CCl4 is a poisonous gas that depletes the ozone layer and is often known as a greenhouse gas. It was a popular solvent in organic chemistry, but, it is rarely used today because of its adverse health effects. Henri Victor Regnault, a French chemist, first produced tetrachloromethane in the year 1839. Chloroform and chlorine were combined to make it. These days, tetrachloromethane is manufactured by treating methane with chlorine. The following is the reaction: CH4 (Methane) + 4Cl2 (chlorine) ———> CCl4 + 4 HCl (acid) Is CCl4 (carbon tetrachloride) a covalent compound? In the next part, we’ll find out. Four chlorine atoms and one carbon atom make up a CCl4 molecule. Since each chlorine atom is one electron short of an octet configuration (complete shell) and carbon is 4 electrons short of a complete valence shell of eight, four chlorine atoms share electrons with the four valence electrons of carbon, resulting in full outer shells for all five atoms. The bond so formed between carbon and chlorine is a covalent bond since it is formed by sharing electrons. This makes CCl4 a covalent compound.
As chlorine and carbon atoms share their outer electrons, chlorine attains the electronic configuration of argon and carbon attains that of neon. As a result, while forming covalent bonds both the chlorine and carbon atoms essentially have outer shells with 8 electrons. Well, that was a crisp answer. Now let me discuss the covalent nature of CCl4 in detail. Before we dig into the details of covalent bonds in methane, let’s start from the basics. First, I will explain the types of bonds.
Ionic bonds
An ionic bond formation takes place due to the permanent transfer of valence (outermost) electrons of one atom to another atom. Electrostatic attraction between positively and negatively charged ions causes these bonds to form. The atom which loses electrons becomes a positively charged ion or cation whereas the atom which gains electrons becomes a negatively charged ion or anion.
Covalent Bonds
Elements with extremely high ionization energies can’t lose electrons, and those with extremely low electron affinity can’t accept them. Such elements’ atoms try to share electrons with atoms of other elements or with the same element’s atoms, resulting in an octet arrangement in both valence shells. A covalent bond can be polar or nonpolar based on electronegativity difference.
Non-polar covalent bond
A non-polar covalent bond is formed when two atoms share electrons equally. In a non-polar covalent bond, the electronegativity difference of the bonded atoms is usually very small. It also means that there is no charge separation between those two atoms or that their electronegativity is identical.
Polar Covalent Bond
A polar covalent bond is formed due to the unequal sharing of electron pairs between two atoms. According to the Pauling scale, the electronegativity gap between the bonded atoms should be between 0.4 and 1.7 or approximately 2.
Factors affecting the formation of Covalent Bond
The formation of the covalent bond between the atoms is influenced by several factors as shown below: Let me describe in detail how these factors favor a covalent bond.
Electron affinity
It refers to the energy difference that occurs when an atom gains a valence electron. The formation of a covalent bond is favored when the reacting atoms have comparable electron affinities.
High Ionization Energy
Atoms that have high ionization energies prefer to form covalent bonds. The simple reason is that they can’t form cations. This is because it is very difficult for them to lose their valence electrons, which are needed for ionic bonding. Chlorine has a very high ionization energy of chlorine is 1251.2 kJ/mole while carbon has 1086.5 kJ/mole. Owing to the high ionization enthalpy of both elements it is easier to form a covalent bond between them.
Atomic Size
Another property that facilitates the creation of a strong covalent bond is the smaller atomic size. When it comes to forming covalent bonds between two atoms, the covalent radius is used to determine how far apart the participating valence electrons of both atoms are. Each atom’s covalent radius would be half of the distance between the two nuclei in the case of forming a covalent radius. This is the case since an equal number of valence electrons participate and are present at an equal distance from one another, as well as with an equal force of attraction on the other atom. As a result, the smaller an atom is, the closer it is to the nucleus. The electrons would be under strong molecular attraction making it difficult for them to leave the atom. So instead of completely transferring the electrons through an ionic bond, the atom would prefer a covalent bond via sharing of electrons. The smaller size of both chlorine and carbon atom facilitates the formation of a covalent bond.
Electronegativity
It is an atom’s property that causes it to draw the mutual electron pair towards it. The Pauling scale helps us 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 (In some texts it is mentioned as 1.7). If the difference is less than 2.0 on the Pauling scale, a covalent bond is present. Chlorine has an electronegativity of 3.16, and carbon has 2.55. The electronegativity difference between carbon and hydrogen is 3.16 – 2.55 = 0.61. Due to this difference in electronegativity, the C-Cl bond is polar. As a result, each of the four C-Cl bonds has a dipole moment value too. Let’s see if CCl4 is a polar or non-polar molecule. The outermost shell of the carbon atom has four electrons, and all of them participate in the formation of covalent bonds with four chlorine atoms, leaving no lone pair on the carbon atom.
With one s orbital and three p orbitals, carbon tetrachloride forms sp3 hybridization. The bond angle in the CCl4 molecule is around 109.5 degrees, forming a tetrahedral geometry. The tetrahedral molecular geometry of CCl4 cancels out the dipole moment since all four bonds (C-Cl) are symmetrical and have an equal charge distribution. Thus CCl4 is non-polar.
The number of Valence Electrons
When each of the combining atoms has 5, 6, or 7 electrons in its valence shell, the formation of a covalent bond is preferred. This is why non-metals from the Oxygen, Nitrogen and Halogen families tend to form covalent bonds. The covalent bonding in carbon is a special case which is described briefly below:
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 can’t receive four electrons to turn into a carbon anion (C4-) because six protons cannot carry ten electrons, causing the atom to become unstable.
- Carbon can’t give four electrons to turn into a carbocation (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.
Uses of CCl4
Conclusion
Carbon Tetrachloride or CCl4 is a symmetrical molecule with four chlorine atoms attached to a central carbon atom. It has a tetrahedral geometry. Owing to the high electron affinity and small size of carbon and chlorine atom it forms a covalent C-Cl bond. The bond is a polar covalent bond due to the electronegativity difference. The molecule as a whole is non-polar since the dipole moments are canceled out. In this article, I have discussed the basic concepts of chemical bonding and the nature of bonds in CCl4. Please feel free to ask any questions you may have in the comments section. We will respond as soon as possible.
