CH2Cl2 commonly known as dichloromethane or methylene chloride is a clear, colorless, volatile liquid with a slightly sweet odor. It is naturally obtained from volcanoes and macro algaes. Although not miscible with water but used as a solvent for many organic reactions. Many of the students have doubts regarding whether it is polar or nonpolar. In this article, we will study it with its fundamental reasons.
So, Is CH2Cl2 polar or nonpolar? CH2Cl2 is a polar molecule due to its tetrahedral geometrical shape and difference between the electronegativity of Carbon, Hydrogen and Chlorine atoms. This develops a dipole moment across C-Cl and C-H bonds and the entire molecule results in a net 1.67 D dipole moment.
Methyl Chloride is majorly produced by the emission through industries. It is produced by treating methane with chlorine at a high temperature of 400–500 °C.
Below are the chemical reactions that take place in the production of CH2Cl2.
CH4 + Cl2 —–heat——–> CH3Cl + HCl
CH3Cl + Cl2 ———heat——> CH2Cl2 + HCl
What are Polar and Nonpolar Molecules?
In order to determine and distinguish the polar or nonpolar nature of a molecule, there are below few key points in the subtopic that we will discuss.
First, let us have a brief idea about the polar and nonpolar molecules.
Polar Molecules: The molecules that have atoms sharing an unequal proportion of shared bonded electrons. This indicates that atoms differ in their electronegativity.
Higher electronegative atom attracts the shared bonded electrons slightly towards its side and gains a partial negative charge and other atom gains partial positive charge.
This difference in electronegativity generates a net dipole moment across the bond and makes it a polar.
If we talk about molecular geometry, it is generally seen that the shape of polar molecules is symmetrical or distorted.
Few examples of polar molecules are HBr, SO2, etc. You can check out the reason for the polarity of HBr.
According to most of the renowned books, In polar molecules, the electronegativity difference between the atoms is 0.5 to 1.6. And, the bond is nonpolar if the electronegativity difference is less than 0.5 or more than 1.6.
If the electronegativity of two atoms is different, the atom with a higher electronegativity pulls the shared bonded electrons closer to its side.
Therefore the atom with more electronegativity has a higher density of electrons around it and other atoms have lower electron density.
The degree of polarity varies from element to element, some elements are minimally polar whereas some are very strong polar in nature
Nonpolar Molecules: The molecules in which atoms share an equal proportion of shared bonded electron are nonpolar molecules.
No opposite poles generate in such atoms. The shape of such molecules is symmetrical.
It is possible that a nonpolar molecule has polar bonds within it but due to symmetric shape, the dipoles of such polar bonds get canceled by each other.
It means nonpolar molecules are formed when atoms share a polar bond arrangement in such a way that electric charges between them cancel out each other.
Few examples of nonpolar molecules are XeF2, CO2, etc. You can check out the reason for the non-polarity of XeF2.
All the inert gases and homonuclear diatomic molecules are nonpolar.
To identify the polarity and non-polarity of the compounds it is advisable to revise basic chemistry terminology like electronegativity, dipole moment, geometry, and shape of the molecule that will give more clarity.
Important terms of Chemistry
Electronegativity: Th term electronegativity depicts the strength of an atom to attract the electron pair towards its side.
This provides a more clear idea about the electronic configuration across the atoms in a molecule.
The more strongly an atom has an influence on the electrons, the larger is the value of its electronegativity.
Electrons in a polar bond are shifted nearer to the atom with more electronegativity.
As a result, higher electronegative atom gains a partial negative charge. Greater the difference in electronegativity, more polarized is the electron distribution across the molecule.
As per the periodic table, the electronegativity of the element increases from left to right and decreases down a group.
Therefore, the elements present in the right tend to have the highest electronegativities so halogen group elements are the most electronegative.
Metals are less electronegative elements, and the group 1 metals have the lowest electronegativities.
Dipole moment: Second important factor to measure the polarity of a chemical bond between two atoms in a molecule is a dipole moment.
It measures the separation of negative and positive charges in a system.
Mathematically, the dipole moment of a molecule can also be termed as the product of the magnitude of the charge on atoms and the distance between the centers of them.
The shape of the molecule: Another factor that determines the polarity is the shape of a molecule. The polarity or non-polarity of a complex molecule depends upon the overall center of overlapping positive and negative charges.
If a molecule is completely symmetric, then the dipole moment on each molecule will cancel out and make the molecule nonpolar.
A molecule is said to be polar if the structure of a molecule is not symmetrical.
Key points to check the polarity of a compound
- The strength of polarity is determined by comparing the electronegativity of bonding of atoms.
- Polarity can be measured by the shape and geometry of the molecules.
- Dipole moments also play an important role in deciding the polarity of a compound.
Why is CH2Cl2 a Polar molecule?
- C-Cl bonds are more polar as compared to C-H bonds.
- There is an unequal distribution of charges caused by the pull of electrons from the hydrogen atoms towards the chlorine atom as hydrogen atom has a lower electronegativity than chlorine atom.
- Chlorine has an ability to attract electrons, makes one side of dichloromethane partially positive, and the other side negative.
- The polarity of bonds is determined by comparing the electronegativity of the bonding atoms.
- In the case of dichloromethane electronegativity of all the bonding atoms are as follows
Hydrogen=2.2, carbon=2.5 and chlorine=3.1.
- So, electronegativity difference between C-H=0.3 and C-Cl=0.6. It proves that CH2Cl2 is polar but a moderate polar as the difference between their electronegativity is quite small.
- The total number of valence electrons in the CH2Cl2 molecule is 20. Carbon contains 4 valence electrons and hydrogen has 1 electron and chlorine has 7 valence electrons.
- So,there are total 20 valence electrons 4*1+1*2+7*2=20
- Both carbon atoms at the center form two bonds with 2 hydrogen and two bonds with 2 chlorine atoms. Out of 20 valence electrons, 8 electrons participate in bond formation.
- The bonds formed in dichloromethane are covalent as the central carbon atom is hybridized to form all the four bonds. The hybridization of carbon atoms is sp3.
- The molecular arrangement of the CH2Cl2 is in such a way that the carbon atom is situated at the center with sp3 hybridization. The geometry of CH2Cl2 is tetrahedral and the shape of the compound is trigonal pyramidal.
Applications of dichloromethane
- As volatile it is used as a solvent to remove paint or varnish coatings from a variety of surfaces and bathtub refinishing.
- In the aerosol industry, it is used to spray paint and insecticides.
- Most importantly used in the food industry to decaffeinate the coffee beans and tea leaves.
- It is used in processing spices and other flavorings for the food and beverage industries.
- In the pharmaceutical field, it is used as a solvent.
- CH2Cl2 is used to extract chemicals from plants to make steroids, vitamins, and antibiotics.
- CH2Cl2 is used to clean medical equipment without causing corrosion or heating damage.
- CH2Cl2 is used as a diluter of ink.
- Dichloromethane is used to degrease metal surfaces, airplane components, railway tracks, and equipment.
- Used in automotive products as a gasket removal and for prepping metal parts for new gaskets.
- In automotive industries vapor of CH2Cl2 helps to remove oils and grease from car transistor parts.
- Dichloromethane is used in the manufacture of synthetic fibers and photographic films.
Side effects of CH2Cl2
- It is noncombustible but at high temperatures, it emits toxic fumes of phosgene.
- Be careful while using it as it is highly toxic in nature.
- It irritates the eyes, throat, and nose.
- It disturbs the nervous system.
Precautions to handle CH2Cl2
- Wear an apron and full sleeves protective clothing.
- Wear proper footwear to cover the entire foot.
- Always wear PPE kit, goggles, and safety gloves.
- Work in a well-ventilated area.
- As it is highly volatile, so should be stored in a cool, dry area in tightly closed and labeled containers.
- And needs to be kept away from metals, light, and any source of heat or ignition.
In nutshell we found that CH2Cl2 is polar because of the following reasons:–
- The shape of its trigonal pyramidal.
- The geometry of the compound is tetrahedral.
- Dipole moments between C-H and C-Cl do not cancel.
- Electronegativity between C-H and C-Cl is 0.4 and 0.6 respectively.
Overexposure to it causes cancer, coughing, wheezing, shortness of breath and inhalation can lead to headaches, mental confusion, nausea, vomiting, dizziness, and fatigue.