Is CH3NH2 polar or non-polar? - Polarity of CH3NH2

CH₃NH₂ is the chemical formula of an organic compound, a derivative of ammonia known as methylamine. It is a colorless gas with a pungent fishy odor resembling the odor of ammonia.

CH₃NH₂ has a molar mass of 31.05 g/mol. It is used in making pharmaceuticals, insecticides, paint removers, surfactants, and rubber chemicals.  

So are you excited to find out whether the methylamine CH₃NH₂ molecule is polar or non-polar? If yes, then continue reading this article.  

Is CH₃NH₂ polar or non-polar?

Methylamine (CH₃NH₂) is a polar molecule. It consists of one carbon (C) atom, one nitrogen (N) atom, and five hydrogens (H) atoms. The carbon and nitrogen atoms are kept at the central position making a C-N bond. The hydrogen atoms are at the surrounding positions.

The carbon atom is surrounded by three H-atoms, while the nitrogen atom is surrounded by two H-atoms. The molecular geometry of CH₃NH₂, with respect to C-atom, is tetrahedral, while with respect to N-atom, it is trigonal pyramidal.

Between bonded atoms, an electronegativity difference of 0.49 units exists in the C-N bond, 0.35 units exist in C-H bonds, and 0.84 units exist between atoms in the N-H bonds.

Thus, C-N, C-H, and N-H bonds are individually polar in the CH₃NH₂ molecule and possess a specific dipole moment value (symbol µ). 

In CH₃NH₂, the nitrogen atom contains one lone pair of electrons and also is strongly electronegative, so it attracts electrons from each of the C-N and N-H bonds to a large extent.

The electron cloud in CH₃NH₂ does not stay uniformly distributed in the molecule overall due to its asymmetric shape. As a result, the CH₃NH₂ molecule is overall polar (net µ= 1.31 Debye). 

What makes a molecule polar or non-polar?

A molecule is polar if there is a non-uniform charge distribution present in it. If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.

The following three factors mainly influence the polarity of a molecule:

• The electronegativity difference between two or more covalently bonded atoms
• Dipole moment
• Molecular geometry or shape

Now, let us discuss the effect of the above three factors one by one to prove that the methylamine (CH₃NH₂) molecule is overall a polar molecule.

Factors affecting the polarity of CH₃NH₂

Electronegativity

It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.

Electronegativity increases across a period in the Periodic Table while it decreases down the group.

Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.

Carbon (C) is present in Group IV A of the Periodic Table. The electronic configuration of carbon is 1s² 2s² 2p². As per this electronic configuration, a C-atom has a total of 4 valence electrons. It is thus short of 4 more electrons that are required so that the carbon atom can achieve a complete octet electronic configuration.

Hydrogen (H) is present in Group IA of the Periodic Table. The electronic configuration of hydrogen is 1s¹. According to this electronic configuration, an H-atom has 1 electron in its only shell, thus lacking one more electron to complete its duplet.  

Conversely, Nitrogen (N) is present in Group VA of the Periodic Table. The electronic configuration of nitrogen is 1s² 2s² 2p³ which translates as a total of 5 valence electrons. It has a deficiency of three electrons to complete its stable octet configuration.

In this way, the central C-atom and the N-atom attain a complete octet, while each of the five H-atoms obtains complete duplet electronic configuration via chemical bonding in the methylamine Lewis structure shown above. 

All the valence electrons of carbon atom get consumed in the bond formation, so it has no lone pair, but there is one lone pair of electrons on the central N-atom in CH₃NH₂. Hence, there is distortion in the shape or geometry of the molecule w.r.t N-atom.

CH₃NH₂ contains a C-atom (E. N= 2.55), an N-atom (E. N= 3.04), and H-atoms (E. N= 2.20). Hence, between bonded atoms, the electronegativity difference in the C-N bond is 0.49 units, in each C-H bond is 0.35 units, and in each N-H bond is 0.84 units, respectively.

The more electronegative N-atom (E. N= 3.04), along with having a lone pair of electrons, not only strongly attracts the shared electron cloud away from the central C-atom in the C-N bond but also attracts C-H bonded electrons in the CH₃NH₂ molecule.

Thus, the nitrogen atom present in CH₃NH₂ gains a partial negative (N^δ-) charge, while the central carbon atom obtains a partial positive (C^δ+) charge. All hydrogen atoms also gain partial positive (H^δ+) charges, as shown below.

As a result, with specific electronegativity differences, all of the N-H, C-H, and C-N bonds are individually polar in CH₃NH₂ (as shown below).

Dipole Moment

Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.

It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).

The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.

So in CH₃NH₂, the dipole moment of polar C-N bond points from C^δ+ to N^δ-. The dipole moment of N-H bonds also points from H^δ+ to N^δ-.

Nitrogen being strongly electronegative, not only attracts C-N and N-H bonded electrons but also attracts C-H electrons; thus, the H-atoms bonded to the C-atom gains H^δ++ charges, indicating an extreme electron deficiency. The dipole moments of weakly polar C-H bonds thus point from H^δ++ to C^δ+.

Molecular geometry

The CH₃NH₂ molecule adopts two different shapes according to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding. It is an AX₄-type molecule as per the least electronegative C-atom. However, considering the more electronegative nitrogen (N) atom as the central atom, CH₃NH₂ is an AX₃E₁-type molecule.

To one C-atom at the center (A), four bonded atoms (X) are attached (three H-atoms and one N-atom), and the central C-atom contains no lone pair of electrons (E). So, w.r.t C-atom, the molecular geometry or shape of CH₃NH₂ is identical to its ideal electron pair geometry, i.e., tetrahedral.

In contrast, to one N-atom at the center (A), three bonded atoms (X) are attached (two H-atoms and one C-atom), and the central N-atom contains one lone pair of electrons (E). Hence the molecular geometry or shape of CH₃NH₂ w.r.t N-atom is trigonal pyramidal.

To minimize electronic repulsions and to attain stability, the bonded atoms of the CH₃NH₂ molecule possess bond angles of ∠ (H-N-H) = 106°, ∠ (H-C-H) = 108°, ∠ (C-N-H) = 109°, and ∠ (H-C-N) = 112°.

In conclusion, it is due to the asymmetric trigonal pyramidal shape of CH₃NH₂ w.r.t N-atom that the dipole moments of individually polar C-N, N-H, and C-H bonds do not get canceled overall in the molecule.

Nitrogen being strongly electronegative, not only strongly attracts the shared electron cloud from each of the C-N and the N-H bonds but also attracts C-H bonded electrons. This leads to a non-uniform charge distribution in the molecule.

Consequently, methylamine (CH₃NH₂) is overall a polar molecule (net µ = 1.31 D). 

Difference between polar and nonpolar?

Also, check –

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FAQ

Summary

• Methylamine (CH₃NH₂) is a polar molecule.
• It consists of one C-N bond, three C-H, and two N-H bonds with specific electronegativity differences of 0.49, 0.35, and 0.84 units, respectively.
• C-N and N-H bonds are strongly polar, while the C-H bonds are only weakly polar.
• Methylamine CH₃NH₂, with respect to the central C-atom, has a tetrahedral molecular shape, while with respect to N-atom, it has a trigonal pyramidal molecular shape and geometry.
• Due to the presence of one lone pair of electrons on the N-atom and the asymmetric trigonal pyramidal shape of the molecule w.r.t this atom, the individual dipole moments do not get canceled, and the electron cloud stays non-uniformly spread over the molecule.
• The net dipole moment in CH₃NH₂ is µ = 1.31 Debye, so it is overall a polar molecule.