Na3PO4 Lewis Structure & Characteristics (13 Helpful Facts)

Na₃PO₄ or trisodium phosphate is the salt of the phosphoric acid molecule having a molecular weight of 163.939 g/mol. We will discuss Na₃PO₄ in this article in brief.

Na₃PO₄ can be thought of as phosphoric acid where all three H atoms are replaced by the three Na atoms. where Na and O are not involved in the direct bond formation rather they are attached with ionic interaction. The P-O bond is stronger due to double bond and for this reason, the Na-O bond can be cleaved.

Na₃PO₄ is an inorganic strong salt as it is formed from the strong tribasic phosphoric acid. Let us discuss about polarity, lewis structure, hybridization, solubility, bond angle, and molecular shape of the Na₃PO₄ in the following article with proper explanation.

1.  How to draw Na₃PO₄ lewis structure?

The lewis structure of the Na3PO4 can be explained by the octet rule, valency, and simple bond formation. Now we try to draw the structure of Na3PO4.

Counting the total valence electrons

The total valence electrons are counted to be 32 for the Na₃PO₄, and those electrons are coming from the three Na, One P, and four O atoms. So, basically, total valence electrons for a molecule are the summation of the individual atoms’ valence electrons.

Choosing the central atom

The central atom has greater importance in a lewis structure because concerning the central atom other atoms should be connected through the required number of bonds. Based on the electropositivity as well as larger size P is chosen as central atom here. The remaining atoms are present in the surroundings.

Satisfying the octet

The electrons required as per octet are 46 because each s block element needs two electrons and p block eight electrons to complete valence orbital. Here all atoms complete their valence shell by sharing electrons through the covalent bond with each other and satisfying their octet with suitable electrons.

Satisfying the valency

The electrons required for the octet are 46 and the available valence electrons for the molecule are 32, so, the remaining 46-32 = 14 electrons are shared by the 14/2 = 7 bonds. So, a minimum of 7 bonds are required for the Na₃PO₄ structure construction. All the atoms must be connected through those bonds.

Assign the lone pairs

After adding seven electrons if the valency is not completed then the required number of bonds should be added. After that, if there will be excess electrons present then those electrons exist as lone pairs over that particular atom. Here only O has lone pairs, which are present in their valence shell.

2. Na₃PO₄ valence electrons

The total valence electrons for the Na₃PO₄ are the summation of an individual atom’s valence electrons. Let us count the valence electrons for the Na3PO4.

The total number of valence electrons present in the Na₃PO₄ molecule is 32 and those numbers are the summation of the valence electrons for three Na, one P, and for four O atoms. So, the total valence electrons of a molecule is summation of individual atoms’ valence electrons.

• The valence electrons for the Na atom is 1 ([Ne]3s¹)
• The valence electrons for the P atoms are 5 ([Ne]3s²3p³)
• The valence electrons for each O atom are, 6 ([He]2s²2p⁴)
• So, the total valence electrons for the Na3PO4 are, 1+(1*2)+5+(6*4) = 32

3. Na₃PO₄ lewis structure lone pairs

The lone pairs over the Na₃PO₄ are those present in valence orbital but not involved in bonding but participate in the reaction. Let us count lone pairs of Na₃PO₄.

The total lone pairs over the Na₃PO₄ molecule are 16 electrons which means 8 pairs of lone pairs, which are contributed from the four O atoms. Only O contains lone pairs in the Na₃PO₄ molecule because it has more valence electrons than its bonding electrons. Na, H, and P do not have any lone pairs.

• Let us count the lone pairs of the individual atom by the formula, lone pairs = electrons present in the valence orbital – electrons involved in the bond formation
• The lone pairs present over the Na atom is, 1-1 = 0
• The lone pairs present over the P atom is, 5-5 = 0
• The lone pairs present over each Oa tom are, 6-2 = 4
• So, each O contains two pairs of lone pairs and the total number of the lone pairs present in the Na3PO4 molecule is 2*4 = 8 pairs.

4. Na₃PO₄ lewis structure octet rule

Any atom after the bond formation tries to complete its octet by accepting suitable numbers of electrons in the valence orbital. Let us discuss octet of Na₃PO₄.

Na₃PO₄ obeys octet during bond formation because all the atoms are incomplete valence orbital. Na is s block element so it needs two electrons in its valence orbital, where P and O are p block elements so they need eight electrons. During bond formation, the total need for electrons as per octet will be 46.

Each Na forms a single bond with O and shares two electrons

5. Na₃PO₄ lewis structure shape

The molecular shape is determined by the VSEPR and the presence of the central atom and surrounding atom for proper arrangement. Let us predict the shape of Na₃PO₄.

Na₃PO₄ adopted tetrahedral geometry which can be determined by the following table –

Tetrahedral is the best geometry for tetra-coordinated molecules like AX₄ as per VSEPR (Valence Shell Electrons Pair Theory) without having lone pairs over the central atom like Na₃PO₄. P is present at the center of the tetrahedral moiety.

6. Na₃PO₄ lewis structure angle

The bond angle is the angle made by the central atom and other atoms in the adopted geometry for proper orientation. Let us calculate the bond angle for Na₃PO₄.

The bond angle for the Na₃PO₄ molecule around central atom is 109.5⁰. This is ideal value of the bond angle for the tetrahedral molecule and this large bond angle, there is less steric repulsion present within the molecule unlike square planner, where the bond angle is 90⁰ and repulsion will be higher.

• The bond angle value can be calculated by the hybridization value of the central atom.
• The bond angle formula according to Bent’s rule is COSθ = s/(s-1).
• The central atom P is sp³ hybridized, so the s character here is 1/4^th
• So, the bond angle is, COSθ = {(1/4)} / {(1/4)-1} =-( 1/3)
• Θ = COS^-1(-1/3) = 109.5⁰
• So, from the hybridization value, the bond angle for calculated and theoretical value is the same.

7. Na₃PO₄ structure formal charge

The formal charge can predict the charge present over an individual atom in a molecule by assuming equal electronegativity. Let us predict the formal charge of Na₃PO₄.

The formal charge value for the Na₃PO₄ is zero, because the molecule is zero, all the charge carried by the cation is neutralized by the anions. Because they are the same in magnitude but opposite in sign. Although there is a double bond present in the molecule but charged is fully satisfied by the valency.

• The formal charge of the Na3PO4 can be calculated by the formula, F.C. = N_v – N_l.p. -1/2 N_b.p
• The formal charge present over the Na atom is, 1-0-(2/2) = 0
• The formal charge present over the P atom is, 5-0-(10/2) = 0
• The formal charge present over each O atom is, 6-4-(4/2) = 0
• So, the total formal charge present over the molecule is zero.

8. Na₃PO₄ hybridization

To form a new hybrid orbital of equivalent energy central atom undergoes hybridization in covalent bonding. Let us know the hybridization of the Na₃PO₄.

The central P in the Na3PO4 molecule is sp³ hybridized here, which can be determined by the following table –

• We can calculate the hybridization by the convention formula, H = 0.5(V+M-C+A),
• So, the hybridization of central P is, ½(5+3+0+0) = 4 (sp³)
• One s orbital and three p orbitals of P are involved in the hybridization.
• The double bond between P and O is not involved in the hybridization.

9. Na₃PO₄ solubility

The solubility of a molecule in a particular solvent depends on the dissociation of the molecule in that solution. Let us discuss whether Na₃PO₄ is soluble in water or not.

Na₃PO₄ can be soluble in water by the dissociation of the ions and gets soluble in it. The main reason there is an H atom present is it can be involved in the H-bonding formation. Even the P-O bond is not so strong so it can be dissociated into ions when it gets soluble in water.

Na₃PO₄ can be soluble in another solvent like,

• CHCl₃
• CCl₄
• Methanol
• Benzene
• CS₂ (insoluble)

10. Is Na₃PO₄ solid or liquid?

The physical state of a molecule depends on the entropy present in the molecule and the temperature applied. Let us see whether Na₃PO₄ is solid or not.

Na₃PO₄ is a solid white crystal molecule because it contains a hydrated part. In the lattice structure if the hydrated part is present then the lattice becomes stronger and the entropy of the molecule decreases and it can exist as a solid form at room temperature.

11. Is Na₃PO₄ polar or nonpolar?

A molecule is said to be polar if it has a permanent non-zero dipole-moment value and electronegativity difference. Let us see whether Na₃PO₄ is polar or not.

Na₃PO₄ is a polar molecule because it has an asymmetrical structure and for this reason, the dipole moment which flows from the P to O atoms is independent of direction. Four dipole-moment flows are occurring in the molecule but they are in different directions and do not cancel each other, making it polar.

Tetrahedral geometry is not symmetrical around the central tom and the four directions are not equally distributed so, a tetrahedral molecule is always polar.

12. Is Na₃PO₄ acidic or basic?

According to the Arrhenius theory in an aqueous solution releasing H⁺ and OH^– is considered to be acid or base respectively. Let us see whether Na₃PO₄ is acid or not.

Na₃PO₄ is neither acidic nor basic rather it is a salt of phosphoric acid because all the acidic protons in the phosphoric acid are replaced by the Na atoms. As, it forms from the strong acid so it is a strong salt, but due to the vacant orbital of P it can take an electron and behaves as lewis acid.

It is a ternary salt because it can form by the neutralization reaction of three equivalent bases and one tribasic acid. Also, the conjugate base of the molecule is phosphate which has more resonance stabilized.

13. Is Na₃PO₄ electrolyte?

The substance is called electrolyte which can be ionized in the aqueous solution and carry the electricity. Let us see whether Na₃PO₄ is an electrolyte or not.

Na₃PO₄ is a strong electrolyte because when it is dissociated in the aqueous solution then it ionized to Na⁺, and PO₄^3-. All the above particles are highly charged and their mobility is very high so, they can carry electricity in a very faster way. So, it can act as a strong electrolyte in solution.

14. Is Na₃PO₄ ionic or covalent?

On the theory of polarizability by Fajan’s rule we can predict if a molecule is ionic or covalent in nature. Let us check whether Na₃PO₄ is ionic or covalent in nature.

Na3PO4 is a covalent molecule because the central P atom undergoes hybridization to form a proper covalent bond. Also, all the atoms in the molecule make the bond via sharing of electrons equally. Although the bond has slightly polar in character the molecule is covalent according to Fajan’s rule.

Based on the polarizability and the polarizing power it shows a slightly ionic character.

Conclusion

Na₃PO₄ exists in the hydrated form as Na₃PO₄. 12H₂O, due to the presence of water molecules is soluble in water very quickly. Soda ash and zeolites are the substituted product formed from the Na₃PO₄. It is also used in food additives.

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Biswarup Chandra Dey

Hi……I am Biswarup Chandra Dey, I have completed my Master’s in Chemistry from the Central University of Punjab. My area of specialization is Inorganic Chemistry. Chemistry is not all about reading line by line and memorizing, it is a concept to understand in an easy way and here I am sharing with you the concept about chemistry which I learn because knowledge is worth to share it.