NaH2PO4 Structure & Characteristics (13 Helpful Facts)


NaH2PO4 or monosodium phosphate is the dibasic acid of P having a molecular weight of 119.98 g/mol. This article contains information regarding NaH2PO4.

NaH2PO4 is the binary acid molecule of the P atom. P makes one double bond with O and three single bonds to complete the octet. The counter anion phosphate is resonance stabilized and for this reason, it is a strong acid. It is also known as sodium dihydrogen phosphate and is used for the detection of Mg.

Sodium acid pyrophosphate can be prepared by heating this molecule above 1500 C. The molecular property, hybridization, shape, angle, and polarity of the monosodium phosphate should be discussed with proper explanation in the following part of the article.

1.     How to draw NaH2PO4 structure?

The lewis structure of the NaH2PO4 can be explained by the octet rule, valency, and simple bond formation. Now we try to draw the structure of NaH2PO4.

Counting the total valence electrons

The total valence electrons are counted to be 32 for the NaH2PO4, and those electrons are coming from the one Na, two H, 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 electropositivity as well as larger size P is chosen as the 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 the atoms complete their valence shell by sharing electron 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 NaH2PO4 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.

NaH2PO4 Lewis structure

2.     NaH2PO4 valence electrons

The total valence electrons for the NaH2PO4 are the summation of an individual atom’s valence electrons. Let us count the valence electrons for the NaH2PO4.

The total number of valence electrons present in the NaH2PO4 molecule is 32 and those numbers are the summation of the valence electrons for two H, one NA, one P, and for four O atoms. So, the total valence electrons of a molecule just counted the individual atom’s valence electrons and added them together.

  • The valence electrons for the H atom is 1 (1s1)
  • 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 NaH2PO4 are, 1+(1*2)+5+(6*4) = 32

3.     NaH2PO4 structure lone pairs

The lone pairs over the NaH2PO4 are those present in valence orbital but not involved in bonding but participate in the reaction. Let us count lone pairs of NaH2PO4.

The total lone pairs over the NaH2PO4 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 NaH2PO4 molecule because it has more valence electron 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 over the H atom is, 1-1 = 0
  • 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 NaH2PO4 molecule is 2*4 = 8 pairs.

4.     NaH2PO4 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 NaH2PO4.

NaH2PO4 adopted tetrahedral geometry which can be determined by the following table.

Molecular
Formula
No. of
bond pairs
No. of
lone pairs
Shape  Geometry    
AX10Linear  Linear
AX2        20Linear  Linear  
AXE       11Linear  Linear  
AX330Trigonal
planar
Trigonal
Planar
AX2E     21BentTrigonal
Planar
AXE2     12Linear  Trigonal
Planar
AX440TetrahedralTetrahedral
AX3E     31Trigonal
pyramidal        
Tetrahedral
AX2E2                2BentTetrahedral
AXE3                     13Linear  Tetrahedral
AX550trigonal
bipyramidal
trigonal
bipyramidal
AX4E     41seesawtrigonal
bipyramidal
AX3E2    32t-shaped         trigonal
bipyramidal
AX2E3    23linear   trigonal
bipyramidal
AX660octahedraloctahedral
AX5E     51             square
pyramidal   
octahedral
AX4E2                    42square
pyramidal 
octahedral
VSEPR Table
NaH2PO4 Molecular Shape

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 NaH2PO4. P is present at the center of the tetrahedral moiety.

5.     NaH2PO4 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 NaH2PO4.

The bond angle for the NaH2PO4 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.

NaH2PO4 Bond Angle
  • 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 1/4th
  • 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.

6.     NaH2PO4 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 NaH2PO4.

The formal charge value for the NaH2PO4 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 NaH2PO4 can be calculated by the formula, F.C. = Nv – Nl.p. -1/2 Nb.p
  • The formal charge present over the Na atom is, 1-0-(2/2) = 0
  • The formal charge present over the H 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.

7.     NaH2PO4 hybridization

To form a new hybrid orbital of equivalent energy central atom undergoes hybridization in covalent bonding. Let us know the hybridization of the NaH2PO4.

The central P in the NaH2PO4 molecule is sp3 hybridized, which can be determined by the following table.

Structure   Hybridization
value  
State of
hybridization
of central atom
Bond angle
1.Linear         2         sp /sd / pd1800
2.Planner
trigonal      
3sp2                   1200
3.Tetrahedral 4sd3/ sp3109.50
4.Trigonal
bipyramidal
5sp3d/dsp3900 (axial),
1200(equatorial)
5.Octahedral   6        sp3d2/ d2sp3900
6.Pentagonal
bipyramidal
7sp3d3/d3sp3900,720
Hybridization Table
NaH2PO4 Hybridization
  • 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.

8.     NaH2PO4 solubility

The solubility of a molecule in a particular solvent depends on the dissociation of the molecule in that solution. Let us discuss whether NaH2PO4 is soluble in water or not.

NaH2PO4 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 its gets soluble in water.

NaH2PO4 can be soluble in another solvent like

  • CHCl3
  • CCl4
  • Methanol
  • benzene

9.     Is NaH2PO4 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 NaH2Po4 is solid or not.

NaH2PO4 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.

Actually, the higher the entropy higher will be the randomness of the atoms, and the higher will be the chance to stay in gaseous form.

10. Is NaH2PO4 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 NaH2PO4 is polar or not.

NaH2PO4 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 atom and the four directions are not equally distributed so, a tetrahedral molecule is always polar.

11. Is NaH2PO4 acidic or basic?

According to the Arrhenius theory in an aqueous solution releasing H+ and OHis considered to be acid or base respectively. Let us see whether NaH2PO4 is acid or not.

NaH2PO4 is an acid because it has an acidic proton in it. The H atoms are attached to electronegative O atoms and for this reason, O can pull the electron density of the bond and the O-H bond becomes weaker and easily cleaved. Releasing H+ is very easy for this molecule and behaves as an acid.

It is a dibasic acid because it can neutralize two equivalent bases and has two acidic protons. Also, the conjugate base of the molecule is phosphate which has more resonance stabilized so the corresponding acid will be stronger.

12. Is NaH2PO4 electrolyte?

The substance is called electrolyte which can be ionized in the aqueous solution and carry the electricity. Let us see whether NaH2PO4 is an electrolyte or not.

NaH2PO4 is a strong electrolyte because when it is dissociated in the aqueous solution, it is ionized to H+, Na+, and PO43-. 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.

13. Is NaH2PO4 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 NaH2PO4 is ionic or covalent in nature.

NaH2PO4 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

NaH2PO4 is a dibasic acid due to two acidic protons the acidic nature of the molecule is very strong. It can also be used as an oxidizing agent and it can oxidize many compounds. It is used in toothpaste and even evaporated milk.

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Biswarup Chandra Dey

Hi......I am Biswarup Chandra Dey, I have completed my Master's in Chemistry. 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.

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