Methylamine (CH3NH2) Lewis structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar or nonpolar
CH3NH2 is the chemical formula for methylamine, also known as methanamine or aminomethane. It is a colorless gas with a pungent fishy odor. It is an important chemical reagent in the pharmaceutical industry. It is also used as a pesticide, a paint remover, and a surfactant.
This article discusses how to draw the Lewis dot structure of CH3NH2, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polarity, etc.
So if you are interested to know all that and much more, then continue reading. Happy learning!
Name of Molecule
Methylamine
Chemical formula
CH3NH2
Molecular geometry of CH3NH2
Tetrahedral (w.r.t C-atom) and trigonal pyramidal (w.r.t N-atom)
How to draw lewis structure of CH3NH2 (Methlyamine)?
The Lewis structure of methylamine (CH3NH2) consists of a carbon (C) atom at the center. It is bonded to three H-atoms and an amine (NH2) functional group. In this way, the central C-atom is composed of a total of 4 electron density regions or electron domains.
All 4 electron density regions are constituted of bond pairs; thus, there is no lone pair of electrons on the central C-atom in the CH3NH2 Lewis structure.
Drawing the Lewis dot structure of CH3NH2 is not difficult at all, especially if you follow the simple steps given below.
Steps for drawing the Lewis dot structure of CH3NH2
1. Count the total valence electrons in CH3NH2
The very first step while drawing the Lewis structure of CH3NH2 is to calculate the total valence electrons present in its concerned elemental atoms.
As three different elemental atoms are present in CH3NH2, so you first need to look for the position of these elements in the Periodic Table.
Carbon (C) belongs to Group IV A (or 14), so it has a total of 4 valence electrons. Nitrogen (N) is present in Group V A (or 15), so it has 5 valence electrons, while hydrogen (H) lies at the top of the Periodic Table containing a single valence electron only.
∴ The CH3NH2 molecule consists of 1 C-atom, 1 N-atom, and 5 H-atoms. Therefore, the total valence electrons available for drawing the Lewis dot structure of CH3NH2 = 1(4) + 1(5) + 5(1) = 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.
Nitrogen (E.N = 3.04) is more electronegative than both carbon and hydrogen. Hydrogen (E.N = 2.20) is less electronegative than carbon (E.N = 2.55). Still, it cannot be chosen as the central atom because a hydrogen (H) atom can accommodate only 2 electrons which denotes 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.
Consequently, the C-atom is placed at the center of the CH3NH2 Lewis structure, while the N-atom and five H-atoms occupy terminal positions, as shown below.
3. Connect outer atoms with the central atom
In this step, the outer N-atom is joined to the central C-atom using a single straight line.
The 3 H-atoms lying next to the central C-atom are also joined to it directly by using single straight lines.
However, the two H-atoms lying next to the N-atom are not directly connected to the C-atom. This is because an H-atom can only form a single bond with its adjacent atom, as it can only accommodate a total of 2 valence electrons.
A nitrogen atom is highly electronegative, so it readily forms a covalent chemical bond with its adjacent H-atoms, not allowing the latter a chance to form a direct C-H bond.
A single straight line represents a bond pair containing 2 electrons. There are a total of 6 single bonds in the above structure representing 6(2) = 12 valence electrons.
∴ Hence, 12 valence electrons are already consumed out of the 14 initially available for drawing the CH3NH2 Lewis structure.
4. Complete the duplet and/or octet of the outer atoms
As we already identified, the hydrogen and nitrogen atoms are the outer atoms in the Lewis dot structure of CH3NH2.
Each hydrogen (H) atom requires a total of 2 valence electrons in order to achieve a stable duplet electronic configuration.
A C-H bond and an N-H single bond already represent 2 valence electrons around each H-atom. This means all five 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, an N-atom needs a total of 8 valence electrons to achieve a stable octet electronic configuration.
One N-C bond and two N-H bonds represent a total of 3(2) = 6 valence electrons around the nitrogen atom. This denotes that it has a deficiency of 2 more electrons in order to complete its octet.
∴ So 2 valence electrons are placed as a lone pair on the N-atom in the CH3NH2.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 6 single bonds + electrons placed around the N-atom, shown as dots = 6(2) + 2 = 14 valence electrons.
Total valence electrons – electrons used till step 4 = 14 – 14 = 0 valence electrons.
As all the valence electrons initially available for drawing the CH3NH2 Lewis structure are already consumed hence there is no lone pair of electrons on the C-atom at the center.
The central C-atom already has 4 single bonds (3 C-H bonds + 1 C-N bond) around it. 4 single bonds mean 8 valence electrons, i.e., a complete octet of the central C-atom. So we need not make any further changes in the Lewis structure obtained below.
As a final step, we just need to check the stability of this Lewis structure. Let’s do that using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The fewer formal charges present on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
What are the electron and molecular geometry of CH3NH2?
With respect to the central C-atom, the molecular geometry or shape of CH3NH2 is identical to its ideal electron pair geometry, i.e., tetrahedral. With respect to the N-atom, the molecular geometry or shape of CH3NH2 is trigonal pyramidal.
There is no lone pair of electrons on the central C-atom in CH3NH2; therefore, there is no distortion in the shape and geometry of the molecule.
However, there is a lone pair of electrons on the N-atom that leads to lone pair-bond pair electronic repulsions; thus, the molecule occupies a trigonal pyramidal shape with respect to the N-atom.
Molecular geometry of CH3NH2
The methylamine (CH3NH2) molecule has a tetrahedral shape with respect to the C-atom.
As there is no lone pair of electrons on the central carbon atom in CH3NH2, so no lone pair-lone pair or lone pair-bond pair repulsions exist in the molecule with respect to the C-atom. A bond pair-bond pair repulsive effect does exist.
To minimize the bond pair repulsions, the bonded atoms arrange around the central C-atom as four vertices of a regular tetrahedron, as shown below.
An interesting fact is that if you consider the shape of CH3NH2with respect to the N-atom, then three different atoms are directly bonded to the N-atom, and it has a lone pair of electrons. Lone pair-bond pair repulsions tilt the CH3 group and H-atoms such that the molecule occupies a trigonal pyramidal shape, as shown below.
As we considered the less electronegative C-atom as the only central atom while drawing the Lewis structure of the molecule. Therefore, the tetrahedral molecular shape and geometry of CH3NH2 hold greater significance.
Electron geometry of CH3NH2
According to the valence shell electron pair repulsion (VSEPR) concept of chemical bonding, the ideal electronic geometry of a molecule containing 4 regions of electron density around the central atom is tetrahedral.
The central C-atom has three H-atoms and one NH2 group in CH3NH2. This makes a total of 4 electron density regions or electron domains around the central C-atom. Thus its ideal electron pair geometry is tetrahedral.
To be sure, the ideal electron geometry of CH3NH2with respect to the N-atom is also tetrahedral because one CH3 group, 2 H-atoms, and 1 lone pair make a total of 4 electron density regions around the N-atom as well.
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 shape and geometry of a molecule based on the VSEPR concept.
AXN notation for CH3NH2 molecule
A in the AXN formula represents the central atom. In CH3NH2, a carbon (C) atom is present at the center, so A = C.
X denotes the atoms bonded to the central atom. In CH3NH2, three hydrogens (H) atoms and an amine (NH2) group are directly bonded to the central C-atom. The NH2 group is considered 1 region of electron density. In short, X = 3+1 = 4 for CH3NH2.
N stands for the lone pairs present on the central atom. As per the Lewis structure of CH3NH2, there are no lone pairs of electrons on the central carbon; hence N = 0.
As a result, the AXN generic formula for CH3NH2 is AX4.
Now, you may have a quick 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 ideal electron pair geometry, i.e., tetrahedral, as we already noted down for methylamine (CH3NH2).
Hybridization of CH3NH2
Both C and N-atoms have sp3 hybridization in CH3NH2.
The electronic configuration of carbon is 1s2 2s2 2p2.
During chemical bonding, the 2s atomic orbital of carbon hybridizes with its three 2p atomic orbitals to produce 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.
An sp3 hybrid orbital of carbon overlaps with the sp3 hybrid orbital of nitrogen to form the C-N sigma (σ) bond by sp3-sp3 overlap.
The other three sp3 hybrid orbitals overlap with the s-orbitals of adjacent hydrogen atoms to form the C-H sigma bonds by sp3-s overlap.
CH3NH2 hybridization can also be determined from its steric number. The steric number of the central C-atom in CH3NH2 is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The CH3NH2 bond angle
Due to the different types of bonds present in CH3NH2, it consists of multiple bond angles. In ascending order, the H-N-H bond angle is 106°, the H-C-H bond angle is 108°, the C-N-H bond angle is 109°, and the H-C-N bond angle is 112°.
Similarly, different lengths are present in the CH3NH2 molecule, as shown below.
Pauling’s electronegativity scale states that a covalent chemical bond is polar if an electronegativity difference of 0.5 to 1.6 units exists between the bonded atoms.
A small electronegativity difference of 0.35 units exists between the carbon and hydrogen atoms in each C-H bond. However, nitrogen is a highly electronegative element.
So, an electronegativity difference of 0.49 units exists between a carbon (E.N = 2.55) and a nitrogen (E.N = 3.04) atom.
Thus the central C-N bond is polar in the CH3NH2 molecule. An even higher electronegativity difference of 0.84 units is present between a nitrogen and a hydrogen (E.N = 2.20) atom. Thus both N-H bonds are also polar.
Nitrogen strongly attracts the shared electron cloud from each of the C-N and N-H bonds. Nitrogen gains a partial negative (δ–) charge while each of C and H-atoms attains partial positive (δ+) charges.
The electron cloud stays non-uniformly distributed over the molecule. Thus CH3NH2 is overall polar (net µ = 1.31 D).
The Lewis structure of CH3NH2 displays a total of 14 valence electrons i.e., 14/2 = 7 electron pairs.
Out of the 7 electron pairs, there are 6 bond pairs and 1 lone pair.
The 6 bond pairs are composed of 1 C-N bond, 3 C-H bonds and 2 N-H bonds.
1 lone pair of electrons is present on the nitrogen atom.
There is no lone pair on either of the C or H-atoms in the CH3NH2 Lewis structure.
What is the molecular shape of CH3NH2 with respect to the C-atom?
The molecular geometry or shape of CH3NH2 is tetrahedral with respect to the central C-atom. 4 different atoms are bonded to the central C-atom, and there is no lone pair of electrons present on it.
Its AXN generic formula with respect to C-atom is AX4.
What is the molecular shape of CH3NH2 with respect to the N-atom?
The molecular geometry or shape of CH3NH2 with respect to the N-atom is trigonal pyramidal. 3 different atoms are directly bonded to the N-atom, and it has a lone pair of electrons.
The lone pair of electrons leads to lone pair-bond pair repulsions; thus, the molecular shape gets distorted. Its AXN generic formula with respect to C-atom is AX3N.
What is the electron geometry of CH3NH2?
The ideal electronic geometry of CH3NH2 is tetrahedral. There are three C-H bonds and one C-N bond around the central C-atom in CH3NH2.
This makes a total of 4 electron density regions around the carbon atom hence tetrahedral electron geometry.
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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