Carbon Tetrachloride
The name, carbon tetrachloride, seems slightly intimidating. A simple method to remember the molecular formula for the same is to break down the name. Carbon, the first word, has the atomic symbol ‘C,’ and since there is no prefix with it, we can assume that the number of carbon atoms in the molecule is only one. Moving on to the word ‘tetrachloride,’ tetra means 4, and chloride refers to the element chlorine, in totality, meaning 4 atoms of chlorine. Therefore, the chemical formula for carbon tetrachloride is CCl4.
Lewis Structure Meaning
Lewis Structure is a very widely used form of diagrammatically representing any covalently bonded compounds’ electronic configuration. The main purpose of this structure is to provide a visual representation of the atomic structure. Further, it also gives an idea about the electrons’ distribution. An important point about Lewis Structure is that it only shows several valence electrons in the given chemical compound, not the other electrons in lower shells. The Lewis structure consists of a collection of dots and lines and the atomic symbol of the necessary elements. Here, the line represents the bond between a pair of electrons, and the number of lines represents the number of covalent bonds. The dots, on the other hand, represent the valence electrons in the element.
Covalent Bonding
In chemistry, there are majorly 2 types of bonds, ionic bond, and covalent bond. A covalent bond is a chemical bond formed as a result of the sharing of a set number of electrons between the atoms.
Bond Formation in CCl4 molecule
The number of valence electrons in the carbon element is 4, and the number of carbon atoms in the molecule is 1. On the other hand, chlorine is 4 in number and has 7 valence electrons. This means, to attain a stable octet configuration, which is 8 valence electrons, carbon needs 4 electrons, and chlorine needs 1 atom each, making a total of 4 atoms. Therefore, carbon shares each of its 4 atoms with each chlorine atom, and in return, chlorine shares one atom each with carbon. Therefore, the carbon and chlorine electrons end up with 8 electrons, though not exclusive to themselves. Since there is a sharing of electrons, it is a covalent bond formed between the elements. This is the bond formation in the CCl4 molecule.
Drawing the Lewis Structure of Carbon Tetrachloride
As explained above, the bonding between the 2 atoms occurs, where carbon and all the chlorine atoms each get 8 electrons in their valence shell. Since Lewis Structures deals with only the valence electrons or the electrons that participate in the reaction, the drawing will consist only of representing the valence electrons. The figure given below is a depiction of the CCl4 molecule, using Lewis Structure format.
(Source- sciencetrends.com)
Explanation
Carbon, as explained, requires 4 electrons, and each chlorine atom requires 1 electron. Carbon shares one of its electrons to each chlorine atom, and in return, each chlorine shares one of its electrons to carbon, bringing about the stable octet configuration. Due to electrons’ sharing, a covalent bond is formed between the carbon and the chlorine atoms. Since, with each atom, there is sharing of only 1 pair of electrons, it denotes a single covalent bond, and therefore there is only one line used to denote the bond between carbon and chlorine.
Studying the above diagram, we can see that dots are surrounding each chlorine atom. These dots represent the un-bonded electrons of chlorine. Initially, chlorine has 7 electrons in each atom. After it shares an electron with carbon, in return also gaining one, a bonded pair of electrons is formed. The other electrons in the atom which do not participate in the reaction but are still valence electrons are represented as the dots. After giving one electron to carbon, since chlorine is left with 6 electrons, these 6 electrons are represented as dots. Therefore, this is the Lewis Structure of Carbon Tetrachloride.
Molecular Geometry
The geometry of where atoms are represented in the 3-dimensional forms that they are in, in reality. It is always done about the central atom of the molecule. This considers the lone pairs of electrons, like the ones in the above-explained chlorine atom. There are only a few arrangements possible to attain by the molecule. They are tetrahedral, where 4 atoms are present, pyramidal with 3 atoms and one lone pair, bent or angular, with 2 atoms and 2 lone pairs, and linear with one atom and 3 lone pairs.
Case Study of Carbon Tetrachloride
Carbon Tetrachloride consists of 4 atoms, and hence, by the above-mentioned possible arrangements, it can be concluded as having tetrahedral geometry. Further, studies have shown that the bond angle in CCl4 is 109.5°.
Sources- Socratic.org
Explanation
In this regard, the Valence shell electron pair repulsion theory, better known as VSEPR theory, is used to study the number of electron pairs surrounding the central atom. Using the conclusion derived there, the geometry of the atom can be predicted. This model is used here to understand the structure of the Carbon Tetrachloride atom.
The above-explained Lewis Structure shows exactly 4 electron regions around the carbon atom, which is occupied by the chlorine atom. According to the VSEPR model, it states that electron regions around the central atom try to put between themselves the maximum distance. This is because they are all repulsive forces due to having like charges of the electrons. In CCl4, to have the atoms as far away from each other as possible, there is only 1 possible solution: the electrons must point towards the corners of the tetrahedron. The bond angle so formed will be at 109.5 °
An important factor to consider as to why all the angles will be the same is because each chlorine atom has the same number of electrons. Each electron in an atom has the same amount of charge. Thus, all the chlorine atoms will apply the same amount of force to the carbon atom, hence having the same bond angles.
The structure will be, hence, tetrahedral.
