Chloromethane (CH3Cl) Lewis dot structure, molecular
geometry or shape, electron geometry, bond angle,
hybridization, formal charges, polar vs non-polar
CH3Cl is the chemical formula for chloromethane, also known as methyl chloride. It is an odorless, colorless, flammable chemical compound that exists as a gas at room temperature and pressure.
CH3Cl belongs to the haloalkane family. It is naturally present in the atmosphere as well as released into the air via its usage as an industrial chemical and a refrigerant.
In this article, we will talk about how to draw the Lewis dot structure of CH3Cl, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar vs non-polar concept, etc.
The Lewis structure of CH3Cl consists of a carbon (C) atom at the center which is bonded to three hydrogens (H) atoms and one atom of chlorine (Cl). There are a total of 4 electron density regions around the central C atom in the CH3Cl Lewis structure.
All the 4 electron density regions are comprised of bond pairs thus there is no lone pair of electrons on the central C-atom in CH3Cl.
Below is a step-by-step guide that you can follow to draw the Lewis dot structure of chloromethane (CH3Cl).
Steps for drawing the Lewis dot structure of CH3Cl
1. Count the total valence electrons in CH3Cl
The first step while drawing the Lewis structure of a molecule is to count the total valence electrons present in it. The number of valence electrons present in an elemental atom can be easily determined by identifying its Group number from the Periodic Table of elements.
As there are atoms from three different elements of the Periodic Table in CH3Cl. So you need to look for these elements in the Periodic Table.
Carbon (C) belongs to Group IV A (or 14) so it has a total of 4 valence electrons. Chlorine (Cl) is present in Group VII A (or 17) so it has 7 valence electrons while hydrogen (H) lies at the top of the Periodic Table containing a single valence electron only.
The CH3Cl molecule consists of 1 C-atom, 1 Cl-atom, and 3 H-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of CH3Cl = 1(4) + 7 + 1(3) = 14 valence electrons.
2. Choose the central atom
In this second step, usually the least electronegative atom out of all the concerned atoms is chosen as the central atom.
This is because the least electronegative atom is the one that is most likely to share its electrons with the atoms spread around it.
Chlorine is more electronegative than both carbon and hydrogen. Hydrogen (E.N = 2.20) is less electronegative than carbon (E.N = 2.55) but it cannot be chosen as the central atom because a hydrogen (H) atom can accommodate only 2 electrons so it can form a bond with a single adjacent atom only. This denotes that H is always placed as an outer atom in a Lewis structure.
As a result, the carbon (C) atom is chosen as the central atom in the Lewis dot structure of chloromethane (CH3Cl) while one Cl and three H atoms are placed around it as outer atoms, as shown in the figure below.
3. Connect outer atoms with the central atom
Now we need to connect the outer atoms with the central atom of the Lewis structure using single straight lines.
As three hydrogens and one chlorine atom are the outer atoms in the Lewis structure of chloromethane so these atoms are joined to the central C-atom using straight lines.
Each straight line represents a single covalent bond i.e., a bond pair containing 2 electrons. There are a total of 4 single bonds in the above diagram.
As 4(2) = 8, that means 8 valence electrons are already consumed out of the 14 initially available.
4. Complete the duplet and/or octet of the outer atoms
As we already identified, the hydrogen and chlorine atoms are the outer atoms in the Lewis dot structure of CH3Cl.
Each hydrogen (H) atom requires a total of 2 valence electrons in order to achieve a stable duplet electronic configuration.
A C-H single bond already represents 2 valence electrons around each H-atom. This means all three H-atoms already have a complete duplet in the Lewis structure drawn till yet. Thus, we do not need to make any changes with regard to the hydrogen atoms in this structure.
In contrast to that, a Cl-atom needs a total of 8 valence electrons to achieve a stable octet electronic configuration. A C-Cl bond represents 2 electrons which denotes the outer Cl atom needs 6 more electrons to complete its octet. Consequently, 6 valence electrons are placed as 3 lone pairs on the chlorine (Cl) atom in the CH3Cl Lewis structure, as shown below.
5. Complete the octet of the central atom
In the Lewis structure drawn till step 4, the central carbon (C) atom has four single bonds around it i.e., 3 C-H single bonds and 1 C-Cl single bond. Four single covalent bonds represent a total of 4(2) = 8 valence electrons. In short, the central C-atom already has a complete octet electronic configuration.
Total valence electrons used till step 5 = 4 single bonds + electrons placed around the Cl-atom, shown as dots = 4(2) + 6 = 14 valence electrons.
Total valence electrons – electrons used till step 5 = 14 – 14 = 0 valence electrons.
All the valence electrons initially available are now used up therefore there is no lone pair of electrons on the central C-atom in the Lewis dot structure of CH3Cl.
The final step is to check the stability of the Lewis structure obtained in this step. Let us do that using the formal charge concept.
6. Check the stability of the CH3Cl Lewis structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charge can be calculated using the formula given below.
The absence of any formal charges on the bonded atoms in the CH3Cl Lewis structure marks the incredible stability of this structure.
Now that we have obtained the correct and best Lewis representation of chloromethane (CH3Cl), let us move ahead and discuss its shape, geometry, and other interesting chemistry facts.
What are the electron and molecular geometry of CH3Cl?
The chloromethane (CH3Cl) molecule has an identical electron geometry and molecular geometry or shape i.e., tetrahedral. There are a total of 4 electron density regions around the central C-atom in CH3Cl and there is no lone pair of electrons on this central atom.
Thus, there is no distortion witnessed in the shape and geometry of the molecule.
Molecular geometry of CH3Cl
The molecular geometry or shape of chloromethane (CH3Cl) is tetrahedral. The absence of any lone pair of electrons on the central C-atom in CH3Cl means there are no lone pair-lone pair and lone pair-bond pair electronic repulsions present in the molecule.
C-H, C-H, and C-H and C-Cl bond pair-bond pair repulsive effect exist which makes the bonded electron pairs occupy the four corners of a tetrahedron, as shown in the figure below.
Electron geometry of CH3Cl
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In CH3Cl, there are 4 single bonds around the central carbon atom which makes a total of 4 electron density regions. Thus, its electron geometry is also tetrahedral.
A shortcut to finding the electron and the molecular geometry of a molecule is by using the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the geometry or shape of a molecule using the VSEPR concept.
AXN notation for CH3Cl molecule
A in the AXN formula represents the central atom. In the CH3Cl molecule, a carbon (C) atom is present at the center so A = C.
X denotes the atoms bonded to the central atom. In CH3Cl, three hydrogens (H) and one chlorine (Cl) atom are bonded to the central carbon so X = 3+1 = 4.
N stands for the lone pairs present on the central atom. As per the Lewis structure of CH3Cl, there are no lone pairs of electrons on the central carbon so N = 0.
As a result, the AXN generic formula for CH3Cl is AX4.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX4 generic formula is identical to its electron pair geometry i.e., tetrahedral, as we already noted down for chloromethane (CH3Cl).
Hybridization of CH3Cl
The central carbon (C) atom in the chloromethane (CH3Cl) molecule is sp3 hybridized.
The electronic configuration of carbon is 1s2 2s2 2p2.
During chemical bonding, the 2s electrons of carbon get unpaired. One of the two electrons shifts to the empty 2p atomic orbital.
The 2s orbital and three half-filled 2p atomic orbitals of carbon consequently hybridize to yield four sp3 hybrid orbitals. Each sp3 hybrid orbital is equivalent and contains a single electron only. It possesses a 25% s character and a 75% p-character.
Three of the four sp3 hybrid orbitals of carbon form C-H sigma (σ) bonds by overlapping with the s-orbitals of the hydrogen atoms. The remaining sp3 hybrid orbital of carbon forms the C-Cl sigma (σ) bond by overlapping with the p-orbital of the chlorine atom in CH3Cl.
Refer to the figure drawn below.
Another shortcut to finding the hybridization present in a molecule is by using its steric number against the table given below. The steric number of central C in CH3Cl is 4 so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The CH3Cl bond angle
The bonded atoms in a CH3Cl molecule possess a mutual bond angle of 109.5°, as expected in a symmetrical tetrahedral shape. The C-Cl bond length is 134 pm while each C-H bond length is 107 pm in CH3Cl.
The C-X bond length is greater than a C-H bond length in halo alkanes where X is a halogen. This is because of the greater electronegativity of the halogen atom that attracts the shared C-X electron cloud towards itself to a greater extent.
According to Pauling’s electronegativity scale, a covalent bond is considered polar if the concerned atoms have an electronegativity difference greater than 0.5 units. An electronegativity difference of 0.35 units exists between a carbon (E.N = 2.55) and a hydrogen (E.N = 2.20). Therefore, the C-H bond is only weakly polar.
In contrast to that, the chlorine atom is highly electronegative. An electronegativity difference of 0.61 units exists between the carbon and chlorine (E.N = 3.16) atoms. Hence the C-Cl bond is polar in nature and it possesses a specific dipole moment value (symbol µ). The Cl atom obtains a partial negative (δ-) charge while the C atom attains a partial positive (δ+) charge.
The highly electronegative halogen atom not only attracts the shared electron cloud of the C-Cl bond but also attracts C-H electrons. The electron cloud stays non-uniformly distributed in the molecule overall. In conclusion, CH3Cl is a polar molecule (net µ = 1.86 D).
How many bond pairs and lone pairs are there in the Lewis dot structure of CH3Cl?
The CH3Cl Lewis structure displays a total of 14 valence electrons i.e., 14/2 = 7 electron pairs.
Out of the 7 electron pairs, there are 4 bond pairs and 3 lone pairs.
All the 3 lone pairs are present on the outer Cl atom while there is no lone pair of electrons on the central C atom or any one H-atom in CH3
What is the molecular shape of CH3Cl?
Chloromethane (CH3Cl) has a tetrahedral shape and molecular geometry. There is no lone pair of electrons on the central C-atom in CH3Cl thus it has an AX4 generic formula.
As a result, the CH3Cl molecule possesses an identical electron and molecular geometry.
What are the shapes of SiF4, PCl3, H2S, and CH3Cl?
The silicon tetrafluoride (SiF4) molecule has a tetrahedral shape. There are a total of 4 electron density regions around the central Si atom in SiF4 and there is no lone pair present on this central atom.
The PCl3 molecule has a trigonal pyramidal shape. There are a total of 4 electron density regions around the central P atom, out of which there is 1 lone pair. Lone pair-bond pair repulsions distort the shape of the molecule.
Dihydrogen sulfide (H2S) has a bent shape owing to the presence of 2 lone pairs of electrons on the central S-atom in H2 In addition to lone pair-bond pair repulsions, a lone pair-lone pair repulsive effect is also present in this molecule.
Chloromethane (CH3Cl) has a tetrahedral shape just like SiF4 as all the four electron density regions are constituted of bond pairs and there is no lone pair of electrons on the central C-atom.
Compare the shape and molecular geometry of CH3Cl with other haloalkanes such as CH2Cl2 and CHCl3.
In each of chloromethane (CH3Cl), dichloromethane (CH2Cl2), and trichloromethane or chloroform (CHCl3), a carbon (C) atom is present at the center.
There are a total of 4 electron density regions around the central C-atom so the ideal electronic geometry of each haloalkane is tetrahedral.
Also, there is no lone pair of electrons on the central C-atom in each of CH3Cl, CH2Cl2, and CHCl3 thus the molecular geometry or shape of each is the same as the electron geometry i.e., tetrahedral.
The total number of valence electrons available for drawing chloromethane or methyl chloride (CH3Cl) Lewis structure is 14.
CH3Cl has an identical electron and molecular geometry or shape i.e., tetrahedral.
The CH3Cl molecule has sp3 hybridization.
The bonded atoms form a mutual bond angle of 109.5° in the tetrahedral CH3Cl molecule.
The C-H bond is stronger and has a bond length of 107 pm while the C-Cl bond length is 134 pm in CH3Cl.
The CH3Cl molecule is overall polar (net µ > 0) due to the high electronegativity of the chlorine atom which attracts each C-H electron cloud in addition to attracting the C-Cl bonded electrons.
Zero formal charges present on all the bonded atoms in the CH3Cl molecule account for the extraordinary stability of the Lewis structure drawn in this article.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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