Hydrogen peroxide (H2O2) molecular geometry or shape, Lewis structure, electron geometry, hybridization, bond angle
Dihydrogen dioxide, commonly known as hydrogen peroxide, is represented by the chemical formula H2O2.
It exists as a clear colorless liquid at r.t.p. It is a potent oxidizing and bleaching agent, specifically useful in the paper, textile, and chemical manufacturing industries. Hydrogen peroxide is extremely toxic to the human skin and body.
In this article, we have discussed everything you need to know about the Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, hybridization, formal charges, and polarity of H2O2.
The Lewis dot structure of hydrogen peroxide (H2O2) consists of 2 oxygen (O) atoms at the center, single-covalently bonded to a hydrogen (H) atom, one at either side. 2 lone pairs of electrons are present on each of the two O-atoms, while there is no lone pair on either H-atom.
By following the simple steps given below, you can easily draw the Lewis structure of H2O2.
Steps for drawing the Lewis dot structure of H2O2
1. Count the total valence electrons present in H2O2
H2O2 consists of two distinct elements, i.e., hydrogen and oxygen.
Hydrogen (H) lies at the top of the Periodic Table with a single valence electron only. In contrast, oxygen (O) is present in Group VI A (or 16) of the Periodic Table, possessing 6 valence electrons.
Total number of valence electrons in hydrogen = 1
Total number of valence electrons in oxygen = 6
The H2O2 molecule comprises 2 O-atoms and 2 H-atoms.
∴ Therefore, the total valence electrons available for drawing the Lewis dot structure of H2O2 = 2(1) + 2(6) = 14 valence electrons.
2. Choose the central atom
By convention, the least electronegative atom out of all those available is chosen as the central atom while drawing the Lewis structure of a molecule.
The least electronegative atom can easily form covalent bonds with other atoms by sharing its electrons.
In H2O2, hydrogen (E.N = 2.20) is undoubtedly less electronegative than oxygen (E.N 3.44).
However, the H-atom is an exception as it cannot be chosen as the central atom in any Lewis structure. It can accommodate a total of 2 valence electrons, forming a single covalent bond with 1 adjacent atom only.
So we have no choice but to choose an O-atom as the central atom in the H2O2 Lewis dot structure.
Both the O-atoms are identical. Therefore, anyone O-atom can be considered a central atom in the structure shown below, while the H-atoms occupy terminal positions, one at the side of each oxygen atom.
3. Connect the outer atom with the central atom
In this step, each of the two O-atoms is joined to its adjacent H-atom via a single straight line. Also, the two O-atoms are joined to each other.
A straight line represents a single covalent bond, i.e., a bond pair containing 2 electrons.
In the above structure, there are 3 single bonds, i.e., 3(2) = 6 valence electrons are already consumed out of the 14 initially available.
Now let’s see where we can place the remaining valence electrons.
4. Complete the octet and/or duplet of the outer atoms
An O-atom needs a total of 8 valence electrons in order to achieve a stable octet electronic configuration.
In the Lewis structure obtained so far, if we suppose Oa as the central atom, then Obis marked a terminal atom.
An O-O and an O-H single bond represents a total of 4 valence electrons surrounding Ob. So, 4 more electrons are placed as 2 lone pairs around this oxygen atom to complete its octet.
In contrast, both terminal H-atoms already have a complete duplet, so we do not need to make any changes w.r.t the H-atoms.
5. Complete the octet of the central atom
Total valence electrons used till step 4 = 3 single bonds + electrons placed around Ob shown as dots = 3(2) + 4 = 10 valence electrons.
Total valence electrons – electrons used till step 4 = 14 – 10 = 4 valence electrons.
Hence, the remaining 4 electrons are placed as 2 lone pairs on the central O-atom, i.e., Oa, which automatically completes its octet.
Also, both the O-atoms are now equivalent.
As a final step, we just need to check the stability of the Lewis structure obtained above. We can do so using the formal charge concept.
6. Check the stability of Lewis’s structure using the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charges can be calculated using the formula given below.
Formal charge = [valence electrons- nonbonding electrons- ½ (bonding electrons)].
Now let us use this formula and the Lewis structure obtained in step 5 to determine the formal charges present on the H2O2-bonded atoms.
For each hydrogen atom
Valence electrons of hydrogen = 1
Bonding electrons = 1 single bond = 1(2) = 2 electrons
Non-bonding electrons = no lone pair = 0 electrons
What are the electron and molecular geometry of H2O2?
Hydrogen peroxide (H2O2) is an ‘’open-book-like’ bent, angular or V-shaped molecule w.r.t both the O-atoms. However, its ideal electron pair geometry is tetrahedral.
The presence of 2 lone pairs of electrons on each of the two central O-atoms leads to a strong repulsive effect, thus distorting the overall molecular geometry of H2O2.
Molecular geometry of H2O2
The molecular geometry or shape of H2O2 w.r.t each O-atom is bent, angular or V-shaped.
There are 2 lone pairs of electrons on both the O-atoms in H2O2, leading to strong lone pair-lone pair and lone pair-bond pair electronic repulsions. The terminal H-atoms tilt away from the two O-atoms at the center to minimize this strong repulsive effect.
Thus, the H2O2 molecule occupies a non-planar bent or V-shape, as shown below.
Electron geometry of H2O2
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electron geometry of a molecule containing a total of 4 electron density regions around the central atom is tetrahedral.
In H2O2, each of the two central O-atoms is surrounded by 2 bond pairs (O-O and O-H bonds) and 2 lone pairs of electrons, making a total of 4 electron density regions.
Hence, the ideal electron pair geometry of the H2O2 molecule is tetrahedral.
An easy trick to finding a molecule’s electron and molecular geometry is using the AXN method.
AXN is a simple formula representing the number of bonded atoms and lone pairs on the central atom.
It is used to predict the shape and geometry of a molecule using the VSEPR concept.
AXN notation for H2O2 molecule
A in the AXN formula represents the central atom. In the H2O2 molecule, an oxygen (O) atom is present at the center, so A = O.
X denotes the atoms bonded to the central atom. In H2O2, 1 H-atom and another O-atom are single-covalently bonded to the central O-atom. So X = 2 for H2O2.
N stands for the lone pairs present on the central atom. As per the Lewis structure of H2O2, the central O-atom carries 2 lone pairs of electrons. Thus, N = 2 for H2O2.
As a result, the AXN generic formula for H2O2 is AX2N2.
Now, you may have a look at the VSEPR chart below.
The VSEPR chart confirms that the molecular geometry or shape of a molecule with an AX2N2 generic formula is bent, angular or V-shaped, while its electron geometry is tetrahedral, as we already noted down for the hydrogen peroxide (H2O2) molecule.
Hybridization of H2O2
Both the O-atoms are sp3 hybridized in H2O2.
The electronic configuration of an oxygen (O) atom is 1s2 2s2 2p4.
During chemical bonding in H2O2, the 2s atomic orbital of oxygen hybridizes with its three 2p orbitals to produce four sp3 hybrid orbitals.
Each sp3 hybrid orbital has a 25 % s-character and a 75 % p-character. However, these sp3 hybrid orbitals are not equivalent.
The paired electrons present in two sp3 hybrid orbitals are placed as lone pairs on the oxygen atom.
Contrarily, the half-filled sp3 hybrid orbitals of oxygen form the O-O and O-H sigma bonds by sp3-sp3 and sp3-s orbital overlap, respectively. Refer to the figure drawn below.
A shortcut to finding the hybridization present in a molecule is using its steric number against the table shown below. The steric number of the O-atom in H2O2 is 4, so it has sp3 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of H2O2
Due to the non-planar, bent shape of H2O2 w.r.t, each O-atom, the H-O-O bond angle is reduced from an ideal value of 109.5° to 94.8° in the gaseous phase.
In the gas phase, the H2O2 molecules are widely spaced, having weak intermolecular forces of attraction.
Contrarily, in the closely-packed solid or crystalline phase, H2O2 molecules develop strong intermolecular hydrogen bonding, which restricts the motion of the molecules, and the H-O-O bond angle increases to 101.9°.
The O-O bond length is 145.8 pm, while the O-H bond length is 98.8 pm in hydrogen peroxide.
Hydrogen peroxide polarity: Is H2O2 polar or nonpolar?
As per Pauling’s electronegativity scale, a polar covalent bond is formed between two dissimilar atoms with an electronegativity difference between 0.4 and 1.6 units.
Two different types of covalent chemical bonds are present in H2O2, i.e., O-O and O-H.
The O-O bond is purely non-polar as it is formed between two identical oxygen atoms having no electronegativity difference.
In contrast, the O-H bond is strongly polar as an electronegativity difference of 1.24 units is present between an oxygen (E.N = 3.44) and a hydrogen (E.N = 2.20) atom.
Oxygen being strongly electronegative, attracts the O-H electron cloud largely towards itself. Thus, both O-atoms gain partial negative (δ–) charges while the adjacent H-atoms obtain partial positive (δ+) charges.
The strong dipole moment of each O-H bond point from Hδ+ to Oδ–.
It is due to the asymmetric bent shape of the H2O2 molecule that the O-H dipole moments stay uncancelled to yield an uneven charge distribution and, thus, an overall polar hydrogen peroxide molecule (net µ = 2.1 Debye).
The Lewis dot structure of hydrogen peroxide (H2O2) displays a total of 14 valence electrons, i.e., 7 electron pairs.
Two oxygen (O) atoms are present at the center of the molecule.
Each O-atom is bonded to an H-atom via a single covalent bond.
Both the O-atoms carry 2 lone pairs of electrons each.
Identify the number of bonding pairs and lone pairs of electrons in H2O2.
Out of the 7 electron pairs present in the Lewis dot structure of H2O2, there are 3 bond pairs and 4 lone pairs of electrons.
The bonding pairs comprise the O-O and 2 O-H bonds while 2 lone pairs are present on each O-atom.
What is the molecular geometry of H2O2 (HOOH)?
The molecular geometry or shape of H2O2 is bent, angular or V-shaped w.r.t each oxygen atom.
Why is the molecular shape of H2O2 different from its electronic geometry?
The molecular shape of H2O2 is bent or V-shaped, while its ideal electronic geometry w.r.t each O-atom is tetrahedral.
The presence of 2 lone pairs of electrons on each oxygen atom leads to strong lone pair-lone pair and lone pair-bond pair electronic repulsions, thus distorting the overall shape and geometry of H2O2.
H2O is water, and H2O2 is hydrogen peroxide. How are their shapes the same or different?
The shape of both H2O and H2O2 is the same w.r.t the central O-atoms, i.e., bent or angular.
In H2O, there is one O-atom at the center. It is single covalently bonded to 2 H-atoms, one on each side. 2 lone pairs of electrons present on the central O-atom lead to strong lone pair-lone pair and lone pair-bond pair electronic repulsions in H2O.
In H2O2, there are two O-atoms at the center, bonded to 1 H-atom on either side. 2 lone pairs of electrons on each of the two O-atoms lead to an even stronger electron-repulsive effect.
The molecule adopts a bent shape where the H-O-O bond angle is reduced to 94.8°.
How is the shape of H3O+ different from H2O2?
In the hydronium (H3O+) ion, 3 H-atoms are single covalently bonded to an O-atom at the center. It also has a formal charge of +1, which implies that the central O-atom carries a lone pair of electrons as well.
Lone pair-bond pair repulsions distort the geometrical symmetry of the molecular ion.
The total number of valence electrons available for drawing the H2O2 Lewis structure is 14.
The molecular geometry or shape of H2O2 w.r.t each O-atom is bent, angular, or V-shaped.
The ideal electron pair geometry of H2O2 is tetrahedral.
Both the O-atoms are sp3 hybridized in H2O2.
The H-O-O bond angle is 94.8° in the gaseous phase, while it is increased to 101.9° in the crystalline phase of H2O2, in which the hydrogen peroxide molecules get closely packed with restricted rotation.
H2O2 is a polar molecule (net µ > 0) due to the presence of two strongly polar O-H bonds and a non-planar, asymmetric bent shape.
Zero or no formal charges on the covalently bonded O and H-atoms in the H2O2 molecule ensure the extraordinary stability of the Lewis structure obtained in this article.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
2 thoughts on “H2O2 molecular geometry, lewis structure, bond angle, hybridization”
Keneau Arnet, III (aka “Kid Valence”)
Comprehensive to say the least… that is, close enough to “comprehensive” to suit the dilettante chemist.
Vishal Goyal
Thanks!
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Comprehensive to say the least… that is, close enough to “comprehensive” to suit the dilettante chemist.
Thanks!