VIDEO To understand any molecule’s chemical and physical properties, it is essential to know the Lewis structure and its molecular geometry. In this blog post, we will go through the total number of valence electrons, Lewis dot structure, shape and more. PCl3 Valence Electrons One needs to know the total number of valence electrons for a molecule to construct the Lewis Dot Structure. To calculate the total number of valence electrons of this molecule, we will add up the valence electrons of both Phosphorus and Chlorine atoms. Phosphorus has five valence electrons. Chlorine has seven valence electrons, but as there are three atoms of Chlorine, we will multiply this number by 3. Total number of valence electrons of PCl3: Valence electrons of Phosphorus + Valence electrons of Chlorine = 5 + 7*3 = 26 Phosphorus Trichloride (PCl3) has a total of 26 valence electrons. PCl3 Lewis Structure Now that we know the total number of valence electrons for Phosphorus Trichloride, we will start drawing the Lewis Dot Structure for this molecule. The Lewis Structure for any molecule helps to know the arrangement of valence electrons in the molecule, bond formation and the number of bonding as well as nonbonding pairs of electrons. The electrons that participate in forming bonds are called bonding pairs of electrons. In contrast, the ones that do not participate in bond formation are called lone pair of nonbonding pair of electrons. Here we will first place the atoms along with its individual valence electrons to understand the bond formation. So, Phosphorus atoms will take the central position as it is less electronegative than the Chlorine atom. Place Phosphorus in the centre and all the other chlorine atoms around it. To show bonds between Phosphorus and Chlorine atoms, draw a straight line to show the bond formation. Each bond uses up two valence electrons which means we have used a total of six valence electrons. Chlorine atom shares one valence electron of Phosphorus to complete its octet. Now if you look at the molecule, every Chlorine atom has a complete octet as it has eight valence electrons in its outer shell. However, Phosphorus is left with two valence electrons that do not participate in forming any bond. This pair of electrons is the nonbonding pair of electrons for this molecule. PCl3 Electron Geometry When you look at the Lewis Structure of the molecule, you can see that electrons’ arrangement is in a tetrahedral geometry. Hence the electron geometry of Phosphorus Trichloride is tetrahedral. PCl3 Hybridization The hybridization of PCl3 can be determined once we know the Lewis dot structure of this molecule. Here three atoms are bonded with Phosphorus atom, which means that there formation of hybrid orbitals that accommodate these shared electrons. Phosphorus’s electronic configuration in its ground state is 1s Chlorine 2 2s 2 2p 6 3s 2 3p 2 as the total number of valence electrons is 5. When it is in an excited state, one of the electrons in the s-orbital moves to the d-orbital and the valence electrons of p orbitals get unpaired to move to the higher orbitals. The electronic configuration of the Phosphorus atom in excited state is 1s 2 2s 2 2p 6 3s 2 3px 1 3py 1 3pz 1 . During bond formation, the electrons get paired up with the unpaired valence electrons. The other two valence electrons that don’t participate in bond formation move to another hybrid orbital. So as four hybrid orbitals are formed, the hybridization of PCl3 is sp3. PCl3 Molecular Geometry Once you know the molecule’s electron geometry, it is relatively easy to guess the molecular geometry. Here the molecular geometry of Phosphorus Trichloride is . trigonal pyramidal PCl3 Bond Angle As per the molecular geometry of the molecule, the bond angle of PCl3 should be 109 degrees. But as there is one lone pair of electrons on the central phosphorus atom, the bond angle will reduce from 109 degrees because of the repulsive forces of the lone pair. As a result, the bond angle of Cl-P-Cl gets deviated and is less than 109 degrees. PCl3 Shape Phosphorus Trichloride has a trigonal pyramidal shape as the electrons are arranged in a tetrahedral geometry. Is PCl3 polar or nonpolar? The polarity of any given molecule depends on its molecular geometry, net dipole moment in the molecule, and lone pairs in the molecule. When there is a formation of poles in the molecule or partial distribution of charges, the molecule is said to be a polar molecule. Here, the molecular geometry of PCL3 is trigonal pyramidal with the partial charge distribution on the Phosphorus. It is a well-known fact that if there is a vast difference in electronegativity, there are more chances of polarity. The Phosphorus has an electronegativity value of 2.19, and Chlorine comes with 3.16. So, the end difference is 0.97, which is quite significant. If the difference is between 0 to 0.50, then it will be nonpolar. But, as the difference here is more than 0.5, PCL3 is a polar molecule. Concluding Remarks To summarise this blog we can say that Phosphorus Trichloride’s Lewis structure includes three single bonds between Phosphorus and Chlorine atoms along with one lone pair of electrons on the central atom. The hybridization of Phosphorus is sp3, and the bond angles of Cl-P-Cl are less than 109 degrees. It has a tetrahedral electron geometry and trigonal pyramidal shape. I hope that this blog post helps you understand all the aspects of this molecule in depth. Let us know in the comments below which other molecule’s Lewis structure you would like to learn.