How to calculate formal charges of HSO4- with lewis structure?

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In covalently bonded molecules, formal charge is the charge assigned to an atom based on the assumption that the bonded electrons are equally shared between concerning atoms, regardless of their electronegativity.

The overall formal charge present on a molecule is a measure of its stability.

The fewer the formal charges present on the bonded atoms in a molecule (close to zero), the greater the stability of its Lewis structure.

In this article, we will calculate the formal charges present on the bonded atoms in [HSO4] and also the overall charge present on the molecular ion.

So, continue reading!

Name of the molecular ion Hydrogen sulfate
Chemical formula[HSO4]
The formal charge on the central S-atom0
The formal charge on single-bonded O-atom-1
The formal charge on double-bonded O-atoms0
The formal charge on the oxygen atom in the OH group0
The formal charge on the H-atom 0
The overall formal charge on HSO4 -1

How to calculate the formal charges on HSO4 atoms?

The formal charges can be calculated using the formula given below:

formal charge formula

The formal charge of an atom = [valence electrons of an atom – non-bonding electrons – ½ (bonding electrons)]

  • The valence electrons (V.E) of an atom are the total number of electrons present in its valence shell. Valence electrons can be calculated by locating the position of the elemental atom in the Periodic Table.
  • Non-bonding electrons (N.E) are the number of lone pairs present on the atom. (1 lone pair means 2 nonbonding electrons).
  • Bonding electrons (B.E) are the total electrons shared with the atom via covalent chemical bonds. (1 single bond means 2 bonding electrons).

Now let us use this formula to calculate the formal charges in the most preferred Lewis structure of the hydrogen sulfate ion, i.e., [HSO4].

The most preferred Lewis representation of [HSO4] is as shown below.

most stable hso4- lewis structure

It consists of a total of 32 valence electrons. A Sulfur S-atom is present at the center which is bonded to four atoms containing two atoms of oxygen (O) atoms via double covalent bonds while one oxygen atom and another oxygen atom of the O-H group is attached to the central sulfur atom, each via a single covalent bond.

No lone pair of electrons is present at the central S-atom. Each of the two double-bonded O-atoms contains 2 lone pairs while the single-bonded O-atom contains 3 lone pairs of electrons. The oxygen atom in the hydroxyl (OH) functional group in [HSO4]contains two lone pairs of electrons.

It is the best possible Lewis structure of the hydrogen sulfate ion [HSO4] because the formal charges are minimized in it, and thus, it is the most stable.

Let’s find out how we can determine the formal charges present on each atom in [HSO4] Lewis structure.

For the central sulfur atom

calculating formal charge on Sulfur atom in HSO4-

  • Valence electrons of Sulfur = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 2 single bonds + 2 double bonds = 2(2) + 2(4) = 12 electrons
  • Non-bonding electrons = no lone pair = 0 electrons
  • Formal charge on the Sulfur atom = 6 – 0 – 12/2 = 6 – 0 – 6 = 6 – 6 = 0

The formal charge on the Sulfur (S) atom in [HSO4] is 0.

For single-bonded oxygen atom

calculating formal charge on single bonded Oxygen atom in HSO4-

  • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 1 single bond = 2 electrons
  • Non-bonding electrons = 3 lone pairs = 3(2) = 6 electrons
  • Formal charge = 6 – 6 – 2/2 = 6 – 6 – 1 = 6 – 7 = -1

The formal charge on the single-bonded oxygen (O) atom in [HSO4] is -1.

For each double-bonded oxygen atom

calculating formal charge on double bonded Oxygen atom in HSO4-

  • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 1 double bond = 4 electrons
  • Non-bonding electrons = 2 lone pairs = 2(2) = 4 electrons
  • Formal charge = 6 – 4 – 4/2 = 6 – 4 – 2 = 6 – 6 = 0

The formal charge on the double-bonded oxygen (O) atom in [HSO4] is 0.

For the oxygen atom of the O-H group

calculating formal charge on O-H group atom in HSO4-

  • Valence electrons of oxygen = It is present in Group VI A = 6 valence electrons
  • Bonding electrons = 2 single bonds = 2(2) = 4 electrons
  • Non-bonding electrons = 2 lone pairs = 2(2) = 4 electrons
  • Formal charge = 6 – 4 – 4/2 = 6 – 4 – 2 = 6 – 6 = 0

The formal charge on the oxygen (O) atom of the hydroxyl [OH] functional group in [HSO4] is 0.

For hydrogen atom

calculating formal charge on Hydrogen atom in HSO4-

  • Valence electrons of hydrogen = It is present in Group I A = 1 valence electrons
  • Bonding electrons = 1 single bond = 2 electrons
  • Non-bonding electrons = 0 lone pairs = 0 electrons
  • Formal charge = 1 – 0 – 2/2 = 1 – 0 – 1 = 1– 1 = 0

The formal charge on the hydrogen atom in [HSO4] is 0.

This calculation shows that zero formal charges are present on the central S atom, double-bonded O-atoms, and the OH-bonded hydrogen and oxygen atoms in HSO4 Lewis structure.

However, the single-bonded O-atom carries a -1 formal charge which also accounts for an overall -1 formal charge on the hydrogen sulfate ion, as shown below. 

HSO4- lewis structure with formal charge

As a final step, the HSO4 Lewis structure is enclosed in square brackets, and a -1 formal charge is placed at the top right corner.

HSO4- formal charge

Also, check –

FAQ

How can you calculate [HSO4]  formal charges?

The formal charges present on the bonded atoms in HSO4 can be calculated using the formula given below:

V.E – N.E – B.E/2

Where –

⇒ V.E = valence electrons of an atom

⇒ N.E = non-bonding electrons, i.e., lone pairs

⇒ B.E = bonding electrons

What is the formal charge on S-atom in [HSO4]?

The central sulfur (S) atom carries a zero formal charge in [HSO4].

What is the formal charge on each double-bonded O-atom in [HSO4]?

Zero or no formal charges are present on each of the two double (S=O) bonded oxygen atoms in [HSO4].

What is the formal charge on the single-bonded O-atom in [HSO4]?

-1 formal charge is present on the single (S-O) bonded oxygen atom in [HSO4].

Do all four O-atoms carry the same formal charge in [HSO4]?

No, the single bonded O-atom carries a -1 formal charge, while no formal charges are present on the double bonded O-atoms, as well as on the oxygen (O) atom making the O-H group in [HSO4].

What is the formal charge on the H-atom in [HSO4]?

The formal charge on the H-atom in [HSO4] is 0.

What is the overall formal charge on [HSO4]?

The overall formal charge on [HSO4] is -1. 

Summary

  • The best possible Lewis structure of a molecule or molecular ion is the one in which the bonded atoms carry formal charges as close to zero as possible.
  • The formal charge formula is [ V.E – N.E – B.E/2].
  • In [HSO4], a zero formal charge is present on the central S-atom.
  • The double-bonded O-atoms have zero formal charges in [HSO4].
  • The oxygen (O) atom of O-H in [HSO4] also carries a zero formal charge.
  • Similarly, the hydrogen (H) atom of the O-H group in [HSO4]carries a zero formal charge.
  • The single-bonded O-atom carries a -1 formal charge in [HSO4].
  • The overall formal charge on [HSO4] Lewis structure is -1. Thus, it is a polyatomic monovalent anion.
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