KrF2 or Krypton difluoride is made up of Krypton and Fluorine and is one the first compounds of Krypton. It is a colorless solid which is highly volatile and thermally unstable.
Although it decomposes at room temperature, it can be stored indefinitely at -78 degrees Celsius. KrF2 reacts vigorously with Lewis acids to form KrF+ and Kr2F3+ salts.
The molar mass of KrF2 is 121.795 g·mol−1.
The density of KrF2 is 3.24 g cm−3.
KrF2 is primarily used as an oxidizing and fluorinating agent because of its ability to oxidize even gold to its +5 oxidation state.
It can be synthesized using the following methods:-
1. Electrical Discharge – This was the first method used by Turner and Pimentel.
2. Proton Bombardment
3. Hotwire method
4. Photochemical synthesis
Now that you have a basic idea of KrF2 it’s time to learn about its Lewis structure, hybridization, and molecular shape.
KrF2 Lewis Structure
Before we write down the steps to draw the Lewis structure of KrF2, we will take a look as to how the Lewis structure of KrF2 should look like.
The outermost electrons in the shell of an atom are termed valence electrons. We will use valence electrons as our main guide in drawing the Lewis structure.
The Lewis structure of KrF2 shows that K is surrounded by 3 lone pairs of electrons and forms single bonds with each of the F atoms.
Now we start looking at the steps required for drawing the Lewis structure:-
1. We count the total number of valence electrons of the whole molecule. If you don’t remember the valence electrons of a particular atom you can use the periodic table as a reference.
2. Next we find the central atom of that particular molecule.
3. Now we start arranging these electrons as lone pairs that signify a chemical bond with each atom.
4. Next step is to make sure that each atom completes its octet/duplet. So we arrange the remaining valence electrons keeping the above point in mind.
5. To make the molecule more stable we can convert lone pairs into double or triple bonds.
While doing this we should always check the formal charge of each atom and make sure that it is the lowest possible.
The best Lewis structure should have each atom with a neutral charge (0). The formula for calculating formal charge is given below:-
1. Let us count the total number of valence electrons for the molecule KrF2.
Kr belongs to group 8. Group 8 consists of noble gases which are highly stable and so have 8 valence electrons. F belongs to group 7 and since there are two atoms of F, we have 7×2= 14 valence electrons.
Hence the total number of valence electrons for the molecule KrF2 is 8+14= 22 valence electrons.
2. A central atom should have:-
- The highest valence factor.
- The highest number of bonding sites.
In KrF2, it’s obvious that Kr is the central atom.
3. Now we start arranging the electrons as lone pairs on each atom so that it forms a chemical bond. Since there are only two atoms of F, only 4 valence electrons are used up.
4. Now we start arranging the remaining valence electrons around each atom so that it completes its octet. When we finish the above step we notice that only 16 valence electrons have been used up.
So, the remaining 6 valence electrons will act as lone pairs on the central atom Kr. This is an example of an exception to the octet rule.
We notice that Kr can hold more than 8 valence electrons and this is due to the fact that elements below period 3 can have an expanded octet (more than 8 valence electrons) which serves as an exception to the octet rule. Hence Kr has 3 lone pairs on it and can hold more than 8 valence electrons.
5. Now you may ask why we didn’t convert the lone pairs into double or triple bonds? A valid question indeed!
Remember that I had stated earlier that the best Lewis structure should ideally have each atom with a charge of 0. If we check the formal charge of each atom of KrF2 it turns out to be 0.
However, if we convert the lone pairs into double or triple bonds, the formal charge is not the lowest possible. Hence that molecule will be quite unstable.
Thus, this Lewis structure of KrF2 with 3 lone pairs has the highest stability with each atom having a formal charge of 0.
Hybridization is an important aspect when it comes to understanding the nature of the chemical bonds of a molecule. Hybridization helps us to find a more stable molecule by minimizing the energy of the molecule.
The Hybridization of KrF2 is Sp3d.
Hybridization of a molecule can found using two methods:-
1. The theoretical way:-
Hybridization of any molecule can be found by adding the number of bonded sites and the number of lone pairs of the central atom.
The value of Hybridization (H) is determined by:-
If H=2 then it is sp hybridized.
If H=3, then it is sp2 hybridized.
H=4 means that it is sp3 hybridized.
H=5 means that it is sp3d hybridized.
And H=6 means that it is Sp3d2 hybridized.
We already know Kr is the central atom in KrF2. It makes one sigma bond with each F atom and has 3 lone pairs surrounding it. So adding the number of bonds and lone pairs we get the value of H as 2+3 = 5, which means that KrF2 is Sp3d hybridized.
2. The formula part. Although the theory part is much easier to remember you can also use the formula as a confirmation to your answer.
The formula to find the Hybridization of any molecule is given below:-
H= Hybridization of the central atom of the molecule
V= Number of Valence electrons of the central atom.
M= Number of monovalent atoms bonded to the central atom.
C= Charge on cation or more electropositive atom.
A= Charge on anion or more electropositive atom.
In KrF2, we know that Kr is the central atom. So V =8 (valence electrons of Kr). Since F is a monovalent atom and there are two F atoms, M = 2.
Since the overall charge of the molecule is neutral, both and C and A will be zero. Hence using the formula we get,
H=5, indicating that KrF2 is Sp3d hybridized.
Thus we found out the Hybridization of KrF2 using 2 simple methods.
KrF2 Molecular Geometry
The molecular shape as the name suggests is used to determine the shape of a molecule and its bond angles. The molecular shape is different from molecular geometry.
Molecular geometry takes into account the electrons as well when determining the geometry.
The geometry of KrF2 is trigonal bipyramidal.
The molecular shape does take into account the lone pairs on the central atom. Thus, the molecular shape of KrF2 is linear. The bond angle formed between each atom is 180 degrees.
The notation AXN can be used to determine the molecular shape of any molecule. A denotes the number of central atoms. X denotes the number of atoms that are bonded to the central atom.
And finally, N denotes the number of lone pairs or the non-bonding electrons of the central atom.
In KrF2, A=1 as Kr is the only central atom.
X= 2 since there are 2 atoms of F attached to the central atom.
N will be 3 as there are 3 lone pairs sitting on the central atom Kr. Thus using the above formula, we get the shape for KrF2 as AX2N3.
If we check this formula in the VSEPR chart we see that KrF2 has a linear shape.
As mentioned above, the Kr is the central atom connected with 2 F atoms on both sides linearly forming a symmetrical shape of the KrF2 molecule. Moreover, both F atoms are identical having an equal electronegativity.
As a result, both F atoms pull the charge with equal force and have equal charge distribution. Both dipoles act in opposite directions to cancel out each other. This results in a net-zero dipole moment.
Thus, the KrF2 molecule is non-polar in nature.
In this article, we have discussed the Lewis structure, hybridization, and molecular shape of KrF2. So now you should be quite thorough with the basics of the KrF2 molecule.
If you have any doubts regarding any of the points please feel free to talk to me.