Trisodium phosphate Lewis Structure

Trisodium phosphate Lewis Structure: Na₃O₄P Lewis Structure, tetrahedral Geometry, sp3 Hybridization & Polarity

Trisodium phosphate Key Facts

The Trisodium phosphate Lewis structure is P–O single bond, P–O double bond, P–O single bond and P–O single bond; the central P has 4 electron domains (0 lone pairs), giving a tetrahedral electron-domain arrangement and a tetrahedral molecular geometry with a 109.5° bond angle. P is best described as sp3-hybridized, and Trisodium phosphate is nonpolar because the bond dipoles cancel by molecular symmetry.

Figure 1: Lewis Structure of Trisodium phosphate (Na₃O₄P)

Chemical Formula	Na₃O₄P
CAS Number	7601-54-9
Total Valence Electrons	32
Lewis Structure	P–O single bond, P–O double bond, P–O single bond and P–O single bond
Electron-Domain Geometry	tetrahedral
Molecular Geometry	tetrahedral
Hybridization Model	sp3 (central P)
Bond Angle	109.5°
Polarity	Nonpolar molecule

PubChem (CID 24243) and NIST list Trisodium phosphate as Na ₃O ₄P with CAS 7601-54-9; molecular weight ≈ 163.941 g/mol. View CAS 7601-54-9 dictionary details on Guidechem →

Applications of Trisodium phosphate (CAS 7601-54-9)

The P oxide Trisodium phosphate is a key industrial intermediate. Nonmetal oxides such as SO₃ and P₄O₁₀ are acid anhydrides for sulfuric and phosphoric acid manufacture, while metal/semimetal oxides are ceramics, refractories, catalysts and pigment precursors.

Acid Anhydride / Intermediate Gateway to the corresponding oxoacid and its salts (fertilizers, detergents).

Materials & Catalysis Oxide ceramics, refractories, catalysts and pigment feedstocks.

Process Gas / Reagent Oxidizing or reactive reagent in inorganic and environmental processing.

Procurement Note "Trisodium phosphate" is supplied in multiple commercial grades and package sizes. Specify purity, grade, moisture/impurity limits, package (cylinder, drum or bulk) and intended process, and use CAS 7601-54-9 as the primary identifier when screening suppliers; always confirm regional availability and safety documentation (SDS).

Step 1 - Valence Electrons & Central Atom

To draw the Trisodium phosphate Lewis structure we first count the total valence electrons. Na₃O₄P contains 3×1 (Na) + 4×6 (O) + 5 (P); the net charge of 0 gives a total of 32 valence electrons to place.

The central atom is P. It is the least electronegative atom capable of forming multiple bonds and is surrounded by the more electronegative terminal atom(s); hydrogen, when present, always occupies a terminal position. Electronegativity considerations place the electron density toward the terminal atom(s).

Valence-electron count

Total valence electrons = 3×1 (Na) + 4×6 (O) + 5 (P) = 32 electrons.

Step 2 - Lewis Structure & Electron Distribution

Place P at the center and connect each surrounding atom with a single bond, complete octets on the terminal atoms, and place any remaining electrons on the central atom. The resulting electron distribution is: P–O single bond, P–O double bond, P–O single bond and P–O single bond; no lone pairs on P.

Counting bonding and nonbonding electrons around P therefore satisfies the octet/expanded-octet requirement for the drawn structure.

This species is best represented by resonance structures; the π bonding is delocalized over the equivalent terminal atom(s), so all P–terminals bonds are equivalent in the resonance hybrid.

P–O P=O P–O P–O

P: 0 lone pairs, 4 bonding domains

4 bonding domains + 0 lone pairs = 4 electron domains

Octet Rule: Why P Has Eight Electrons P forms 4 bond(s) and retains 0 nonbonding electron(s), reaching an octet. No expanded octet is required for this second-row (or octet-satisfying) central atom.

Step 3 - VSEPR Theory & Geometry

VSEPR theory states that the 4 electron domains around P arrange to minimize mutual repulsion, giving an tetrahedral electron-domain geometry.

Because 0 of these domains are lone pair(s) — and lone pairs repel more strongly than bonding pairs — the observed molecular geometry is tetrahedral; the P bond angle is set to 109.5° rather than the ideal value for the electron-domain geometry.

Repulsion hierarchy

A useful VSEPR approximation is: lone pair–lone pair repulsion > lone pair–bonding pair repulsion > bonding pair–bonding pair repulsion. With 0 lone pair(s) on P, the lone-pair domains occupy positions that minimize overall repulsion while pushing the bonding domains (and therefore the bonded atoms) closer together.

Hybridization & Formal Charge

In the conventional localized-bond model, P uses sp3 hybrid orbitals to form the 4 equivalent electron-domain directions (4 bonding + 0 lone pair).

Formal-charge check

Formal charge on central P = V − N − ½B = 5 − 0 − ½×10 = 0. The preferred Lewis structure carries zero formal charge on the central atom (and on the terminals), so it is the dominant contributor.

Modeling Note Modeling Note: sp3 is a compact model for the 4 electron-domain directions around P; full quantum-chemical treatments use molecular orbitals.

Is Trisodium phosphate Polar or Nonpolar?

Trisodium phosphate is nonpolar. Although individual P–terminal bonds are polar when the atoms differ in electronegativity, the tetrahedral geometry makes their vector sum zero, so there is no net molecular dipole.

Expert Quote — Structural Chemistry Perspective

A common misconception is that polar bonds guarantee a polar molecule. Trisodium phosphate shows the opposite: identical bond dipoles arranged with tetrahedral symmetry cancel exactly, yielding a nonpolar species.

Interpretation consistent with standard VSEPR / molecular-geometry references.

Its nonpolar character governs solvation and intermolecular behavior; specify grade and handling when sourcing.

Structural Comparison Table

Species	Formula	Central Atom	Electron Domains	Molecular Geometry	Polarity
Trisodium phosphate	Na₃O₄P	P	4	tetrahedral	Nonpolar
Phosphine	H₃P	P	4	trigonal pyramidal	Polar
Phosphorus trichloride	Cl₃P	P	4	trigonal pyramidal	Polar
Phosphorus pentachloride	Cl₅P	P	5	trigonal bipyramidal	Nonpolar
Phosphorus trifluoride	F₃P	P	4	trigonal pyramidal	Polar
Phosphorus pentafluoride	F₅P	P	5	trigonal bipyramidal	Nonpolar

Practice question Starting from the 32 valence electrons of Na₃O₄P, draw the Lewis structure and confirm the central P atom is sp3-hybridized with tetrahedral geometry. What happens to the bond angle if one terminal atom is replaced by a more electronegative substituent?

Looking for industrial bulk or specified-grade supplies of Trisodium phosphate (CAS 7601-54-9)? Browse Supplier on Guidechem →

FAQs

Is Na₃O₄P polar or nonpolar?

Trisodium phosphate is nonpolar. Its tetrahedral symmetry cancels the bond dipoles exactly.

What is the Lewis structure of Trisodium phosphate?

P–O single bond, P–O double bond, P–O single bond and P–O single bond; no lone pairs on P. It uses all 32 valence electrons and the preferred structure carries zero formal charge on the central atom.

What is the bond angle in Trisodium phosphate?

The P angle is about 109.5°. Lone-pair repulsion compresses the angle from the ideal tetrahedral value.

What is the hybridization of P in Trisodium phosphate?

The conventional model is sp3. Trisodium phosphate has 4 electron domains around the central P.

What is the CAS number of Trisodium phosphate?

The CAS number is 7601-54-9. PubChem (CID 24243) and NIST identify this with Na₃O₄P; use it to locate suppliers and database records.

References

PubChem CID 24243, Trisodium phosphate. Molecular formula, CAS number, molecular weight and chemical identity.
NIST Chemistry WebBook, SRD 69, Trisodium phosphate. Formula, CAS Registry Number and thermochemical / spectroscopic data.
IUPAC Gold Book. Definitions for "lone pair", "VSEPR", "hybridization" and "formal charge".
Atkins, P. & de Paula, J., Physical Chemistry. VSEPR, molecular geometry and dipole moments.
Guidechem supplier & dictionary records. Commercial sourcing and CAS-linked property pages for Trisodium phosphate (CAS 7601-54-9).

Technical scope: Lewis structures, VSEPR and hybridization are model-based descriptions for chemical communication and structure prediction; actual molecular electronic structure is more accurately represented by molecular-orbital and quantum-chemical methods. Commercial grades vary substantially by supplier and intended use; CAS 7601-54-9 identifies the substance, not a universal purity specification.

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Trisodium phosphate Lewis Structure