P4 Lewis structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar or non-polar
P4 is the chemical formula for tetraphosphorus, also known as white phosphorus. P4 is a homoatomic molecule composed of four identical phosphorus (P) atoms.
It is widely used in the chemical manufacturing industry for synthesizing cleaning agents, pesticides, fertilizers, food additives, etc.
In this article, we have compiled for you important information such as how to draw the Lewis dot structure of P4, what is its molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, polar vs. non-polar concept, and much more.
P4 Lewis structure consists of four identical phosphorus (P) atoms. One P-atom acts as the central atom, while the other three phosphorus atoms act as outer atoms. There are a total of 4 electron density regions around each P-atom, containing 3 P-P bond pairs and 1 lone pair in the P4 lewis structure
Drawing the Lewis dot structure of P4 is not that straightforward because we need to think three-dimensionally in this case.
But don’t worry because we will teach you how to draw the Lewis dot structure of tetraphosphorus (P4) via the step-by-step guide given below.
Steps for drawing the Lewis dot structure of P4
1. Count the total valence electrons in P4
The Lewis structure of a molecule is a simplified representation of all the valence electrons present in it. So, the very first step while drawing the Lewis structure of P4 is to find the total valence electrons present in its concerned elemental atoms.
As P4 is made up of four identical phosphorus (P) atoms, so we just need to look for the position of phosphorus in the Periodic Table of elements. Phosphorus is present in Group V A (or 15) of the Periodic Table. Thus it has a total of 5 valence electrons.
∴ Therefore, the total number of valence electrons available for drawing P4 Lewis structure = 4(5) = 20 valence electrons.
2. Choose the central atom
In this second step, the least electronegative atom out of all the concerned atoms is chosen and placed as the central atom.
But in the case of P4, the situation seems uncomplicated because it involves four identical phosphorus atoms. Hence any one P-atom can be chosen as the central atom while the other three P-atoms are placed in its surroundings, as shown in the figure below.
3. Connect outer atoms with the central atom
In this step, the outer atoms are joined to the central atom using single straight lines. So, the three outer P-atoms are now joined to the central phosphorus atom in the P4 Lewis structure, as shown below.
Each straight line represents a single covalent bond, i.e., a bonded electron pair containing 2 electrons. There are a total of 3 single bonds in the above diagram; thus, 3(2) = 6 valence electrons.
Total valence electrons available – electrons used till step 3 = 20 – 6 = 14 valence electrons.
This means 14 valence electrons are still available to be accommodated in the Lewis dot structure of P4.
4. Connect adjacent outer P-atoms to each other
The unique step while drawing the P4 Lewis structure is that in addition to joining the outer P-atoms with the central P-atom, the outer atoms are also connected to each other via single covalent bonds.
So, each outer P-atom is joined to its adjacent P-atoms, as shown below.
This results in a three-dimensional ringed structure. All four P-atoms are now equivalent in this Lewis structure, and anyone P-atom can be considered a central atom while determining the shape and geometry of P4.
5. Complete the octet of all four P-atoms
A phosphorus atom needs a total of 8 valence electrons to complete its octet. All four P-atoms in the above Lewis structure have a total of 3 single bonds around them, which denotes 6 valence electrons. Thus, it is short of 2 more electrons in order to achieve a stable octet electronic configuration.
Total valence electrons used till step 4 = 6 single bonds = 6(2) = 12 valence electrons.
Total valence electrons – electrons used till step 4 = 20 – 12 = 8 valence electrons.
The above calculation shows that we still have 8 valence electrons that we can use in the P4 Lewis structure. So, 2 valence electrons are placed around each P-atom as a lone pair.
Now in the above structure, each P-atom has a complete octet with 3 single bonds + 1 lone pair = 3(2) + 2 = 8 electrons. Also, all the 20 valence electrons initially available are finally consumed.
So, the final step is just to check the stability of this Lewis structure. Let us do that using the formal charge concept.
6. Check the stability of the P4 Lewis structure using the formal charge concept
The fewer formal charges present on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
What are the electron and molecular geometry of P4?
The ideal electronic geometry of P4 is tetrahedral. However, the molecular geometry or shape of P4 with respect to any one P-atom is trigonal pyramidal. The presence of a lone pair of electrons on the P-atom makes it adopt a different shape from its ideal electron geometry.
Molecular geometry of P4
The molecular geometry or shape of P4 is trigonal pyramidal. As already discussed, while determining the shape and/or geometry of P4, anyone phosphorus atom can be considered a central atom out of the four P-atoms available. This is because all four P-atoms are identical and equivalent in the tetraphosphorus molecule.
Each P-atom is bonded to three other P-atoms, and it has a lone pair of electrons. Lone pair-bond pair and bond pair-bond pair electronic repulsions exist in the molecule. When noticed three-dimensionally, the three bonded P-atoms form a triangular base, while the lone pair forms a pyramid at the top, as shown below.
One should keep in mind that the molecular geometry or shape of a molecule depends on the different number of lone pairs and bond pairs present around the central atom.
However, the ideal electron geometry of the molecule only depends on the total number of electron density regions or electron domains around the central atom.
Let’s see how this concept applies to the tetraphosphorus (P4) molecule.
Electron geometry of P4
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
Considering any one P-atom as a central atom in P4, it has 3 bond pairs and 1 lone pair around it, which makes a total of 3+1 = 4 electron density regions; thus, the electron geometry of P4 is tetrahedral.
A shortcut to finding the electron and the molecular geometry of a molecule is by using the AXN method.
AXN is a simple formula to represent the number of atoms bonded to the central atom in a molecule and the number of lone pairs present on it.
It is used to predict the shape and geometry of a molecule based on the VSEPR concept.
AXN notation for P4
A in the AXN formula represents the central atom. In P4, a phosphorus (P) atom is present at the center, so A = P for P4.
X denotes the atoms bonded to the central atom. In P4, three P-atoms are bonded to the central phosphorus atom, so X = 3.
N stands for the lone pairs present on the central atom. As per the Lewis structure of P4, one lone pair of electrons is present on the central phosphorus atom, so N = 1.
Hence, the AXN generic formula for P4 is AX3N1or AX3N.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart above confirms that the ideal electron geometry of a molecule with AX3N generic formula is tetrahedral while its molecular geometry is trigonal pyramidal, as we already noted for the tetraphosphorus (P4) molecule.
Hybridization of P4
The P4 molecule has sp3 hybridization with respect to all four P-atoms.
During chemical bonding, one 3s atomic orbital of phosphorus hybridizes with three half-filled 3p orbitals to produce four sp3 hybrid orbitals.
Each sp3 hybrid orbital of phosphorus possesses a 25% s-character and a 75% p-character. One of these four sp3 hybrid orbitals contains paired electrons which are situated as a lone pair on the phosphorus atom in P4.
The other three sp3 hybrid orbitals contain a single electron each which they use for sigma (σ) bond formation by overlapping with the sp3 hybrid orbitals of three adjacent P-atoms, as shown below.
A shortcut to finding the hybridization present in a molecule is by using its steric number against the table given below.
The steric number of a phosphorus atom in P4 is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The P4 bond angle
The ideal bond angle in a tetrahedral molecule is 109.5°.
However, the tetraphosphorus (P4) molecule forms a ringed structure. P-P bonds present in a ringed arrangement experience strong ring strain and, thus, instability.
The presence of a total of 4 lone pairs in this ringed arrangement also leads to a strong electron-repulsive effect. The P-P bonds tilt inwards. Consequently, the P-P-P bond angle decreases from the ideal 109.5° to only 60° in P4.
The P-P bond lengths are approx. 221 pm in the tetraphosphorus (P4) molecule.
According to Pauling’s electronegativity scale, a covalent chemical bond is considered polar if the bonded atoms have an electronegativity difference between 0.5 to 1.6 units.
As P4 consists of four identical phosphorus atoms and the electronegativity value of each phosphorus atom are 2.19 units.
Therefore, a zero electronegativity difference exists between the bonded atoms in each P-P bond in the P4 molecule. Each P-atom pulls the shared P-P electron cloud towards itself to the same extent.
The electron cloud stays uniformly spread over the molecule. Thus, P4 is a non-polar molecule overall (net dipole moment µ = 0).
The Lewis structure for P4 displays a total of 20 valence electrons i.e., 20/2 = 10 electron pairs.
Out of these 10 electron pairs, there are 6 bond pairs and 4 lone pairs of electrons.
Each P-atom is bonded to three adjacent P-atoms via single covalent bonds, and it has a lone pair of electrons.
This results in a three-dimensional ringed arrangement.
How many total bond pairs and lone pairs are there in the P4 Lewis structure?
There are a total of 6 bond pairs and 4 lone pairs in the P4 Lewis structure. Around each P-atom, there are 3 bond pairs and 1 lone pair, respectively.
Why do bonded atoms lie in a ringed tetrahedral arrangement in P4?
A total of only 20 valence electrons are available for drawing the Lewis structure of P4. Each P-atom needs a total of 8 valence electrons to complete its octet configuration.
1 P-P single bond and 3 lone pairs around this P-atom for four P-atoms would exceed the total valence electrons limit.
Therefore, the adjacent P-atoms are joined to each other in a tetrahedral ringed arrangement, and 1 lone pair is placed on top of each to complete its octet.
What is the shape and geometry of P4 as per the VSEPR concept?
As per the VSEPR concept, the AXN generic formula for P4 is AX3N. So it’s ideal electron geometry is tetrahedral, while its molecular geometry or shape is trigonal pyramidal.
Why does the ∠P-P-P bond angle decrease in P4?
The phosphorus atoms are present in a ringed arrangement in P4. Ring strain and the presence of four lone pairs of electrons in this ring decrease the ∠P-P-P bond angle from the ideal 109.5° to about 60°.
Compare the shape of P4 with that of P4O10.
In the P4 molecule, the P-atoms are arranged in a tetrahedral ringed arrangement, while its molecular geometry or shape is trigonal pyramidal.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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