Polarity is the distribution of electric charges over atoms joined by a bond. These atoms have different electronegativity values and the difference between these values accounts for the polarity of the bond.
A general rule states that an electronegativity difference less than 0.4 means the bond is non-polar and an electronegativity difference greater than 0.4 signifies a polar bond. Methane, CH4, is a simple compound that contains two atoms with close electronegativity values.
Beyond being an organic compound and its unique properties, the polarity of CH4 is worth studying. polarity depends on electronegativity, but it may also be influenced by molecular geometry and hybridization. All these are discussed in this article.
Properties of CH4
- Methane, CH4, is the simplest and first of the alkane series
- It is a saturated hydrocarbon with one carbon atom and four hydrogen atoms
- It is a non-toxic, colorless, and odorless gas that is lighter than air. Methane has a specific gravity of 0.554, a density of 0.656 Kg/m3
- CH4 has a molar mass of 16.04 g/mol, a melting point of – 296.5°F (- 182.5°C), and a boiling point of – 258.7°F (-161.5°C)
- Methane is highly flammable and produces a lot of heat. It burns in the air with a blue flame and produces heat on combustion
- Also, this gas is almost insoluble in water (with a solubility value of 22.7 mg/L). However, it is soluble in ethanol, methanol, benzene, diethyl ether, and toluene
- Furthermore, methane is one of the most important greenhouse gases. It is also a useful fossil fuel and bacterial metabolite
What is the polarity of CH4?
CH4 lacks polarity; it is non-polar. There are explanations for this.
Electronegativity
The constituent elements in CH4 are carbon and hydrogen. These elements have very similar electronegativities. Carbon has an electronegativity of 2.55 and hydrogen has a value of 2.20. the electronegativity difference is 0.35.
The general rule for determining polarity through electronegativity states that an electronegativity difference of less than 0.5 signifies a non-polar bond, while a difference of greater than 0.5 signifies a polar bond.
Due to the large electronegativity difference between polar molecules, charges are unevenly distributed over the atoms. On the other hand, electrons are shared equally in non-polar molecules because of the small electronegativity difference.
Arrangement of atoms
Carbon is more electronegative than hydrogen, so it pulls the shared electrons more to itself. As a result, the carbon atom acquires a partial negative charge, and the hydrogen atoms acquire partial positive charges.
This results in an uneven distribution of charges between the atoms. The resulting C-H bonds are polar and generate dipole moments.
However, because of the symmetrical arrangement of the hydrogen atoms around the central carbon atom, the individual dipole moments cancel out each other. The overall molecule has a zero net dipole moment of zero and is non-polar.
How does molecular geometry determine the polarity of CH4?
CH4 has a tetrahedral geometry due to the arrangement of the four hydrogen atoms that surround the central carbon atom. All four C-H bonds are equal and have a bond length of 109 pm.
The CH4 molecule has no lone pair of electrons that distort its shape, so it has the ideal bent shape of a tetrahedral molecule with an H-C-H bond angle of 109.5°.
As mentioned earlier, the molecule has a symmetrical shape because of its tetrahedral geometry. In symmetrical molecules, dipole moments cancel out each other and result in a non-polar molecule.
What factors can affect the polarity of CH4?
The lack of polarity of CH4 is due to the following:
- The electronegativity difference between the carbon and hydrogen atoms
- The hybridization of the carbon atom
- The molecular geometry and symmetrical arrangement of the hydrogen atoms
- Absence of dipole moments
- Interaction with solvents due to the weak intermolecular attractions between the molecules
Does the non-polar nature of CH4 affect its physical and chemical properties?
Yes, it does. The lack of polarity of CH4 affects its solubility. It is more soluble in non-polar solvents and insoluble in polar solvents. It also influences its rate of combustion. Methane gas is commonly used as a fuel for burning in the air.
Also, methane has low boiling and melting points because of its lack of polarity. Polar molecules, on the other hand, have higher boiling and melting points.
Additionally, because of its lack of polarity, this gas has weaker intermolecular forces such as the London dispersion force unlike the stronger dipole-dipole forces present in polar molecules.
The weak intermolecular attractions in methane also account for its low boiling point and gaseous state.
Does CH4 have dipole-dipole forces?
CH4 does not have dipole-dipole forces because it has a net dipole moment of zero.
Methane has other intermolecular forces called London force or dispersion force due to the temporary development of polarity, despite being a non-polar molecule.
What is the hybridization of CH4?
CH4 has an sp3 hybridisation. The hybridization of the molecule comes from the hybridization of the central carbon atom. In the valence shell of the carbon atom, one 2s orbital and three 2p orbitals mix to form four sp3 orbitals.
The four hydrogen atoms use these four hybrid sp3 orbitals to form C-H sigma bonds. The four sp3 hybrid orbitals are of equal energy and shape and they have one unpaired electron each. The hybridization of methane explains its molecular geometry and bond angles.
The hybrid orbitals are arranged in such a way that the bond pair-bond pair repulsion between them is minimal. The slight repulsion makes it form a tetrahedron with a bond angle of 109.5°.
FAQs
Does CH4 obey the octet rule?
Methane obeys the octet rule. The four hydrogen atoms share covalent bonds with the central carbon atom. One covalent bond contains two electrons that come from the
What is the electron pair geometry of CH4?
There are four electron pairs in the four C-H distributed in a tetrahedral shape. Therefore, the electron pair geometry of CH4 is tetrahedral.
Does CH4 have resonance structures?
Methane cannot have resonance structures because the hydrogen atoms bonded to the central carbon atom are similar. As a result, there are no Lewis dot structures and no resonance.
What is the charge of CH4?
CH4 has an overall charge of 0. The formal charge of each atom in methane is 0 and they all sum up to 0, its overall charge.
Conclusion
Carbon and hydrogen are almost similar atoms as they have near electronegativities. The difference between them is small makes CH4 a non-polar molecule. Also, the arrangement of the four hydrogen atoms around carbon gives it its tetrahedral geometry, explaining its non-polar nature.
The individual C-H bonds generate dipole moments which cancel due to their symmetrical arrangement. This results in the overall zero net dipole moment and its lack of polarity. The physical and chemical properties of CH4 are impacts of its non-polar nature.
Also, learn about the polarity of methanol, CH3OH, the first in the alcohol series.
Thanks for reading.