This article discusses pf3 lewis structure and its hybridization, shape, bond angle, and relevant detailed explanations.
PF3 is a covalent molecule where P is located at a central position and surrounded by three F atoms. P and F are covalently bonded along with sp3 hybridization. The molecule is in trigonal pyramidal shape but the geometry of the molecule is tetrahedral. F-P-F bond angle is around 970 instead of 109.50.
PF3 is a neutral compound so no charge appears on this compound. Among the five valence electrons of P, only three of them participate in bond-forming and the rest two are non-bonded electrons and appear as lone pairs. PF3 is a polar molecule. So, here we will learn about the pf3 lewis structure and other facts about it in detail.
Some facts about Phosphorus trifluoride
The molar mass of PF3 is 87.98 g/mol, density is 3.91 g/l. The melting point and boiling point of PF3 are 121.7 K and 171.4 K respectively. Its shows a chemical shift value at -34 in 19F NMR. PF3 is normally synthesized via the halogen exchange reaction between phosphorus trichloride and various metal fluorides such as ZnCl2 or Cacl2.
Method of drawing the lewis structure for PF3
Before proceeding with the lewis structure of PF3 at first, we should know what lewis structure is. Lewis structure or lewis dot structure is one kind of representation of a molecule showing the valence electrons, especially in the covalent bond.
There are some points are should keep in mind to drawing the lewis structure of a molecule.
- First, we need to calculate the valence electrons of every individual atom in the molecule and added together.
- If the molecule is bearing a negative charge then an extra electron equal to the negative charge is added.
- If the molecule is cationic then an equal number of electrons should be removed from the molecule.
- Next, we should identify the central atom by its electronegativity, Normally, a competitively more electropositive atom should be the central atom.
- Now all the atoms in the molecules are connected via a single bond.
- Then lone pairs are assigned to the atom, generally lone pairs are assigned to the electropositive atom.
- After assigning the lone pairs if the octet of an atom is not completed then a double or triple bond should be drawn in order to complete the octet. If required the lone pairs should be converted to the bond pairs to satisfy the octet.
In this structure of phosphorus trifluoride, we can see one Phosphorus atom is surrounded by three Fluorine atoms. The electronic configuration of Phosphorus is 1s22s22p63s23p3, so taking into consideration the valence electrons of Phosphorus is five among them three are bond pairs and two appear as lone pair, and the electronic configuration of Flourine is 1s22s22p5, so the valence electrons of each fluorine atom are seven and appear as three lone pairs and one bond pair. So, the total number of valence electrons for the PF3 molecule is 5 + (7*3) =26.
PF3 lewis structure shape
In PF3 molecule electron density lies around the central Phosphorus atom and there are three bond pairs and one lone pair are present.
In this case phosphorus trifluoride, the structure is trigonal pyramidal. In trigonal pyramidal structure, one phosphorus atom is present at the central position and three fluorine atoms are present at the three corners.
PF3 lewis structure formal charge
The formal charge is defined as the charge over a particular molecule assuming that all the atoms have the same electronegativity.
F.C. = Nv – Nl.p. -1/2 Nb.p.
Nv = number of electrons in the valence shell of the free atom
Nl.p = number of electrons in lone pair
Nb.p = number of electrons involved in the bond formation.
So the formal charge of the PF3 molecule is 26-(3*6)-6 = 2
Number of lone pairs in PF3 Lewis structure
The total number of lone pairs in Phosphorus Trifluoride is the sum of individual lone pairs of Fluorine atoms and Phosphorus atoms. The number of lone pairs over Phosphorus is one and each Fluorine contains three lone pairs. So, the total lone pairs of phosphorus trifluoride are 1+ (3*3) =10.
Hybridization of PF3
What is Hybridization?
It involves the mixing of atomic orbitals having similar energy to form an equal number of mixed orbitals or hybrid orbitals and these hybrid orbitals are so oriented in space that they can overlap with suitable orbitals of the subsequent. If the orbitals are of the same energy is called equivalent hybridization and if the mixed orbitals are of different energy then it is called non- equivalent hybridization.
|Structure||state of hybridization of central atom||Bond angle|
|Linear||sp /sd / pd||1800|
|Trigonal bipyramidal||sp3d/dsp3||900 (axial), 1200(equatorial)|
In the ground state, the electronic configuration of Phosphorus is [Ne]3s23p3. We know the maximum number of electrons occupying in p orbital is 6. So here lack of electrons is 3. Now the electronic configuration of fluorine is [He]2s22p5.
So, to complete the octet of Phosphorus it needs 3 more electrons, and to complete the octet of Fluorine it removes one electron. So, each Fluorine gives one electron to the vacant p orbital of Phosphorus and completed its octet and after taking three electrons even Phosphorus completes its octet too.
So, a stable bond is a formation that happens via the mixing of s and three p orbitals. Phosphorus has two electrons in its 3s orbital as a lone pair and its 3p orbital is filled with six electrons (3px,3py,3pz, three on its own and three from each fluorine). So here in hybridization one s orbital and 3 p orbital is involved. So, the mode of hybridization is sp3.
In the case of hybridization, we always consider the single bond or sigma bond, not the π bond or multiple bonds. From the above chart, we can easily predict the structure of the PF3 molecule is tetrahedral as its hybridization state is sp3. In the case of structure, we consider the surrounded atoms as well as lone pairs also. But in shape, we consider only surrounded atoms by the central atom. So, the molecule is trigonal pyramidal in shape, not trigonal planner because due to the presence of lone pair the F-P-F bond angle is not even close to 1200. For an ideal tetrahedral molecule, the bond angle is 109.50.
PF3 Bond Angle
From the hybridization table, we can see that for sp3 hybridized molecule bond angle is 109.50. But in the case of the PF3 molecule, the bond angle is nearly 970 (actually 96.30) although the molecule is sp3 hybridized. This abnormality of bond angle can be explained for two reasons. One is lone pair-lone pair repulsion and one is Bent’s rule.
In the PF3 molecule, there will be a lone pair over Phosphorus present in sp3 hybridized orbital and three fluorine have three pairs of lone pair. So here high chance of lone pair- lone pair repulsion. To avoid this repulsion sp3 hybridized lone pair pushes the P-F bond away from it and therefore decreases the F-P-F bond angle. The repulsion is so high that the bond decreases very much and is close to 970.
PF3 octet rule
According to the octet rule, every atom should complete its valance shell by donating electrons or accepting electrons to gain the nearest noble gas configuration. Phosphorus is a group of VA elements so it has 5 electrons in its outermost shell and Fluorine is a VIIA element so It has 7 electrons in the outermost shell.
So, undergoing hybridization there will be four new hybrid orbitals that will form, this way Phosphorus as well as Fluorine complete their octet and gain the nearest noble gas configuration and form a stable molecule PF3.
PF3 resonance structure
Resonance is a theoretical concept – that introduce to explain the bonding properties of molecules via shifting of the electronic clouds between the atoms in such a way that the main structure of the framework remains unchanged. In fact, it is another bonding model where the actual structure may be represented as the resonance having a hybrid of a number of different canonical forms.
Rules for the most contributing structure
- The most contributing structure should be one that contains the largest number of covalent bonds.
- For more than one structure having an equal number of covalent bonds the one in which more electronegative substituents containing the electronegative charge will have a higher contribution, more electropositive substituents containing the positive charge.
PF3 polar or nonpolar
For the polarity of a molecule, we should first see the dipole moment of that molecule. From the electropositive atom to the electronegative atom dipole moment works. In this molecule Phosphorus is electropositive and Fluorine is electronegative. So, the dipole moment works from Phosphorus to Fluorine. The molecule is trigonal pyramidal so the shape is not symmetrical. Thus, symmetrical charge distribution does not occur. This molecule has a resultant dipole moment. So PF3 is a polar molecule.
Uses of PF3
Having a vacant d orbital of P, PF3 can easily bind with metal with a low oxidation state having a higher number of d electrons. It is a strong π-acceptor ligand due to the presence of three electronegative Fluorine atoms. So, it can participate in many organometallics reactions. So many organometallics reactions can be carried out with the help of PF3.
Frequently asked questions (FAQ)
Why does PH3 have a lesser bond angle than PF3?
Considering the formation of PF3 where three F atoms approach the central p atom along the three axes. When the 3 F atoms come at bonding distance they will suffer steric repulsion due to the lone pair of P as well as F atoms also. Hence the system will go unstable. In order to gain stabilization, the central P atom undergoes sp3 hybridization and the bond angle becomes 970(Bent’s rule).
When the 3 H atoms approach the P center in a similar fashion, it is due to the smaller size of H and larger size of the P atom 3 H atoms will not suffer any steric repulsion. Thus the system is not energies and the px, py, pz orbitals of P are directly involved in the bond formation, and no need for hybridization – thereby accounting for the H-P-H bond angle being around 900.
Is there back bonding possible in PF3 ?
Yes, there is a possibility of back bonding in the PF3 molecule. P has a vacant d orbital and F has 3 pairs of lone pairs. So there will be a high chance of forming dπ-pπ back bonding.
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