How to draw PH3 Lewis Structure? - Science Education and Tutorials

Drawing PH3 Lewis Structure is very easy to by using the following method. Here in this post, we described step by step method to construct PH3 Lewis Structure.

Table of Contents

Key Points To Consider When Drawing The PH3 Structure

A three-step approach for drawing the PH3 Lewis structure can be used. The first step is to sketch the Lewis structure of the PH3 molecule, to add valence electrons around the Phosphorous atom; the second step is to add valence electrons to the three hydrogen atoms, and the final step is to combine the step1 and step2 to get the PH3 Lewis Structure.

The PH3 Lewis structure is a diagram that illustrates the number of valence electrons and bond electron pairs in the PH3 molecule. The geometry of the PH3 molecule can then be predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR Theory), which states that molecules will choose the PH3 geometrical shape in which the electrons have from one another.

Finally, you must add their bond polarities to compute the strength of the P-H bond (dipole moment properties of the PH3 molecule). The Phosphorous-hydrogen bonds in phosphine(PH3), for example, are polarised toward the more electronegative Phosphorous, and because both bonds have the same size and are located around four terminals with one lone pair of electrons and three hydrogen atoms, their sum is non zero due to the PH3 molecule’s bond dipole moment and one lone pair of electron on the Phosphorous atom. The phosphine molecule is classified as a polar molecule.

The molecule of phosphine (with tetrahedral molecular geometry) is tilted, the bond angles between Phosphorous and hydrogen are 107 degrees. It has a difference in electronegativity values between Phosphorous and hydrogen atoms, with Phosphorous’s pull being less than hydrogen’s terminal in the PH3 molecule. As a result, it has the permanent dipole moment. The PH3 molecule has a permanent dipole moment due to an unequal charge distribution of negative and positive charges. The net dipole moment of the PH3 molecule is 1.4 D.

PH3 Lewis Structure: point to remember

The central atom is Phosphorous, which is bordered on four terminals with three hydrogen atoms(downwards in tetrahedral geometry), and one lone pair on the Phosphorous at the top of the tetrahedral geometry. Phosphorous has five outermost valence electrons, indicating that it possesses five electrons in its outermost shell, whereas hydrogen only has one valence electron in its outermost shell. To complete the octet of the Phosphorous atom, a Phosphorous central atom requires three valence electrons. If you’re interested in learning more about the Phosphorous octet rule, please see in our previous post.

Three hydrogen atoms establish covalent connections with the central Phosphorous atom as a result, leaving the Phosphorous atom with one lone pair. There is one lone pair on the Phosphorous central atom that resist the bond pairs of the three P-H. According to VSEPR theory, the electronic repulsion of the lone pair and bond pair leads the PH3 molecule to take on a tetrahedral molecular geometry shape.

The PH3 molecule’s P-H bonds are arranged in asymmetrical order around the tetrahedral molecular geometry, giving rise to the PH3 molecular shape. The PH3 molecule has a tetrahedral molecular geometry because there is electrical repulsion between one lone pair and three bond pairs(P-H) of the PH3 molecule.

Electronegative Difference Calculation of PH3 Molecule:

The Phosphorous atom has an electronegativity of 3.04, while hydrogen has an electronegativity of 2.20 in the PH3 molecule. The difference in electronegativity can be estimated using the method below.

The electronegative value difference between Phosphorous and hydrogen
Electronegativity value of Phosphorous= 3.04
Electronegativity value of hydrogen= 2.20
Difference of electronegativity value between Phosphorous and hydrogen= 3.04 – 2.20 =0.84
Electronegativity difference between P-H bond calculation of PH3 molecule

Due to the difference in electronegativity value of greater than 0.5, the P-H bond of the PH3 molecule becomes polar. Because of this difference in electronegativity, the PH3 molecule’s P-H bond becomes polar. The electronegativity of an atom is the strength with which it may attract bound electron pairs to its side. The polarity of PH3 is discussed in our previous post.

As a result, the P-H bond’s dipole moment is high due to the polarization of the bonds and one lone pair of electrons, and all P-H bonds’ dipoles are arranged in the tetrahedral molecular geometry. The PH3 molecule’s total dipole moment is predicted to be 1.4 D. It has a partial negative charge for the Phosphorous atom and a partial positive charge for the terminal hydrogen atoms.

The electron dot structure of the PH3 molecule is also known as the PH3 Lewis structure. It determines the number of outermost valence electrons as well as the electrons engaged in the PH3 molecule’s bond formation. The outermost valence electrons of the PH3 molecule must be understood while considering the Lewis structure of the molecule.

The Phosphorous atom is the middle element in PH3 molecular geometry, with five electrons in its outermost valence electron shell, whereas the hydrogen atom has one electron in its outermost valence electron shell.

The PH3 molecule has a total of 8 valence electrons as a result of the foregoing above-said reasoning. With the core central Phosphorous atom, the four-terminal with three hydrogen atoms forms covalent bonds, leaving the Phosphorous atom with one lone pair on the top of tetrahedral geometry.

The tetrahedral molecular geometry and structure of the PH3 molecules are similar to that of the methane (CH4) molecule. Because one lone pair of a central Phosphorous atom create interaction with P-H bond pairs. The bond angle of the H-P-H bond in the tetrahedral molecular geometry is approximately 107 degrees. This angle is less than the CH4 molecule bond angle due to the one lone pair of electrons on the PH3 molecule. The P-H bond length is 100 pm(picometer) respectively.

To sketch the PH3 Lewis structure by following these instructions:

Step-1: PH3 Lewis dot Structure by counting valence electrons on the Phosphorous atom

To calculate the valence electron of each atom in PH3, look for its periodic group from the periodic table. The Phosphorous and hydrogen families, which are the 15th and 1st groups in the periodic table, are both made up of Phosphorous and hydrogen atoms. In their outermost shells, Phosphorous and hydrogen have five and one valence electrons, respectively.

Because Phosphorous and hydrogen are members of the periodic table’s Phosphorous and hydrogen family groups, their valence electrons are five and one, respectively.

Calculate the total number of valence electrons in the PH3 molecule’s outermost valence shell. The first step is to determine how many electrons are in the PH3 Lewis structure’s outermost valence shell. An electron in an atom’s outermost shell is known as a valence electron. It is represented by dots in the PH3 Lewis diagram. The PH3 molecule’s core Phosphorous atom can be represented as follows:

Total outermost valence shell electron of Phosphorous atom in PH3= 5
Total outermost valence shell electron of the hydrogen atom in PH3= 1
The PH3 molecule has one central Phosphorous and three hydrogen atoms. Then the total outermost valence shell electrons can be calculated as follows
∴ Total outermost valence shell electrons available for PH3 Lewis structure( dot structure) = 5+3*1= 8 valence electrons in PH3.
calculation of total valence electron of PH3 molecule

Choose the atom with the least electronegative value atom and insert it in the center of the molecular geometry of PH3. We’ll choose the least electronegative value atom in the PH3 molecule to place in the center of the PH3 Lewis structure diagram in this phase. The electronegativity value in periodic groups grows from left to right in the periodic table and drops from top to bottom.

Step-2: Lewis Structure of PH3 for constructing around the central Phosphorous atom

As a result, Phosphorous is the second atom in the periodic table’s nitrogen family group. Hydrogen is the first member of the hydrogen family. The electronegative value of the Phosphorous atom is lower than that of the hydrogen atom in the PH3 molecule. Furthermore, Phosphorous has a five electrons limit since Phosphorous is the most electronegative element in the PH3 molecule.

In the PH3 Lewis structure diagram, the Phosphorous atom can be the center atom of the molecule. As a result, central Phosphorous in the PH3 Lewis structure, with all three hydrogens arranged in the tetrahedral geometry.

Add valence electrons around the hydrogen atom, as given in the figure.

Step-3: Lewis dot Structure for PH3 generated from step-1 and step-2

Connect the exterior and core central atom of the PH3 molecule with three single bonds (P-H). In this stage, use three hydrogen atoms on the outside of the PH3 molecule to the central Phosphorous atom in the middle.

Count how many electrons from the outermost valence shell have been used in the PH3 structure so far. Each P-H bond carries two electrons because each Phosphorous atom is connected to three hydrogen atoms by three P-H bonds. Bond pairings of P-H are what they’re called.

So, out of the total of 8 valence electrons available for the PH3 Lewis structure, we used 6 for the PH3 molecule’s three P-H bonds. The PH3 molecule has one lone pair electron in the center of Phosphorous. We need to put no extra electrons in the molecular geometry of PH3.

Place the valence electrons in the P-H bond pairs starting with the core Phosphorous, three hydrogens, and one lone pair of electrons in the PH3 molecule. In the PH3 Lewis structure diagram, we always begin by introducing valence electrons from the central Phosphorous atom(in step1). As a result, wrap around the central Phosphorous atom’s bond pair valence electrons first (see figure for step1).

Phosphorous requires 6 electrons in its outermost valence shell to complete the molecular stability, 6 electrons bond pairs in P-H bonds. Then two electrons as a lone pair of electrons on the Phosphorous atom of the PH3 molecule are placed in a tetrahedral geometry. Phosphorous already shares 6 electrons to the three P-H bonds. Then place the valence electron in the hydrogen atom, it placed around one electron(step-2). Totally, 3 valence electrons are placed on the three hydrogen atoms of the PH3 molecule.

We’ve positioned 6 electrons around the central Phosphorous atom(step-3), which is represented by a dot, in the PH3 molecular structure above. The Phosphorous atom completes its molecular stability in the PH3 molecule because it possesses 6 electrons in its bond pairs with three hydrogens in the outermost valence shell.

Count how many outermost valence shell electrons have been used so far using the PH3 Lewis structure. Three electron bond pairs are shown as dots in the PH3 chemical structure, whereas three single bonds each contain two electrons. The outermost valence shell electrons of the PH3 molecule are six as a result of the calculation.

The core atom in the PH3 Lewis structure is Phosphorous, which is bonded to the three hydrogen atoms by single bonds (P-H). With the help of three single bonds, it already shares six electrons. As a result, Phosphorous follows the octet rule and has eight electrons surrounding it on the three terminals of the PH3 molecule’s tetrahedral geometry.

How to calculate the formal charge on a Phosphorous atom in PH3 Lewis Structure?

The formal charge on the PH3 molecule’s Phosphorous central atom often corresponds to the actual charge on that Phosphorous central atom. In the following computation, the formal charge will be calculated on the central Phosphorous atom of the PH3 Lewis dot structure.

To calculate the formal charge on the central Phosphorous atom of the PH3 molecule by using the following formula:
The formal charge on the Phosphorous atom of PH3 molecule= (V. E(P)– L.E(P) – 1/2(B.E))
V.E (C) = Valence electron in a Phosphorous atom of PH3 molecule
L.E(C) = Lone pairs of an electron in the Phosphorous atom of the PH3 molecule.
B.E = Bond pair electron in N atom of PH3 molecule
calculation of formal charge on Phosphorous atom in PH3 molecule

The Phosphorous core atom (three single bonds connected to three hydrogen atoms ) of the PH3 molecule has five valence electrons, one lone pair of electrons(two electrons), and six bonding electrons. Put these values for the Phosphorous atom in the formula above.

Formal charge on Phosphorous atom of PH3 molecule = (5- 2-(6/2)) =0

In the Lewis structure of PH3, the formal charge on the central Phosphorous atom is zero.

Summary:

In this post, we discussed the method to construct the PH3 Lewis structure. Need to remember that, if you follow the above-said method, you can construct molecular dot structure very easily.