H2O2 is the chemical formula for hydrogen peroxide. Pure H2O2 is a non-flammable, strong oxidizing agent and a pale blue-colored liquid that is slightly more viscous than water. It is extremely poisonous upon inhalation. This polyatomic molecule has a molar mass of 34.01 g/mol.
So what is the polarity of this very commonly used surface cleaner, hydrogen peroxide (H2O2)? Is it a polar or a non-polar molecule?
Let’s find out in this article.
Is H2O2 polar or non-polar?
Hydrogen peroxide (H2O2) is a polar molecule. It consists of two oxygen (O) atoms and two hydrogens (H) atoms. The O-atoms are present at the center of the structure as O-O bond, while both H-atoms occupy side positions making O-H bonds, one on each side; overall, the molecule obtains a bent shape and molecular geometry.
An electronegativity difference of 1.24 units exists between an oxygen and a hydrogen atom in each of the O-H bonds in H2O2.
Thus, both O-H bonds are individually polar in the H2O2 molecule and possess a specific dipole moment value (symbol µ).
Furthermore, it is due to the asymmetric shape of the H2O2 molecule that the dipole moments of polar O-H bonds do not get canceled overall in the molecule. The electron cloud stays non-uniformly distributed over the molecule. Thus, H2O2 is a strongly polar molecule (net µ= 2.1 Debye).
A molecule is polar if there is a non-uniform charge distribution present in it. If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that the hydrogen peroxide (H2O2) molecule is overall polar.
Factors affecting the polarity of H2O2
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Hydrogen (H) belongs to Group I A of the Periodic Table. The electronic configuration of a hydrogen atom is 1s1. Hence, each H-atom in the H2O2 molecule has a deficiency of 1 more valence electron to obtain a full outer shell.
Conversely, Oxygen (O) is present in group VI A of the Periodic Table. The electronic configuration of an oxygen atom is 1s2 2s2 2p4. As per this electronic configuration, an O-atom has a total of 6 valence electrons. It is thus short of 2 valence electrons that are required so that an O-atom can achieve a complete octet electronic configuration.
Hence, in the H2O2 molecule, each of the two terminal H-atoms is covalently bonded with the central O-atom. The central O-atoms are also single-covalently bonded to each other.
2 valence electrons of oxygen consumed in covalent bonding out of the 6 initially available leaves behind 4 valence electrons i.e., 2 lone pairs on each oxygen atom, as shown in the Lewis dot structure drawn below.
In this way, all four atoms (two H-atoms and two O-atoms) attain complete duplet and octet electron configurations in their respective outer shells, via lone pairs and chemical bonding in H2O2.
The presence of two lone pairs of electrons on the central oxygen (O) atoms distorts the shape of the molecule and makes it occupy a bent shape.
Atom
Electronic configuration
Valence electrons
Hydrogen (1H)
1s1
1
Oxygen (8O)
1s2 2s2 2p4
6
The electronegativity of oxygen is 3.44, and that of hydrogen is 2.20. Thus, the electronegativity difference between the bonded oxygen and hydrogen atoms in each O-H bond is 1.24 units. So each O-H bond is strongly polar in the H2O2 molecule.
The more electronegative central O-atom strongly attracts the shared electron cloud away from the terminal H-atoms in each O-H bond present in the H2O2 molecule.
Zero electronegative difference exists between two identical O-atoms at the center of H2O2, so the O-O bond is non-polar.
However, it is due to strongly polar O-H bonds that the oxygen atoms present at the center of H2O2 gain partial negative (Oδ-) charges, while each terminal hydrogen atom obtains a partial positive (Hδ+) charge, as shown below.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.
So in the H2O2 molecule, the dipole moment of each O-H bond points from Hδ+ to Oδ- (as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, H2O2 is an AX2E2 -type molecule. To one O-atom at the center (A), two bonded pairs of electrons (X) are attached, and there are two lone pairs (E) on the central atom.
Due to the presence of two lone pairs of electrons on each central O-atom, the molecular geometry or shape of H2O2 is bent, angular, or V-shaped, which is different from its ideal electron pair geometry i.e., tetrahedral.
The H-O-O bond angle decreases to 94.8° in the gas phase and 101.9° in the solid/crystal phase from the ideal bond angle value (109.5°) in a tetrahedral molecule.
The lone pairs of electrons present on the central O-atoms in H2O2 lead to strong lone pair-lone pair and lone pair-bond pair repulsions in addition to the bond pair-bond pair electronic repulsions. This strong repulsive effect influences the molecule to adopt a distorted, asymmetrical shape.
It is due to this asymmetrical shape that the dipole moments of O-H polar bonds do not get canceled in the H2O2 molecule. The electron cloud stays non-uniformly distributed over the molecule. Thus, H2O2 is overall a polar molecule (net µ = 2.1 Debye).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), phosphorus trifluoride (PF3), Hydrogen peroxide (H2O2), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), ethane (C2H6), propane (C3H8), etc.
H2O2 has polar bonds due to an electronegativity difference of 1.24 units between the bonded oxygen (E. N= 3.44) and hydrogen (E. N= 2.20) atoms in each O-H bond.
Each O-H bond thus possesses a specific dipole moment.
However, it is due to the asymmetrical bent molecular shape of H2O2 that the individual O-H dipole moments do not get canceled, and the charged electron cloud stays non-uniformly spread over the molecule.
Consequently, hydrogen peroxideH2O2 is polar with a net dipole momentµ = 2.1 Debye.
Does H2O2 contain both polar and non-polar bonds?
Yes.
The electronegativity of oxygen is 3.44, while the electronegativity of hydrogen is 2.20. An electronegativity difference of 1.24 units exists between bonded O-atom and H-atom in each O-H bond.
Oxygen gains a partial negative (δ–) charge, while each hydrogen atom carries a partial positive (δ+) charge, resulting in the O-H bond being polar in H2O2.
In contrast, since central O-atoms have the same electronegativity, there is no difference in polarity across the O-O bond. Consequently, O-O bond is non-polar in the H2O2 molecule.
Why does the hydrogen peroxide (H2O2) molecule adopt a different molecular geometry from its ideal electron pair geometry?
The lone pairs of electrons present on the central O-atoms in H2O2 lead to strong lone pair-lone pairs and lone pair-bond pair repulsions in the molecule.
Consequently, distortion occurs in the shape and geometry of the H2O2 molecule. It thus adopts an open book-like, bent shape, and molecular geometry, different from its ideal electronic geometry i.e., tetrahedral.
Why is the dipole moment of hydrogen peroxide (H2O2) greater than water (H2O)?
H2O2 (net µ = 2.1 D) is more polar than H2O (net µ = 1.85 D), although both possess two polar O-H bonds and a bent molecular shape or geometry.
The difference in dipole moments and, thus, polarity exists as there are two O-atoms in H2O2, each containing 2 lone pairs of electrons.
A total of 4 lone pairs of electrons results in a stronger lone pair-lone pair and lone pair-bond pair repulsive effect; thus, greater distortion is witnessed in the shape and geometry of H2O2. The O-H dipole moments, both pointing in the same direction, undergo minimum cancellation in the maximally distorted shape. This leads to a higher net dipole moment.
Thus H2O2 is more strongly polar than H2O, in which there is only 1 O-atom containing 2 lone pairs of electrons.
Among HCN, CH4, and H2O2, which contains both polar and non-polar bonds?
A covalent bond is purely non-polar only if it is formed between two identical elemental atoms.
Among the three molecules mentioned above, only H2O2contains both polar and non-polar bonds. H2O2 possesses two polar O-H bonds and 1 non-polar O-O bond.
HCN is also a polar molecule overall. It consists of polar H-C and C-N bonds and possesses a linear shape.
CH4 is a non-polar tetrahedral molecule. It consists of weakly polar C-H bonds. The small dipole moments of the C-H bonds get canceled equally in the molecule, so it is overall non-polar.
Is there a formal charge on the bonded atoms in the H2O2 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
A zero formal charge is present on H-atoms and on central O-atoms; thus, the overall charge present on the hydrogen peroxide H2O2 molecule is (0) + (0) = 0.
Summary
Hydrogen peroxide (H2O2) is a polar molecule.
It consists of polar O-H bonds due to an electronegativity difference of 1.24 units between an oxygen and a hydrogen atom.
Hydrogen peroxide (H2O2) has an asymmetrical bent shape with an H-O-O bond angle of 94.8° in the gas phase, which increases to 101.9° in the solid/crystal phase.
The electron cloud stays non-uniformly distributed in the asymmetrical H2O2 bent shape.
Due to the presence of two lone pairs of electrons on the central O-atom, the dipole moment of polar O-H bonds does not get canceled.
The net dipole moment in H2O2 is net µ = 2.1 Debye, so it is overall polar.
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/
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