Na2SO3 Lewis Structure & Characteristics (13 Helpful Facts)

Na2SO3 or sodium sulfite is a white solid inorganic compound with molar mass 126.043 g/mol. Let us discuss the structure and some important characteristics on Na2SO3 briefly.

Na2SO3 is an ionic compound with hexagonal monoclinic crystal structure. The anhydrous Na2SO3 has density 2.633 g/cm3 whereas the heptahydrate Na2SO3 possesses a density 1.561 g/cm3. Though it has a sharp melting point 33.40C (heptahydrate Na2SO3) and 5000 C (anhydrous) but it has no actual boiling point.

Let us explore the lewis structure, hybridization, bond angle, polarity with some other relevant topics onNa2SO3 in detail.

How to draw Na2SO3 lewis structure?

Lewis structure gives an overall idea of the position of the each of the constituent atom in a molecule. Let us talk about this in detail.

Assigning the valence shell electrons:

The constituent atoms of Na2SO3, sodium (Na), sulfur (S) and oxygen (O) have one, six and six electrons in their respective outer most shell.

Determining the bonding electrons:

There are four covalent bonds present in the SO32- moiety. Therefore, (4×2) = 8 electrons of SO32- are involved in bond formation. Two Na+ atoms donate their two valence electrons to SO32- and generate an ionic interaction.

Finding out the nonbonding electrons:

Sulfur has two, negatively charged oxygen atom has six and neutral oxygen has four nonbonding electrons left in their valence shell.

na2so3 lewis structure
Na2SO3 Lewis Structure

Na2SO3 Lewis Structure Shape

Lewis structure shape of molecule is determined to get an idea on its three-dimensional rearrangement of the atoms. Let us determine its structure.

The shape of the Na2SO3 crystal is hexagonal monoclinic. It is an ionic compound, therefore we cannot determine the lewis structure shape of the whole Na2SO3 molecule. SO32- moiety contains a group of atoms which are attached through covalent bonds. So, the shape of SO32- is trigonal pyramidal.

The shape of SO32- can be predicted from the VSEPR (valence shell electron pair repulsion) theory. Since the central atom of SO32-, sulfur has lone pairs and it faces repulsion from the lone pairs of oxygen, the shape of SO32- is distorted from its molecular geometry (tetrahedral) and shows trigonal pyramidal shape.

Na2SO3 Lewis Structure Formal Charge

Formal charge is known as fake charge or theoretical charge, which is carried by the individual atom in the molecule. Let us calculate the formal charge of the atoms of Na2SO3.

The calculation of formal charge of Na2SO3, an ionic compound is not possible. We can only calculate the formal charge of SO32- (Covalently bonded group of atoms) by using the formula = {Total number of valance electrons – number of nonbonding electrons– (number of bonding electrons /2)}.

  • Formal charge of sulfur = 6 – 2 – (8/2) = 0
  • Formal charge of the oxygen attached through single bond with sulfur = 6 – 6 – (2/2) = -1
  • Formal charge of the oxygen atom attached through double bond with sulfur = 6 – 4 – (4/2) = 0
  • Therefore, the total charge of SO32-= {2× (-1)} = -2.

Na2SO3 Lewis Structure Angle

Bond angle is the angle created between two covalent bonds and one atom in a molecule. Let us find out the bond angle in Na2SO3.

The bond angle of Na2SO3 cannot be determined as it is an ionic compound. There is no covalent bond present between Na+ and SO32-. But we can predict the bond angle in SO32- which is 107.50 from the hybridization (sp3) of it.

Due to presence of lone pair in the central atom, sulfur, the interference of this lone pair (repulsion with the lone pair of oxygen atom) causes a distortion of bond angle from the ideal bond angle (109.50). Therefore, it shows slightly lesser bond angle from ideal case.

Na2SO3 Lewis Structure Octet Rule

Octet rule, a rule of chemistry, depicts that any atom in a molecule tends to gain eight electrons in its valence shell like its nearest inert gas. Let us comment on it.

Na2SO3 obeys octet rule as all of its constituent atoms (except sulfur) satisfy octet rule. Na contains 11 valence electrons and after donating one electron, it attains 8 electrons in its valence shell (2s2 2p6) and matches with the electron configuration of its nearest noble gas, neon.

Sulfur has six outer shell electrons and when it forms 4 covalent bonds with 3 oxygen atoms (3 sigma and one pi), it cannot get eight electrons in its valence shell. Oxygen has six valence electrons and when it forms bond with sulfur atom, it achieves 8 valence shell electron configuration and octet rule is satisfied.

Na2SO3 Lewis Structure Lone Pairs

Lone pairs indicate those valence shell electrons which are not involved in bond formation with the substituent atoms in a molecule. Let us comment on this.

Na2SO3 has total 18 nonbonding electrons or 9 lone pairs which are possessed by the SO32-. The number of lone pairs is calculated using this formula = (Total number of electrons in valence shell – number of bonding electrons).

  • Nonbonding electrons of each of the Na atom = 1 – 1 = 0
  • Nonbonding electrons of sulfur = 6 – 4 = 2
  • Nonbonding electrons of each of the oxygen atom (attached through single bond with sulfur) = 6 – 0 = 6
  • Nonbonding electrons of oxygen bonded with double covalent bond = 6 – 2 = 4.
  • Therefore, total number of nonbonding electrons in Na2SO3 = {2 + (6×2) + 4} = 18 or 9 lone pairs.

Na2SO3 Valence Electrons

Outer most shell electrons of any atom are regarded as valence shell electrons and they contribute in bonding due to having greater reactivity. Let us discuss this.

The total number of valence shell electrons in sodium sulfite (Na2SO3) is 25. These valence electrons are calculated from the summation of the constituent atoms of the molecule. Sodium (Na), sulfur (S) and oxygen (O) have one and six and six electrons in their outer most shell respectively.

Valence electrons are counted from the electron configuration of each atom. Na, S and O have valence shell electron configuration3s1, 3s2 3p4, 2s2 2p4 respectively. Therefore, total number of valence electrons in Na2SO3 is = {1 + 6 + (3×6)} = 25.

Na2SO3 Hybridization

Orbital hybridization is defined as the mixing of two atomic orbitals to generate a new hybrid orbital and the new one is completely different from its atomic orbitals. Let us explore this.

The hybridization of Na2SO3 cannot be determined as it is an ionic compound. The term “hybridization” is only applicable for covalently bonded molecule. For example, in Na2SO3, the hybridization of SO32- can be determined as it is a covalent ionic moiety. The hybridization of SO32- sp3.

Hybridization of any molecule can be determined from the calculation of steric number and the formula is = (Number of lone pairs in central atom – Number of atoms bonded with central atom). Therefore, the steric number of SO32- = 1 + 3 = 4 and hybridization is sp3.

Na2SO3 Solubility

Solubility is defined as the ability of a solute molecule to form solution with a solvent molecule. Let us determine this.

Na2SO3 becomes soluble in the following solvents-

  • Water (solubility is 27 g /100 ml at 200 C and 30.7 g/100 g at 250 C).
  • Glycerol.

Na2SO3 is basically soluble in the above two polar solvents due to having similar nature. Only polar molecules get dissolved in polar solvent because they will be able to break the hydrogen bonding present in water molecule due to positive end-negative end stabilizing interaction between solute and solvent molecule.

 Is Na2SO3 solid or gas?

Physical state or solid, liquid and gaseous state depends upon the boiling and melting point of that molecule. Let us comment on this.

Na2SO3 is a white crystalline solid compound as it is an ionic compound. Ionic compounds are attached through very strong electrostatic force of attraction which acts between two oppositely charged ions. In Na2SO3, this strong coloumbic force is working between Na+ and SO32-.

Is Na2SO3 polar or nonpolar?

Polarity or non-polarity can be defined by the presence or absence of separation of electric charge. Let us talk about this in detail.

Na2SO3 is definitely a polar molecule as it is an ionic compound and ionic compounds are always polar. The polarity arises due to the presence of two opposite charge, Na+ and SO32- which are held together by strong electrostatic force of attraction in Na2SO3.

Is Na2SO3 acidic or basic?

An acid or base is the absence or presence of excess electron density which can be donated or accepted from other atoms. Let us determine it.

Na2SO3 is basic in nature. This salt is formed by the reacting of strong base, sodium hydroxide and weak sulphurous acid. Therefore, the pH of the aqueous solution is always more than 7.

It undergoes hydrolysis on reaction with H2O. The reaction is – SO32- + H2O = HSO3 + OH. Due to production of OHion, Na2SO3 shows basicity in water.

Is Na2SO3 electrolyte?

Electrolytes are dissociated in oppositely charged ions in aqueous solution or any other solvent. Let us talk about this in brief.

Na2SO3 is a strong electrolyte as it is an ionic compound. It is dissociated into Na+ and SO32- in aqueous solution. After dissolution in water, it is dissociated into sodium, sulfate and hydroxide ions.

Is Na2SO3 ionic or covalent?

Ionic character or covalency is determined depending upon the type of interaction present in the molecule. Let us determine it.

Na2SO3 is definitely an ionic compound because two different charge is attached through a strong coloumbic attraction force. Two sodium atoms transfer their last valence electrons to SO3 completely and becomes Na+ and SO3 becomes SO32-. The complete transferring of electrons makes Na2SO3 an ionic compound.


Na2SO3 has different uses in various fields like photography, in bleaching of wool preservatives of foods and medication. It also works as an antioxidant in the manufacture of pulp for paper and wooden products.

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