9 Facts On KrCl4 Lewis Structure & Characteristics:Why & How

KrCl₄ or krypton tetrachloride is a tetra-coordinated halogenated compound having a molar mass of 225.61 g/mol. Let us discuss KrCl₄ in detail.

KrCl₄ is a compound of the inert element of Kr, and Kr generally cannot react with other elements but due to the presence of electronegative Cl atoms the threshold energy between them is almost equal. The molecule is reactive due to the presence of four electronegative atoms and there are four sigma bonds.

Let us have a look at some important topics of KrCl₄ like lewis structure, hybridization, bond angle, and valence electrons with proper explanations in the following article.

1. How to draw the KrCl₄ lewis structure

Lewis’s structure of KrCl₄ can give us a clear idea about the molecular property of KrCl₄. Let us try to draw the lewis structure of KrCl₄ in different following steps.

Counting the valence electrons

Counting the valence electrons for a molecule is the first redrawing drawing its lewis structure properly. Here the total valence electrons are 36. Now we can explain these valence electrons, by adding valence electrons of Kr as 8 and for four Cl atoms as 7 each, and we just added them together.

Choosing the central atom

Choosing the central atom for drawing the lewis structure is another important step. Here Kr is chosen as the central atom because of two reasons. The first reason is the size of Kr is larger than Cl so it can accumulate all the atoms surrounding itself and the second reason Kr is more electropositive than Cl.

Satisfying the octet

Always it should be checked while drawing lewis’s structure that every atom should obey the octet rule by completing its valence orbital either accept or share electrons from others. So, here Kr has four electrons shared with four Cl atoms and two pairs of lone pairs and each Cl shares one electron to follow the octet.

Satisfying the valency

To obey octet total electrons required for KrCl₄ are 8+(4*8) = 40 but total valence electrons are 36, so to satisfy the valency of each atom we should add ½(40-36) = 2 bonds, but Kr is hexavalent so it forms four sigma bonds with four Cl atoms and two lone pairs and each Cl forms one bond satisfying their mono valency.

Assign the lone pairs

In the last step, we assign the non-bonded electrons over respective atoms. Those electrons are coming lastly after satisfying the valency. Kr has 8 valence electrons and only four electrons are involved in the bond formation. The remaining four electrons and six electrons of each Cl exist as lone pairs over them.

2. KrCl₄ lewis structure shape

Lewis structure shape is very particular for that molecule who has the same environment. Now we try to learn about the shape of KrCl₄ in the following section.

The Shape of the KrCl₄ is square planar according to the following table,

Due to the presence of two pairs of lone pairs, it is an AX₄E₂ type of molecule as per VSEPR (Valence Shell Electrons Pair Theory) and it adopted a square planar shape but its geometry is octahedral. Four Cl atoms present four corners of the square planar moiety.

3. KrCl₄ valence electrons

With the help of valence electrons, each atom can form a stable bond with another, and also the valency will be justified. Let us calculate the total valence electrons for KrCl₄.

The total valence electrons of KrCl₄ is 36 because 8 electrons come from Kr and for each Cl is 7, so for 4 Cl atoms the numbers are 28, and we just add them by their stoichiometric ratio. So, the valence electrons of KrCl₄ are the summation of each atom.

• Let us calculate the total valence electrons for the system separately.
• The valence electrons for central Kr are 8
• The valence electrons for the surrounding Cl atom are 7
• So, total valence electrons for KrCl₄ is 8+(7*4) = 36

4. KrCl₄ lewis structure octet rule

To satisfy the valency of each atom they obey the octet after the bond formation by completing their valence orbital. Now discuss the octet of KrCl₄ in detail.

Kr already completed its octet as it is a noble gas and its configuration is [Ar] 3d¹⁰ 4s² 4p⁶ and Cl needs to complete the octet during the bond formation. Because its valence shell is not completed as its configuration is [Ne]3s²3p⁶. During the bond formation, each Cl shares one electron and completed its octet.

To obey the octet for p block Kr and Cl, the total need of electrons will be 8+(4*8) =40. But the valence electrons are 36, so the remaining electrons are accumulating by 4/2 = 2 bonds to satisfy their valency. By completing the octet Kr, as well as Cl, are satisfied by their stable valency by forming a single bond.

5. KrCl₄ lewis structure lone pairs

Lone pairs are those valence electrons that are not participating in the bond formation they are non-bonded electrons. Let us count the lone pairs of KrCl₄.

KrCl₄ has 14 pairs of lone pairs or 28 lone pairs of electrons present which are coming from the Kr and Cl. Because Kr has 8 valence electrons and only 4 electrons are being used in bond formation. In Cl, there are 7 valence electrons and only 1 electron is used in bond and the rest electrons exist in lone pairs.

• Lone pairs are calculated by the following formula, non-bonded electrons = valence electrons – bonding electrons.
• The lone pair over Kr is, 8-4 = 4
• The lone pairs over Cl is, 7-1 = 6
• So, the total lone pairs of KrCl₄ is 4 + (6*4) = 28 lone pairs of electrons.

6. KrCl₄ lewis structure angle

A bond angle is that angle makes by the atoms which are present in a molecule for proper orientation and shape. Now calculate the bond angle of KrCl₄ in the next part.

The bond angle Cl-Kr-Cl is perfect 90⁰ as because it exists as a square pyramidal shape so the bond angle is the ideal value. All the Cl atoms make the perfect 90⁰ bond angle with central Kr and the lone pairs present over Kr are far away due to the larger size of Kr. So there is no chance of lone pairs repulsion.

• Actually, the bond angle is predicted by the bents rule of hybridization, COSθ = (p-1)/p.
• The hybridization of KrCl₄ is sp³d², so p character is 3/6^th or ½.
• So, the bond angle is, COSθ = [(1/2)-1]/(1/2)
• Θ = COS^-1(-1) = 180⁰
• So the bond angle is 180⁰-90⁰ = 90⁰.

7. KrCl₄ lewis structure formal charge

With the concept of formal charge, we can predict the magnitude of charge and which atom accumulates that can be calculated. Let us calculate the formal charge for KrCl₄.

The formal charge of KrCl₄ is 0 because the net formal charge possessed by the individual atoms is 0 and for this reason, the total formal charge is 0. The molecule is stable and each atom present over the molecule is satisfied by its oxidation state and valency, so no charge will appear on the molecule.

Let us check the value of the formal charge present over H or P by the formula, F.C. = N_v – N_l.p. -1/2 N_b.p.

• The formal charge over the Kr atom is, 8-4-(8/2) = 0
• The formal charge of the over Cl atom is, 7-6-(2/2) = 0
• So, from the above data, it is confirmed KrCl₄ is an electrically stable molecule with 0 formal charges.

8. KrCl₄ lewis structure resonance

Resonance is the delocalization of electron clouds through different skeleton forms of the molecule. Let’s see whether is possible for a KrCl₄ resonating structure or not.

KrCl­₄ shows resonance due to the presence of lone pairs over Cl acts as excess electronic clouds and can be delocalized over the Kr through the bond. KrCl₄ shows generally two resonating structures. One is more stable and another is less stable based on the number of covalent bonds and charges.

Structure I is more stable as it contains the same number of covalent bonds as structure II but no charge appears over the molecule. But structure II contains one double bond between Kr and Cl but the positive charge appears over the electronegative Cl atoms which is a destabilizing factor and it has a lower contribution.

9. KrCl₄ hybridization

Hybridization is a theoretical concept by which the mixing of atomic orbitals forms a new hybrid orbital of equivalent energy. Let us predict the hybridization of KRCL4.

KrCl₄ is sp³d² hybridized which is confirmed in the following table,

• We can calculate the hybridization by the convention formula, H = 0.5(V+M-C+A),
• So, the hybridization of central Kr is, ½(8+4+0+0) = 6 (sp³d²)
• One s orbital, three p orbitals and two d orbitals of Kr are involved in the hybridization.
• The lone pairs over Kr are also involved in the hybridization.

10. Is KrCl₄ polar or nonpolar?

Polarity or non-polarity depends on the presence of the dipole-moment created by the atoms of the molecule. Let us see whether KrCl₄ is polar or not.

KrCl₄ is a non-polar molecule because of its symmetric shape of the molecule. All the directions of the dipole moment will cancel out each other due to the symmetric shape of the molecule. The magnitude of dipole-moment is always the same because all the surrounding atoms are Cl.

Conclusion

KrCl₄ molecule is more reactive because all the sigma electron density of each bond is being dragged away to the electronegative Cl site. So, the bonds become weaker and easily be cleaved and it is used as a chlorinating agent in organic reactions.

Biswarup Chandra Dey

Hi……I am Biswarup Chandra Dey, I have completed my Master’s in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.