Methane is a colorless and odorless gas with the chemical formula CH4 i.e. one atom of carbon is bonded to four other atoms of hydrogen. It belongs to group-14 hydride (chemical compounds consisting of hydrogen atoms and group 14 atoms).
Methane is the most basic alkane and the primary component of natural gas. It is produced by anaerobic bacteria which are found in landfills and the gut of ruminants.
It is one of the most significant greenhouse gases, with human activities accounting for about 70% of methane emissions. Pure methane is a high-energy feedstock with a 55.7 MJ/kg energy density that is used to produce electricity, heat homes, and for cooking.
In the year 1776, Alessandro Volta, an Italian physicist, was the first to scientifically recognize methane.
Most of the students wonder if methane is ionic or covalent. The presence of four hydrogen atoms makes it further confusing. In this blog, I will provide you clear answers to this question and discuss the concepts of bonding in detail.
So, is Methane (CH4) a covalent compound? Let’s find out in the next section.
A methane molecule is made up of four hydrogen atoms and one carbon atom. Hydrogen has an electronegativity of 2.2 and carbon has an electronegativity of 2.55.
An ionic compound is one in which the electronegativity difference between its constituent atoms is greater than 1.7. But as you can see, the electronegativity difference between carbon and hydrogen is 2.55-2.2 = 0.35 which is considerably smaller than 1.7. Since the electronegativity difference between them is very small, methane which has four C-H bonds is a covalent compound.
Since each hydrogen atom is one electron short of an octet configuration (complete shell) and carbon is four electrons short of a full outer shell of eight, four hydrogen atoms share electrons with the four outer electrons of carbon, resulting in full outer shells for all five atoms.
As hydrogen and carbon atoms exchange their outer electrons, hydrogen attains the electronic configuration of helium and carbon attains that of neon. As a result, while forming covalent bonds both the hydrogen and carbon atoms essentially have outer shells with 8 electrons.
Well, that was a crisp answer. Now let me discuss the covalent nature of methane in detail.
Before we dig into the details of covalent bonds in methane, let’s start from the basics. First, I will explain the concept of bonding and its types.
What is Chemical Bonding?
Chemical bonding is the development of a chemical compound by forming a chemical bond between two or more atoms, molecules, or ions. The atoms in the resulting compound are held together by chemical bonds.
Usually, the valence electrons are involved in chemical bonding though electrons from inner shells also participate in some cases. Valence electrons are the electrons present in the valence shell or the outermost shell of an atom.
Ever thought about the reason why all atoms participate in chemical bonding? I have the answer for you. Read on…
All the atoms prefer to stay in the ground state. This is the state with the least energy and highest stability. An atom is most stable when it attains octet configuration i.e. when its valence or outermost shell is completely filled with 8 electrons. All the atoms try to achieve the ground state by completing the octet.
To fill the outermost shell with eight electrons, atoms participate in chemical reactions. They try to attain this stable configuration by losing, gaining, or sharing electrons from one atom to another. Two atoms can combine to form either a molecule or a compound.
Now, let’s look into the types of chemical bonds.
Types of Chemical Bonds
Based on whether the atoms are transferred completely or shared the chemical bonds can be classified into the following:
- Ionic Bonds
- Covalent Bonds
When the valence (outermost) electrons of one atom are permanently transferred to another atom, an ionic bond is formed. These bonds are formed due to the electrostatic attraction between oppositely charged ions.
The atom that loses electrons becomes a positively charged ion (cation), while the atom that absorbs electrons becomes a negatively charged ion (anion).
Elements with extremely high ionization energies are unable to lose electrons, and those with extremely low electron affinity are unable to accept electrons.
Such elements’ atoms appear to share electrons with atoms of other elements or with atoms of the same element in such a way that both atoms achieve an octet arrangement in their respective valence shells.
Thus they achieve stability. In short, a covalent bond refers to an association formed by the sharing of electron pairs among different or similar kinds of molecules.
Covalent Bonding in Carbon Atom
To become stable, Carbon’s electronic configuration needs it to gain or lose four electrons, which seems unlikely because:
- Carbon cannot gain four electrons to become C4- because six protons cannot carry ten electrons, causing the atom to become unstable.
- Carbon cannot lose four electrons to become C4+ because doing so would take a lot of energy, and C4+ would only have two electrons retained by the proton, making it unstable once more.
Since carbon cannot accept or donate electrons, the only option left is sharing electrons to complete its nearest noble gas configuration and thereby form a covalent bond.
Covalent Bond Properties
If sharing a single electron pair between atoms does not satisfy octet configuration, the atoms can share more than one electron pair. Let’s see some properties of covalent bonds:
- They are extremely strong chemical bonds between atoms.
- A covalent bond usually contains about 80 kilocalories per mole (kcal/mol) of energy.
- Covalent bonds rarely break on their own after they have been established.
- The atoms that are bonded have unique orientations relative to one another, so covalent bonds are directional.
- The melting and boiling points of most covalently bound compounds are relatively low.
- The enthalpies of vaporization and fusion are normally lower in compounds with covalent bonds.
- Since there are no free electrons in covalently bonded compounds, they do not conduct electricity.
- Covalent compounds are insoluble in water.
It is an atom’s property that causes it to draw the mutual electron pair towards it. The Pauling scale is used to calculate the electronegativity of the atoms.
Ionic bonds are described as chemical bonds in which the electronegativity difference between two atoms in a chemical bond is greater than 2.0. If the difference is less than 2.0 on the Pauling scale, a covalent bond is present.
Why is CH4 a covalent compound?
In the case of methane (CH4),
The electronegativity value of the hydrogen atom = 2.20
The electronegativity value of the carbon atom = 2.55
The electronegativity difference of the H-C bond = 2.55 – 2.20 = 0.35
Since the electronegativity difference is only 0.35 on Pauling Scale, all the C and H atoms in methane are covalently bonded making it a covalent compound.
Properties of Methane
- Boiling Point: -161.6 0C
- Melting Point: -182.6 0C
- Enthalpy of Vaporization: 8.19 kJ/mol
- Enthalpy of Fusion: -75 kJ/mol
- Solubility in water: 0.022 mg/ml
- Thermal Conductivity: 0.0339 W/m0C
- Shape: Tetrahedral
All the above-mentioned properties are similar to those of a covalent compound such as low melting and boiling point, low enthalpy of fusion, and low solubility and thermal conductivity. This further strengthens the fact that methane is a covalent compound.
Methane Dipole moment
The four hybrid orbitals in methane are arranged in such a way that the force of repulsion between them is reduced. The bond angle of the sp3 hybrid orbitals is 109.5 degrees.
The CH4 is tetrahedral in shape, and as a result of this arrangement, each bond pair is at an equal distance from one another, i.e. they are symmetrically arranged. As a result, each bond dipole moment balances the other.
Thus the net dipole moment of methane turns out to be zero. Since the dipole moment is zero methane is a nonpolar covalent compound.
To sum up, methane is a covalent compound with a molecular mass of 16 and the simplest of all alkanes. It is a flammable non-toxic gas. It is a tetrahedral molecule that has 4 equivalent C-H bonds. Since the electronegativity difference between carbon and hydrogen is very low, it is a covalent compound.
In this article, I have discussed the basic concepts of chemical bonding and the nature of bonds in methane. Please feel free to ask any questions you may have in the comments section. We will respond as soon as possible.