The electronegativity difference between two bonded atoms governs the polarity of a chemical covalent bond.
In this article, we will discuss whether the C-H bond is polar or non-polar, a question that often confuses many chemistry students.So let’s begin!
Is C-H bond polar or non-polar?
The C-H bond is non-polar, as per Pauling’s electronegativity scale.
However, as it comprises two dissimilar atoms i.e., a carbon (C) atom and a hydrogen (H) atom, therefore it has a weakly polar character present in it, which is often ignored.
Non-polar C-H bond as per Pauling’s electronegativity scale
Electronegativity is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
In the Periodic Table of elements, electronegativity increases across a period while it decreases down the group.
Specific electronegativity values are assigned to all the elements in the Periodic Table. Fluorine (F) is the most electronegative element, with an electronegativity value of 3.98. All the other elements possess electronegativity values lower than 3.98.
As per Linus Pauling, a polar covalent bond is formed between two dissimilar atoms having an electronegativity difference ranging from 0.4 to 1.6 units.
If the electronegativity difference between the concerning atoms is lower than 0.4 units, then it is considered non-polar.
If the difference is greater than 1.6 units, the chemical bond transforms its nature from covalent to ionic.
Within 0.4 to 1.6 units, the more electronegative atom (Y) strongly attracts the X-Y shared electron cloud towards itself; it thus gains a partial negative charge (δ–), having a slight excess of electrons.
In contrast, the less electronegative atom (X) develops a partial positive charge (δ+) owing to a slight electron deficiency.
In the C-H bond, the electronegativity value of carbon is 2.55, while that of hydrogen is 2.20. Therefore, there exists an electronegativity difference of 2.55-2.20 = 0.35 units between the bonded atoms in a C-H bond.
As 0.35 < 0.4; thus, the C-H bond is typically non-polar as per Pauling’s electronegativity scale.
However, sometimes chemistry differs in practice and experiment from what is its theoretical explanation.
Let’s explore this concept further w.r.t the C-H bond in the next section of the article.
Weakly polar character in a typically non-polar C-H bond
An ideal non-polar bond is formed between two identical atoms that have a zero electronegativity difference between them.
For instance, a C-C bond or an H-H bond is purely non-polar.
In a C-C bond, both carbon atoms possess an identical electronegativity value (2.55); therefore, both atoms attract the C-C shared electron cloud to the same extent.
Due to zero electronegativity difference, the charged electron cloud stays equally shared between two identical atoms.
As a C-H bond is composed of two dissimilar atoms which possess a certain electronegativity difference (although it is very small), the C-atom attracts the C-H electrons slightly more than the H-atom.
The C-atom thus gains a slight negative charge (Cδ–), while the H-atom obtains a slight positive charge (Hδ+) in the C-H bond.
Consequently, in the practical world, the C-H bond possesses a specific dipole moment value (symbol µ). The C-H dipole moment points from Hδ+ to Cδ–, as shown below.
However, it is experimentally proven that this C-H dipole moment has a very small value; therefore, it is often neglected, and the C-H bond is considered non-polar to make a chemistry student’s life easier.
In short, whenever a chemical covalent bond is formed between two dissimilar atoms, it always has some polar character and thus possesses a specific dipole moment value.
The dipole moment is a vector quantity defined as a product of charge (Q) and charge separation (r).
It depends on the magnitude of the dipole moment whether the polar character in a bond is significant or insignificant such as that in the C-H bond.
In conclusion, we agree with Pauling and say that the C-H bond is overall non-polar.
Non-polar, as well as polar molecules, can be formed, possessing one or more C-H bonds. It depends on the different types of bonds and the overall shape of the molecule, whether a C-H-containing covalent molecule is polar or non-polar overall.
Let’s see some examples.
Examples of non-polar molecules containing C-H bonds
Methane (CH4)
CH4 is the simplest hydrocarbon. It comprises four C-H bonds and a tetrahedral shape and geometry.
The small dipole moments of the C-H bonds get uniformly canceled in the symmetrical tetrahedral shape of CH4. So, it is overall non-polar (Net µ = 0).
Acetylene (C2H2)
C2H2 is made up of one C-C triple bond and two C-H bonds. The C-C bond is purely non-covalent as it is formed between two identical carbon atoms.
CH2Cl2 possesses two C-H bonds and two C-Cl bonds.
In the tetrahedral shape of the molecule, the highly electronegative Cl-atoms not only attract the C-Cl bonded electrons but also attract the shared electron cloud of each C-H bond.
The charged electron cloud stays non-uniformly distributed overall in the molecule.
Methanol or methyl alcohol (CH3OH) is made up of three C-H bonds, one C-O bond, and an O-H bond. The molecule possesses a tetrahedral shape w.r.t C-atom while a bent shape w.r.t O-atom.
The C-H bonds are almost non-polar, while the O-H bond is strongly polar. Oxygen being a highly electronegative element strongly attracts each of the three C-H bonded electrons in addition to attracting O-H electrons.
δ++ charges appear on the C-H bonded H-atoms, while the C-atom carries a δ+ charge.
The C-H bond is non-polar. As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms that have an electronegativity difference greater than at least 0.4 units.
As only an electronegativity difference of 0.35 units exists between a C and an H-atom in the C-H bond, thus, the C-H bond is considered very weakly polar, almost non-polar.
What does the electronegativity of an atom indicate?
Electronegativity is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
The higher the electronegativity of an elemental atom, the greater its ability to attract electrons from a bond pair.
Which is the most electronegative element of the Periodic Table?
Fluorine (F) is the most electronegative element of the Periodic Table.
It has an electronegativity value of 3.98 units.
Which is the least electronegative element in the Periodic Table?
Cesium (Cs) is the least electronegative element in the Periodic Table.
It has an electronegativity value of 0.79 units.
Which bond is polar as per Pauling’s electronegativity scale?
As per Pauling’s electronegativity scale, a covalent chemical bond is polar if the bonded atoms have an electronegativity difference between 0.4 to 1.6 units.
What type of bond is formed between two atoms if the difference in electronegativity is small, medium, or large?
A non-polar covalent bond is formed if the electronegativity difference between the bonded atoms is small (less than 0.4 units), such as the C-H bond.
A polar covalent bond is formed if the bonded atoms have an electronegativity difference between 0.4 to 1.6 units (medium), such as the C-Cl bond.
An ionic bond is formed between two atoms having large (greater than 1.6units) electronegativity differences, such as the Na-Cl bond.
Is the H-C bond polar?
No, the H-C bond is typically non-polar as it possesses an electronegativity difference of only 0.35 units between the bonded atoms i.e., hydrogen (E.N = 2.20) and carbon (E.N = 2.55).
Which of the following bonds is polar?
a) C-H
b) H-H
c) O-H
a) The C-H bond is considered non-polar as there is an electronegativity difference of only 0.35 units between the bonded atoms which is less than that required for a covalent bond to be polar as per Pauling’s electronegativity scale.
b) The H-H bond is non-polar as it is formed between two identical hydrogen atoms that have the same electronegativity value.
c) The O-H bond is strongly polar as it is made up of oxygen and a hydrogen atom possessing an electronegativity difference of 1.24 units.
Thus, out of all the above three, only the O-H bond is polar.
Summary
The C-H bond is non-polar as per Pauling’s electronegativity scale.
The covalently bonded carbon and hydrogen atoms possess an electronegativity difference of only 0.35 units.
As 0.35 <4 units. Thus, the C-H or H-C bond is typically non-polar.
A weakly polar character is present in the C-H bond as it is formed between two dissimilar atoms. It thus possesses a small dipole moment value, but as this dipole moment is very small so it can be easily ignored.
The polarity of a molecule containing a C-H bond depends on the other atoms and bonds present as well as on the overall molecular shape.
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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