XeCl4 is known to be the first-ever discovered binary compound. Xenon tetrachloride is an unstable organic compound. It has a molecular mass of 207.2836 g mol-1. It also has a solid white appearance with a density of 4.040 g cm-3. The melting point of XeCl4 is 117°.
Unlike other Noble gases or halides, XeCl4 cannot be synthesized by combining the elements or by substitution of other elements. A decay technique is used for its synthesis. The reaction for the synthesis of XeCl4 is as follows:
Xe + 2Cl2 —-> XeCl4
The electrons situated in the outermost shell, or energy level, of an atom, are known as valence electrons.
They can be transferred or shared with other atoms during the process of chemical bonding.
In the case of XeCl4 Xenon carries 8 electrons in its outermost shell while each of the Chlorine atoms has 7 valence electrons. Hence, it contains 36 electrons in its valence shell.
The noble gases are the least reactive elements of the periodic table. They have a valence shell containing eight electrons which are responsible for their stability.
The atoms of all other elements of the periodic table also tend to become stable by having eight electrons in their outermost energy level. This is referred to as the octet rule. This was proposed by Kossel and Lewis in 1916.
Usually, the atoms try to acquire the electronic configuration of their nearest noble gas to become stable. It is owing to this tendency of atoms that they participate in bond formation.
The only exceptions to this rule are Helium and Hydrogen. Helium is a noble gas that is stable with two electrons in its valence shell.
Hydrogen also follows the standards of its nearest noble gas (helium) and becomes stable after acquiring two electrons.
Lewis Structure of XeCl4
G.N. Lewis introduced Lewis structures in 1916. These are the pictorial representation of the valence electrons around an atom.
According to these structures, the symbol of the element represents the nucleus as well as the electrons in the inner shells, while the valence electrons are represented by using dots.
The Lewis structure of XeCl4 is as shown below:
As per the above Lewis structure for the XeCl4 molecule, all the Chlorine atoms that initially carried seven valence electrons form a single bond with Xenon and now have eight electrons.
However, Xenon that already had a complete octet now carries more than eight electrons in its valence shell i.e. 12.
Due to the presence of empty 5d-orbitals Xenon is able to expand its octet i.e. it is capable of accommodating more than eight electrons in its valence shell.
Drawing Lewis Structure of XeCl4
In this section, we will try to draw the Lewis structure of the XeCl4 molecule, step by step:
Step 1: First of all, we will calculate the total number of valence electrons present in this molecule.
In the case of the XeCl4 molecule, Xenon being a member of group 18 of the periodic table carries eight valence electrons while Chlorine being a member of group 17 carries 7 electrons in its valence shell.
Calculating the total number of valence electrons:
Xe = 8 valence electrons
Cl = 7 X 4 = 28 valence electrons
Therefore, Total = 36 valence electrons
Step 2: In the next step, we will have to choose the central atom for this molecule.
To draw the Lewis structure, the central atom is considered the base to which all other atoms of the molecule are attached.
Mostly, the least electronegative atom of a molecule is chosen as the central atom. In the case of XeCl4, Xenon is the central atom.
Step 3: Now, we will connect all the other atoms of this molecule to the central atom, with the help of single bonds.
This helps us estimate the number of electrons further needed to complete the octet of all the involved atoms.
Step 4: In the above structure, every single bond represents a shared pair of electrons. As Chlorine already had seven electrons in its valence shell, the octet of all the Chlorine atoms is now complete.
Step 5: Xenon which already had 8 valence electrons has now expanded its octet to house 12 electrons in its outermost shell as explained in the previous section.
Step 6: Therefore, the final Lewis structure of XeCl4 appears as follows:
Step 7: Now, when we have arrived at our final structure, we need to validate our findings. To authenticate a Lewis structure the formal charge of the molecule is taken into account.
The Formal charge is a hypothetical concept the value of which determines the correctness of a Lewis structure.
If the value of formal charge for every individual atom of a molecule is zero, the structure is considered correct.
The formula for calculation of formal charge is given by:
Formal Charge (FC) = [Total no. of valence e– in Free State] – [Total no. of non-bonding e–– 1/2 (Total no. of bonding e–)]
Step 8: Calculating the formal charge on the XeCl4 molecule:
For a Xenon atom, the number of valence electrons in the free state = 8
Number of non-bonding electrons = 2
Number of bonding electrons = 12
Therefore, the formal charge on Xenon atom = 8 – 2 – ½(12)
For a Chlorine atom, the number of valence electrons in the free state = 7
Number of non-bonding electrons = 6
Number of bonding electrons = 2
Hence, the formal charge on the nitrogen atom = 7 – 6 – ½(2)
The net-zero formal charge on the XeCl4 molecule is an indicator that the final lewis structure derived by us is correct.
XeCl4 Molecular Geometry
The Valence Shell Electron Pair Repulsion Theory explains the molecular geometry of different molecules.
This theory was earlier developed by Sidgwick and Powell in 1940 and was further improved by Gillespie and Nyholm in 1957.
As per this theory, in a polyatomic molecule, the position of different atoms inside the molecule is determined by the number of electron pairs, both bonding, and non-bonding, in their valence shells.
This theory postulates that a certain force of repulsion exists between the negatively charged electrons present inside a molecule.
The extent of this force is maximum between lone pair-lone pair and minimum between bond pair-bond pair of electrons.
Further, the extent of repulsion is also regulated by the difference in electronegativity of the central atom and other atoms participating in the formation of the molecule.
In the case of XeCl4, more than one lone pair is present on the central atom as well as all the Chlorine atoms. Therefore, the shape of this molecule would deviate from its ideal geometry which is octahedral.
Owing to the same electronegativity of all the Chlorine atoms, as well as the same number of bond pairs and lone pairs of electrons, these will exist at equal distances from each other. This means that the geometry of this molecule should be square planar.
Let us verify this, using the following chart depicting the shapes of molecules based on the number of bonding groups and lone pair of electrons present in a molecule:
Therefore, according to VSEPR theory, for XeCl4 the electron geometry is octahedral and molecular geometry is square planar. All the Chlorine atoms are located at an equal distance from each other at an angle of 90°.
In an attempt to explain the geometry of polyatomic molecules, Linus Pauling put forth the concept of hybridization.
As per him, during the formation of a molecule, the orbitals of different atoms combine to form a new set of orbitals. These are known as hybrid orbitals and the phenomenon is known as hybridization.
Here, another concept known as “Steric number” comes into the picture. This is used to calculate the hybridization of a molecule. The formula for steric number is given as:
Steric No. = Sigma bonds (σ) present on the central atom + lone pair present on the central atom
Therefore, the Steric number for the XeCl4 molecule can be calculated using this formula:
In XeCl4, Xenon is the central atom. Therefore,
Steric number of XeCl4 = 4 + 2 = 6
Now, we can determine the hybridization state for the XeCl4 molecule using the following table:
As the steric number for XeCl4 is 6, the hybridization state of this molecule is Sp³d².
Now, let us look at the distribution of electrons inside different orbitals of this atom:
• The hybridization state of the Xenon atom is sp3. This means that the electrons inside this atom are distributed in different orbitals as follows:
• In the excited state, the electrons in the 5p orbital jump into the vacant 5d orbitals.
• The four valence electrons of the Chlorine atoms pair with these excited electrons, thus forming a sigma bond each.
• Therefore, the hybridization of the XeCl4 molecule becomes sp3d2.
In chemistry, polarity represents the separation of electric charge leading to the molecule or its chemical groups possessing an electric dipole moment, consisting of a negatively charged and a positively charged end.
In the case of the XeCl4 molecule, there are four Chlorine atoms attached to the central Xenon atom. The square planar geometry indicates that each of these atoms is placed opposite to each other, at four corners of a square, at an angle of 90°.
Therefore, the dipole moment generated due to the electronegativity difference between Chlorine and Xenon atom gets canceled amongst itself. Hence, the net dipole moment of the XeCl4 molecule becomes zero.
• The Lewis structure of XeCl4 is:
• The molecular geometry of XeCl4 is square planar.
• The hybridization of XeCl4 is sp3d2.
• The net dipole moment of XeCl4 is 0 D.