PO4 3- Lewis Structure: Drawings, Hybridization, Shape, Charges, Pair and Detailed Facts


PO4 3- is a form of phosphate ion which is a hydrogen phosphate conjugate base.

PO4 3- is a phosphoric acid derivative and one of the form of phosphate ion of phosphorous oxyanion. It is an inorganic trivalent anion. In E.Coli bacteria it is found as metabolite. It is a strong base and hydrolyses in H2O to form basic solution. In this editorial we are learning about PO4 3- lewis structure drawings and detailed facts about it.

How to draw lewis structure for PO4 3-?

Chemical formula for Phosphate ion is PO4 3-.

Molecular weight of PO4 3- is 94.971 g mol-1.

Molecular geometry of PO4 3- is tetrahedral.

PO4 3- has sp3 hybridization.

PO4 3- is non-polar in nature.

In PO4 3- (phosphate ion) there are one phosphorous atom at centre and four outer oxygen atoms are present. All the four oxygen atoms are joined with central phosphorous atom, one oxygen atom is lined with phosphorous by double bonds and other three oxygen atoms linked with single covalent bond also having -1 charge on all this three oxygen atoms. Overall charge on central phosphorous atom has -3 charges and also phosphorous atom is in +5 (O.S) oxidation state.

There are few rules to remember while drawing any lewis structure:

  1. Counting of the structure’s total valence electrons.
  2. Selection for central position the element with lowest electronegativity in structure.
  3. Create bonding between all the atoms existing in structure.

We have to check the position of P and O in the periodic table to count its valence electrons. So as per periodic table P atom comes under 15th group and O atom comes under 16th group of periodic table. Thus, phosphorous and oxygen has five and six valence electrons in its valence shell respectively.

Therefore, Phosphorous total valence electrons = 5×1 (P) = 5

                  Oxygen total valence electrons = 6×4 (O) = 24

Also we have to add more three electrons to count total valence electrons of PO4 3-, as there is a -3 charge present on phosphate ions.

So, PO4 3- lewis structure has total valence electrons = 5 (P) + 24 (O) + 3 (-3) = 32

Now, let we count total valence electron pairs of PO4 3-.

Total valence electron pair (PO4 3-) = sigma (σ) bonds + pi (π) bonds + valence shell lone pair electrons

To count total valence electron pair we have to divide total number of valence electrons by 2.

Hence, total valence electron pair for PO4 3- = 32/2 = 16

Now, choose the atom for central position which has more valence or which is least electronegative in nature. Phosphorous belongs to 15th group and has electronegativity 2.19 also it has maximum valency 5. Oxygen belongs to 16th group and has electronegativity 3.44 also it has maximum valency 2.

So, we can see that P is more electronegative than O also it has more valency too. Therefore, P atom is at central position and all the four O atoms are at corners (outside or surrounds P) of the PO4 3- lewis structure.

PO4 3- structure showing Phosphorous at central position

Now, make bonding between all atoms of PO4 3- ion. Draw four single covalent bonds with four surrounding oxygen atoms. Two valence electrons get involved in one bond. Means total eight valence electrons (four electron bond pairs) get used in bonding of four P-O bonds.

PO4 3- structure showing bonding between P and O

PO4 3- lewis structure octet rule

We have already made four covalent P-O bonds besides P atom in above image by engaging four bond pair electrons from total sixteen valence electrons. Now, we have remaining twelve valence electron pairs for distribution of electrons to complete the octet of P and O atoms.

Now, let’s share these twelve valence electron pairs on outer four oxygen atoms to complete its octet. There will be three lone electron pairs can put on single oxygen atom as oxygen atom cannot take extra electrons rather than eight electrons to in its outer valence shell.

So, all the twelve electron pairs as lone pair electrons get shared between all four oxygen atoms. Thus, no more electron pair get remain to put on phosphorous atom, even phosphorous atom already had eight valence electrons (four bond pairs) in its valence shell to form four P-O bonds and its octet is already complete.

Therefore, central phosphorous atom and all outer four oxygen atoms have complete its octet by sharing 16 electron pairs.

PO4 3- lewis structure showing complete octet of P and O atoms

PO4 3- lewis structure formal charges

Any lewis structure containing low formal charge is the more stable lewis structure. There is a formula to calculate formal charge as follows.

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

Let us calculate the formal charges on central phosphorous atom and outer four oxygen atom of PO4 3- lewis structure.

Phosphorous atom: Valence electron on central phosphorous atom = 05

                                   Lone pair electrons on central phosphorous atom = 00

                                   Bonding electrons around central phosphorous atom = 8 (single 4 bonds with four O)

Phosphorous atom Formal charge = (05 – 0 – 8/2) = +1

Hence, in PO4 3- lewis structure the central phosphorous atom has +1 formal charge.

Oxygen atom: Valence electrons on oxygen = 06

                         Lone pair electrons on oxygen = 06

                         Bonding electrons with oxygen = 2

Oxygen atom Formal charge = (6 – 6 – 2/2) = -1

So, the oxygen atom in PO4 3- lewis structure has -1 formal charge.

Thus, the PO4 3- has +1 formal charge on P atom and -1 formal charge on O atom, this type of lewis structure are not stable structures, so we have to minimize the formal charge on oxygen by changing lone pair electron to bond pair.

PO4 3- lewis structure lone pairs

Sixteen total valence pair electrons are present on PO4 3- structure. Central P atom has four bonds linked to four O atoms in PO4 3- structure. So after four P-O bonds there are only 12 electron pairs get left in PO4 3- ion.

As we already see that oxygen comes under 2nd period of the periodic table and it do not have more the eight electrons in its last outer shell orbital. So, let we mark lone pair electrons on four outer O atoms. Central P atom has no lone electron pair as it already has 4 bond pairs with 4 O atoms.

So, the outer four O atoms of PO4 3- lewis structure has total 12 lone electron pairs, three pairs on each single O atom.

PO4 3- lewis structure shape

In PO4 3- lewis structure, the middle phosphorous atom has four bonds with four oxygen atoms. All the P and 4 O elements are settled in a possible geometric arrangement with each other that can they minimize repulsion within bond pairs of each other.

According to VSEPR theory, any structure or molecule accepts the geometry that minimizes repulsion. Means if there are no lone pair electrons available on any lewis structure then there is no repulsion between bond pairs. The generic formula under VSEPR theory is AX4 which is suitable for PO4 3- lewis structure.

AX4:- A = no. of central atoms

          X = no.of outer bonded atoms

Therefore, according to molecular geometry of PO4 3- ion, the shape of PO4 3- lewis structure is tetrahedral.

PO4 3- Hybridization

Any structures or molecules hybridization is based on its steric number. PO4 3- lewis structures hybridization can be determine by finding the steric number of its central atom phosphorous.

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 PO4 3- = (no. of elements or atoms bonded with phosphorous + phosphorous atom lone electrons pair)

As we see the PO4 3- lewis structure, central phosphorous atom attached with four oxygen atom i.e. four bonds with four oxygen atoms and have no lone electron pairs on phosphorous atoms.

So, PO4 3- steric number = 4 + 0 = 4

In PO4 3- lewis structure, central P atom has a steric number four after calculation, so it has a Sp3 hybridization of phosphorous in PO4 3- ion.

PO4 3- lewis structure resonance

The difference in electron distribution and formation of different bonding in same molecule is its resonance structure. Any resonance structure of any molecule should have multiple double or triple bonds and also there is at least one lone pair electron should be present to get its resonance structure.

Whenever the charge is present in any molecule or ion, then the structure is not consider as a stable structure. To get the stable form of structure we have to minimize the charges on the atoms present in that molecule.

In case of PO4 3- ion, the above same situation we can see as the +1 charge is present on P atom and -1 charges are present on all four O atoms. So, the above PO4 3- structure showing formal charge is unstable in nature. We have to minimize the charges on it to get the stable structure. We can get the two forms of resonance structure of PO4 3- ions as follows.

PO4 3- lewis structure showing two resonance structures

In the above both resonance structure of PO4 3-, O atoms bears negative charges as it has 3.44 electronegativity which is higher than the 2.19 electronegativity of P atom. That’s why; oxygen atoms have a high capacity of carrying negative charge as compared to phosphorous atom.

Above structure (1) is an unstable resonance structure as all oxygen atoms bearing -1 negative charge. So, we have to decrease the negative charges by transforming lone electron pairs to form a bond. Therefore, one lone electron pair from one O atom get converted to form another P-O bond.

Hence, in above structure (2) there is the formation of one double bond (P=O) within one P atom and one O atom. So, PO4 3- lewis structure now has three single covalent (P-O) bonds within one P atom and three O atoms. Thus, the second resonance structure shows a stable form of PO4 3- lewis structure.

PO4 3- polar or nonpolar

The main reason behind polarity occurs in any molecule or ion is its electronegativity difference. There is a non-zero dipole moment and have asymmetrical shape in polar molecules.

The electronegativity of P atom is 2.19 and electronegativity of O atom is 3.44 and its difference is 1.25 which is greater than Pauling’s rule value 0.5 making polar P-O bond.

But if we draw a dipole moments in PO4 3- lewis structure for each bond. As the PO4 3- molecule has a symmetrical structure, due to which the dipole moments cancel one another making PO4 3- a non-polar molecule.

For the conformation of non-polar nature of PO4 3- ion, we can see its molecular geometry as it has a tetrahedral shape and its each dipole moment goes in opposite direction and has the zero net dipole moment which confirms the non-polar nature of PO4 3- molecule.

PO4 3- lewis structure bond angle

The molecular geometry of PO4 3- ion shows tetrahedral shape with VSEPR generic formula AX4, it shows that in the PO4 3- lewis structure the central P atom attached to outer four O atoms.

So, the PO4 3- lewis structure has the 109.5 degree bond angle.

PO4 3- lewis structure showing bond angle

PO4 3- Uses

  • Phosphate ions are used in home maintenance as treatment products in septic systems.
  • Phosphate ion is used as active substance in manufacturing and commercial activities.
  • Phosphate ions are used in landscaping and yards and inside home for various household purposes.
  • Phosphate ions are used as fertilizers in farming.
  • Phosphate ions also used as fire retarder.
  • Phosphate ions are used in various personal care and pharmaceutical products like bath soaps and bars, shower gels, body cleanser, washes, contact lenses cleaning solutions, etc.
  • Phosphate ions are used in the personal care creams to get relief from insects bite.
  • Phosphate ions are used in various polishing agents and in toothpaste.

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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