl —-> MnCl2 + Cl2 + 2H2O
• Disinfectant in wastewater treatment.
• To control odor
• Chemical weapon in wars
• Production of paper and paper products
• Production of pesticides
• Manufacture of PVC, CFCs
• Bleaching agent
• Oxidizing agent
• Extraction of Au and Pt
• Chlorine gas is a diatomic molecule.
• Both chlorine atoms are bonded by one covalent bond.
• The Lewis structure drawn in the above section satisfies the octet rule and formal charge on the constituent atoms.
• It is a linear molecule.
• Cl2 is sp3 hybridized.
• It is a non-polar and covalent molecule.
• The gas finds its applications in various domains.
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