Is CH3Br polar or nonpolar? - Polarity of CH3Br
Methyl bromide is an important colorless, odorless and non-flammable hydrofluorocarbon. The chemical formula CH3Br represents this ozone-depleting gas. The IUPAC name of CH3Br is bromomethane.
CH3Br is extensively used as a fumigant insecticide and has a potential role as a fire-extinguishing agent. It is a highly toxic chemical, and prolonged exposure can even be fatal.
So what is the polarity of this highly toxic gas bromomethane (CH3Br)? Is it a polar or a non-polar molecule? Let’s find out in this article.
Is CH3Br polar or non-polar?
Methyl bromide (CH3Br) is a polar molecule. The central carbon (C) atom in the CH3Br molecule is surrounded by three hydrogens (H) and one bromine (Br) atom via single covalent bonds, forming a tetrahedral molecule.
The electronegativity of the bromine (Br) atom is greater than the carbon (C) and hydrogen (H) atoms. The higher electronegative Br atom attracts the shared electron clouds with more influence in the CH3Br molecule.
Thus, all the bonds are individually polar and possess a specific dipole moment value.
The asymmetric arrangement of atoms in the tetrahedral-shaped CH3Br molecule further enhances the polarity effect as the dipole moments of the bonds is not canceled in the molecule overall. Thus, CH3Br is a polar molecule with a net dipole moment value > 0.
|Name of molecule||Methyl bromide (CH3Br)|
|Bond type||Polar covalent|
|Polar or Non-polar?||Polar|
|Dipole moment||1.83 D|
|Bond angle||112.5° and 107.7°|
What is a polar and non-polar molecule?
In chemistry, a molecule with unequal charge distribution between different centers of bonded atoms is a polar molecule.
It is formed by the covalent bond between two different atoms leading to an asymmetric electron density.
In this case, the atoms acquire partial positive (δ+) and partial negative (δ–) charges.
If the dipole moments of individually polar bonds are not cancelled due to the asymmetrical shape of the molecule, the molecule will be polar, such as CH3Br.
Hence a polar molecule has an unequal distribution of the electronic charge. Contrarily, if the electronic charge is evenly distributed over the molecule, in that case, it will be a non-polar molecule overall.
The following three factors influence the polarity of any covalent molecule:
- Dipole moment.
- Molecular geometry or shape.
In the next section, we will discuss how these factors control the polarity of the CH3Br molecule.
Factors affecting the polarity of CH3Br
It is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity decreases down the group in the Periodic Table of elements while it increases across a period.
Greater the electronegativity difference between the bonded atoms in a molecule, the higher the bond polarity.
Hydrogen belongs to group 1-A (or 1) of the Periodic Table. The electronic configuration of hydrogen is 1s1, so it has 1 valence electron.
Carbon belongs to group IV-A (or 14) of the Periodic Table. The electronic configuration of carbon is 1s2 2s2 2p2, so it has 4 valence electrons available for bonding.
On the other hand, bromine belongs to group VII-A (or 17) of the Periodic Table. The electronic configuration of bromine is 1s22s22p63s23d104s24p5, indicating the presence of 7 valence electrons.
The three H-atoms and one Br-atom thus form a single covalent bond with the central C-atom on each side of the CH3Br molecule.
|Atom||Electronic configuration||Valence electrons|
The electronegativity bromine atom is more electronegative than the carbon and hydrogen atoms (E.N of Br = 2.96, E.N of C = 2.55, E.N of H = 2.2).
Due to this electronegativity difference, the Br-atom strongly attracts the shared electron cloud from the bonds. The bonded electrons are held significantly close to the bromine atom in the CH3Br molecule.
The central C-atom and H-atoms thus gain a partial positive charge (Cδ+ and H δ+), while the bromine atom being more electronegative, obtains a partial negative (Brδ-) charge. In this way, oppositely charged poles develop in the CH3Br molecule.
The Br atoms not only attract the shared electron cloud of each C-Br bond but also attracts C-H electrons. As a result, the electron cloud distribution in the molecule is non-uniform overall. Thus, CH3Br is a polar molecule.
The dipole moment is the product of electrical charge (Q) and bond length (r) between two bonded atoms. It is a vector quantity expressed in Debye (D) units.
It is represented by a Greek symbol µ and measures the polarity of a bond.
The dipole moment of any molecule depends on the difference in electronegativity between the bonded atoms. The greater the electronegativity difference, the higher the bond polarity, resulting in a high dipole moment value.
It points from the partial positive (δ+) center to the partial negative (δ–) center of a bond or molecule.
The difference in electronegativity between the bonded atoms in the CH3Br molecule leads to dipoles pointing from Cδ+and Hδ+ to Brδ-.
Thus, each bond in the CH3Br molecule is polar, with a net dipole moment greater than 0.
As discussed earlier, a methyl bromide (CH3Br) molecule consists of three single C-H covalent bonds and one C-Br covalent bond. There are a total of 14 valence electrons in the overall molecule.
According to the Valence Shell Electron Pair Repulsion Theory (VSEPR) theory of chemical bonding, CH3Br is an AX4-type molecule. Around the central carbon atom (A) are four bond pairs of electrons (X).
To minimize the electronic repulsions between the atoms, the methyl bromide (CH3Br) molecule adopts a tetrahedral geometry with an H-C-H and H-C-Br bond angle of 112.5° and 107.7°, respectively.
As a result of the asymmetric arrangement of atoms around the central carbon, the individual dipole moments of the bonds do not get canceled in the methyl bromide (CH3Br) molecule. There is an unequal distribution of electronic charge over the molecule.
In conclusion, CH3Br is a polar molecule with a net dipole moment (µ = 1.83 D).
Difference between polar and nonpolar?
|Polar molecule||Non-polar molecule|
|Atoms must have a difference in|
|Atoms may have the same or different electronegativity values|
|Unequal charge distribution overall||Equal charge distribution overall|
|Net dipole moment greater than zero||Net dipole moment equals to zero|
|Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), methyl bromide/bromomethane (CH3Br), bromine pentafluoride (BrF5), etc.||Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), etc.|
Also, check –
- How to tell if a molecule is polar or nonpolar?
- Is CH3Cl polar or nonpolar?
- Is CH2Cl2 polar or nonpolar?
- Is CH2Br2 polar or nonpolar?
- Is CH3F polar or nonpolar?
- Is NCl3 polar or nonpolar?
- Is NO3– polar or nonpolar?
- Is BrF5 polar or nonpolar?
- Is SF4 polar or nonpolar?
- Is CO2 polar or nonpolar?
- Is NH3 polar or nonpolar?
- Is SO2 polar or nonpolar?
- Is SO3 polar or nonpolar?
- Is H2O polar or nonpolar?
- Is H2S polar or nonpolar?
- Is HCN polar or nonpolar?
- Is CCl4 polar or nonpolar?
- Is XeF4 polar or nonpolar?
- Is CH2O polar or nonpolar?
- Is CHCl3 polar or nonpolar?
- Is SF6 polar or nonpolar?
- Is BF3 polar or nonpolar?
- Is PCl5 polar or nonpolar?
Why is methyl bromide/bromomethane (CH3Br) polar?
Thus, CH3Br is a polar molecule.
The polarity of CH3Br is less than CH3Cl. Why?
The greater the electronegativity difference between the bonded atoms, the higher the bond polarity, resulting in a high dipole moment value.
Chlorine ( E.N = 3.16) is more electronegative than the bromine atom (E.N = 2.96).
Thus, the chlorine atom will attract the shared electron pairs in the CH3Cl molecule with more influence than the bromine atom in the CH3Br molecule.
As a result, the C-Cl bond will be more polar than the C-Br bond.
Thus, the polarity of CH3Br is less than CH3Cl.
Compare the polarity of CH3Br and CH3I molecules.
Greater the electronegativity difference between the bonded atoms in any molecule, the higher the bond polarity
Bromine ( E.N= 2.96) is more electronegative than the iodine atom (E.N = 2.66).
As a result, bromine will attract the shared electron clouds in the CH3Br molecule more than the iodine atom in the CH3I molecule.
Thus, the bond polarity of the C-Br bond will be greater than the C-I bond.
Thus, CH3Br is more polar than the CH3I molecule with a higher dipole moment value.
Is there a formal charge on the bonded atoms in the CH3Br molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
For hydrogen atoms
∴ The formal charge on the hydrogen atoms = 1-0-2/2 = 1-1 = 0
For bromine atom
∴ The formal charge on the bromine atom = 7-6-2/2 = 1-1 = 0
For carbon atom
∴ The formal charge on the central carbon atom = 4-0-8/2 = 4-4 = 0
Thus, no formal charge is present on the methyl bromide (CH3Br) molecule.
- Methyl bromide/bromomethane (CH3Br) is a polar molecule.
- Due to an electronegativity difference between the bonded bromine, hydrogen, and carbon, polar covalent bonds are generated.
- The bromine atom strongly attracts the shared electron cloud from the CH3Br molecule.
- The electronegativity difference between the bonded atoms leads to dipoles pointing from C δ+and Hδ+ to Brδ-.
- The AX4 type CH3Br molecule adopts a tetrahedral geometry.
- Due to the unsymmetrical arrangement of atoms in the tetrahedral molecule, the individual dipole moments of the bonds are not canceled in the molecule overall.
- Thus, CH3Br is a polar molecule (μ = 1.83 D).
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