PI5 Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair and Detailed Facts


PI5 has full name Phosphorous pentaiodide and it comes under inorganic compounds.

In this article we are discussing about the phosphorous pentaiodide-PI5 lewis structure. As per the theory it consider that the PI5 molecule does not exist as the size of iodide atom is much large and it cannot be put up round phosphorous due to which the P-I bonds becomes weak and prefer to form PI3 molecule.

How to draw lewis structure for PI5?

To draw the lewis structure of any chemical compounds, there are some rules. To calculate the valence electrons of every atom or element present in the chemical compound. If there is ionic compound then count its charges present on it.

After the bonding forms between the atoms distribute the valence electron pairs to every atom until complete its octet means each element or atom should have eight electrons in its outermost orbit. It has some exceptions as hydrogen has just two electrons in its outermost shell. If the compound has multiple bonds (double/ triple bonds), it can formed only some elements like O, N, S, P, C and Cl.

Chemical formula for Phosphorous pentaiodide is PI5.

Molecular weight of PI5 is 665.4961 g mol-1.

Molecular geometry of PI5 is trigonal bipyramidal.

PI5 has sp3d hybridization.

PI5 is non-polar in nature.

Phosphorous pentaiodide (PI5) is composed of two atoms i.e. phosphorous and iodide. The compound has one phosphorous atom and five iodide atoms present in its PI5 lewis structure. PI5 lewis structure shows five single covalent bonds attached to five iodide atoms. There five covalent bonds contains total ten bonding electrons, two electrons present in each single covalent bond and total thirty non-bonding electrons in PI5 structure.

To draw the PI5 lewis structure or diagram, first we have to calculate the total number of valence electrons present on PI5 molecule. Now, calculate the valence electrons on every atom present in PI5 structure i.e. valence electrons present on one phosphorous and five iodide atoms present in PI5 molecule.

To count the valence electrons of any element just check its position in the groups of periodic table. As the phosphorous atom is present on fifteenth group of periodic table and iodide element is on seventeenth group of the periodic table. Therefore, phosphorous atom has five valence electrons and iodine atom has seven valence electrons present on it.

Hence, Total valence electrons on phosphorous = 5

             Total valence electrons on iodine = 7

So, total valence electrons for PI5 lewis structure = 5 (P) + 7×5 (I5) = 40

PI5 lewis structure showing valence electrons

Secondly we have to choose the element with lowest electronegativity of the PI5 molecule. Now, place the element with least electronegativity at the central position to draw the lewis structure because they can more readily share its electrons with the surrounding neighbouring atoms or elements.

In this PI5 molecule, phosphorous atom has electronegativity 2.19 and iodine atom has electronegativity 2.66. We can see that phosphorous atom has low electronegativity than iodine atom. So, the phosphorous atom goes to the central position in PI5 lewis structure surrounded by five iodine atoms.

Third rule is to form connection between all the elements present in the structure by bonding with each other. For that we have to draw the single P-I bonds between one phosphorous and five iodine atoms to connect them with each other i.e. draw five single covalent bonds between central phosphorous and all five iodine atoms.

Now we have to count the valence electrons of below PI5 lewis structure. One single P-I covalent bond contains two electrons. In PI5 lewis structure, there are five single covalent bonds. As the PI5 molecule has total forty valence electrons, ten electrons get consumed to form five single covalent bonds in PI5 lewis structure.

Hence, 40 – 10 = 30 valence electrons

So, PI5 molecule has more 30 electrons left for bonding in PI5 lewis structure.

PI5 lewis structure forming single bonds between phosphorous and iodine

Now we have to count total lone electron pairs. As we have total valence electrons 40 and if this value gets divided by 2 to count total lone pair electrons, we get.

Total lone electron pairs = total no. of valence electrons ÷ 2

Hence, total lone electronpairs = 40 ÷ 2 = 20

PI5 lewis structure octet rule

Octet rule means to fill the outermost shell of any atom with electrons. Here in PI5 lewis structure octet rule apply for the completion of outermost shell of outer elements or atoms with eight electrons i.e. iodine is the outer element of PI5.

So, PI5 lewis structure has iodine as outer elements and we have to fill its outer shell with eight electrons to complete the octet of five iodine atoms.

In PI5 lewis structure, phosphorous is at central position forming five P-I covalent bonds i.e. it has ten electrons filled in its outer shell rather than eight electrons. So, phosphorous has extended octet due to which the PI5 molecule comes under hypervalent molecules.

Now, the all the remaining valence electrons get shared between five iodine atoms until it has eight electrons in its outer shell to complete its octet.

So, PI5 lewis structure has total forty valence electrons from which ten electrons is on central phosphorous atom as five bonding pairs with five iodine atoms. Now, the thirty valence electrons left which means 15 lone electron pairs which get shared with five iodine atoms means three lone electron pair on each iodine atom.

POCl3 lewis structure showing octet

Hence we can see in above structure that the five iodine atoms of PI5 lewis structure gets complete its octet they all have eight electrons in there valence shell. (six electrons on iodine atoms represented by dots and five single bonds with phosphorous containing two electrons)

So, from this we can conclude that the PI5 lewis structure not obeys octet rule because the central phosphorous atom has extended octet (ten electrons) and due to which the PI5 molecule comes under hypervalent molecules.

PI5 lewis structure formal charges

If the atoms in any lewis structure have low formal charges then the lewis structure diagram is more stable. The formula to calculate any atoms formal charge in lewis diagram is as follows:

Formal charge = (valence electrons – lone pair of electrons – ½ bonding electrons)

First calculate the formal charges on all five iodine atoms of PI5 lewis structure. All five iodine atoms have same lone pair and bond pair electrons, so we can calculate the formal charge for one iodine atom also.

Iodine atom: Valence electrons on iodine = 07

                       Lone pair electrons on iodine = 06

                       Bonding electrons with iodine = 2 (one single bond)

Formal charge on iodine = (7 – 6 – 2/2) = 0

So, all the five iodine atoms have zero formal charges.

Phosphorous atom: Valence electron on central phosphorous atom = 05

                          Lone pair electrons on central phosphorous atom = 00

                          Bonding electrons around central phosphorous atom =10 (single 5 bonds)

Formal charge on phosphorous = (05 – 0 – 10/2) = 0

Hence, the central phosphorous atom of PI5 lewis structure has zero formal charge.

PI5 lewis structure lone pairs

From the PI5 lewis structure, assumed that outer single iodine atom has 6 lone electron pairs, so all the five iodine atom has total 30 lone electron pairs present on it. Also central phosphorous atom of PI5 lewis structure has no lone electron pair in its valence shell.

As we said earlier that phosphorous is not obeying octet rule as it is hypervalent in nature because of its extended octet and having 5 P-I bonds with iodine that means ten bonding electrons.

Therefore, PI5 lewis structure has (6×5) I + (0) P = 30 lone electron pairs. So, calculated 30 lone pairs of electrons are present on PI5 lewis structure.

PI5 lewis structure shape

The shape of PI5 lewis structure is trigonal bipyrimidal according to its molecular geometry. PI5 forms trigonal bipyrimidal shape as the central phosphorus atom has 5 bond pairs. According to VSEPR theory, in any lewis structure bond pair electrons of any atom has no repulsion if there are lone pair electrons are not present. Generic formula given by VSEPR theory for PI5 molecule is AX5N0.

As the central phosphorous atom of PI5 lewis structure has five sections of density of electrons i.e. only five bond pairs of electron and no lone pair of electrons.

So PI5 has trigonal bipyrimidal molecular geometry and square pyrimidal electron geometry due to 90 degree bond angle.

PI5 Hybridization

Steric number is a base to find the hybridization of any structure or molecule. PI5 lewis structure hybridization can be assigned by its central phosphorous atoms steric number.

Steric number is the sum of total number of bonded atoms linked (attached) with central atom and lone pair of electrons present on it.

Steric number of PI5 = (no. of bonded elements or atoms attached with phosphorous + phosphorous atom lone pair of electrons)

As we see the PI5 lewis structure above, phosphorous atom joined with five iodine atoms have no lone electron pairs on it.

So, PI5 steric number = 5 + 0 = 5

PI5 lewis structure has a five steric number after calculation, so it is in sp3d hybridization of phosphorous in PI5 structure.

PI5 lewis structure resonance

Resonance structure shows the variation in electron distribution from one structure to another structure. There are some rules to draw the resonance structure for any chemical compound or molecule or for lewis structure. The molecule of structure needed multiple bonds (double/ triple bond) and at least one lone electron pair should be on adjacent atom in the structure.

If any structure have fulfilled this conditions, so we can easily draw resonance structure of any molecule with distribution of electrons and charges on atoms in the molecule. If you would like to draw the PI5 resonance structure, so it is impossible to draw the resonance structure of PI5 molecule because there is no any formal charge on PI5 molecule and also it does not contain any double or triple bond in PI5 lewis structure.

There is a zero formal charge on PI5 molecule and central phosphorous atom have five single covalent bonds joined with five iodine atoms. Also central phosphorous has extended octet but iodine atoms has complete octet in PI5 lewis structure. That’s why PI5 molecule is a stable molecule that cannot form any resonance hybrid structure.

PI5 polar or nonpolar

PI5 lewis structure is non-polar in nature as it has trigonal bipyrimidal geometrical shape. Due to this trigonal bipyrimidal shape of PI5 molecule there is some net dipole moment on it. Also there is a very large electronegativity difference of phosphorous and iodine so P-I bond should also be non-polar in nature. That’s why a PI5 molecule consider as a non-polar molecule.

2.66 is the electronegativity of iodine and 2.19 is the electronegativity of phosphorous. So, the electronegativity difference between phosphorous and iodine atom is 0.47. According to Pauling’s scale for electronegativity, the compound is non-polar in nature if the electronegativity difference between its elements is less than 0.5. So, PI5 comes under non-polar molecules.

Also the PI5 molecule has symmetrical geometry and trigonal bipyrimidal shape and the polar bonds get destroy by cancelling out each other and also there is no existence of opposite charges on this molecule which makes it non polar.

As the iodine is more electronegative than phosphorous atom can cause small negative charge on iodine and small positive charge on phosphorous this creates a dipole moment and this dipole is quite big due to high electronegativity difference between I and P. So for all this reasons PI5 molecule is non-polar in nature as it has equal or symmetrical distribution of polar bonds.

PI5 lewis structure bond angle

The central phosphorous atom of PI5 lewis structure having no lone pair electrons but have five bonding electron pairs i.e. it has 5 electron density sections. Even its molecular geometry shows its trigonal bipyrimidal shape. So its coordination number is five as it has 5 single P-I bonds and also it has D3h point group.

That’s why PI5 has 90 degree or 120 degree bond angle in its trigonal bipyrimidal shape.

PI5 Uses

There is no history on uses of PI5 chemical compound as it cannot exist. As the size of iodine is very high and it cannot put up around the P atom even the P-I bond becomes weak so it is difficult the formation of PI5 compound and it has no uses in any field.

Dr. Shruti Ramteke

Hello everyone I am Dr. Shruti M Ramteke, i did my Ph.D in chemistry. I have five years of teaching experience for 11-12 standard, B,Sc and MSc in chemistry subject. I have published total five research articles during Ph.D on my research work and i have fellowship from UGC for my Ph.D. My Masters with specilization Inorganic chemistry and my graduation with chemistry, zoology and environmental science subjects. thank You

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