Is H2O (water) polar or nonpolar? - Polarity of Water
It is impossible to imagine life without water. H2O is the chemical formula for water. Water is a universal solvent. It adopts the color, the taste, and the smell of different chemical compounds that dissolve in it and there are many chemical compounds that can do so.
Just like water is important for all life forms on Earth so is the importance of studying its chemistry. Polarity is one such chemical property.
Therefore, in this article, we will explain whether H2O is polar or nonpolar, so, continue reading.
Is water (H2O) polar or nonpolar?
Water (H2O) is a highly polar molecule. It is composed of two hydrogens (H) atoms bonded to the central oxygen (O) atom. Due to the difference in electronegativity between an O and an H atom, each O-H bond in H2O is polar.
Water has an asymmetric V or bent shape which retains the polarity of O-H bonds. Thus, H2O is a polar molecule with a net dipole moment greater than 0.
Unequal charge distribution between different centers of a molecule results in the formation of polar molecules.
The shifting of electrons from one point to another in a covalent bond leads to bond polarity.
The asymmetric arrangement of these polar bonds ultimately contributes to the overall molecular polarity.
There are three factors that control the polarity of H2O namely:
Electronegativity
Dipole moment
Molecular geometry or shape
Below is a detailed discussion on each of these three factors which will help you in understanding the polar nature of H2O better.
Factors affecting the polarity of H2O
Electronegativity
An atom’s electronegativity refers to its affinity toward electrons. Just like a magnet attracts another, electronegativity is the ability of an atom to attract a shared pair of electrons from a covalent bond.
If a covalent bond is formed by the combination of two identical atoms such as H2 or O2 then it is purely non-polar in nature.
This is because there is no difference in electronegativity between the bonded atoms, so the electron cloud stays equally shared between both the bonded atoms.
However, if a covalent bond is made up of two dissimilar atoms such as an O-H bond with a difference in electronegativity of O and H atoms then it is a polar covalent bond.
Generally, polar covalent bonds have an electronegativity difference between the bonded atoms greater than 0.5 units.
Oxygen is highly electronegative (E.N= 3.44). It is more electronegative than hydrogen (E.N = 2.2).
Due to this electronegativity difference (3.44 -2.2 = 1.24 units), oxygen strongly attracts the shared electron cloud from each of the two O-H bonds in the H2O molecule.
Oxygen gains a partial negative charge (Oδ-) while each hydrogen obtains a partial positive charge (Hδ+ ). Thus, each O-H bond in the H2O molecule is polar. This is called the bond polarity of water.
Dipole moment
The dipole moment is a vector quantity that represents the polarity of a bond and/or a molecule.
It has a symbol µ and is defined as the product of electrical charge (Q) and charge separation i.e., bond length (r). Debye (D) is the symbol used for dipole moment.
⇒ µ= Q.r
It points from the partial positive center to the partial negative center of a bond or a molecule.
As we have already seen that each O-H bond in the H2O molecule is polar. That means the O-H bonds have a particular dipole moment value.
The dipole moment of an O-H bond points from the positive center (Hδ+) to the negative center (Oδ-) and has µ > 0, as shown in the figure below.
Oxygen uses its two valence electrons to bind with one hydrogen atom on each side. In this way, O achieves a stable octet configuration while each H achieves a duplet electronic configuration.
However, two lone pairs of electrons are also present on the central oxygen (O) atom.
According to the Valence Shell Electron Pair Repulsion (VSEPR) theory of chemical bonding, H2O is an AX2E2 type molecule.
Around the central oxygen atom (A), there are two bond pairs (X) and two lone pairs of electrons (E).
The ideal electronic geometry for an AX4 type molecule is tetrahedral. But, the presence of two lone pairs in H2O leads to lone pair-lone pair and lone pair-bond pair repulsions which decreases the bond angle from the ideal 109.5° to 104.5°.
The molecule (H2O) attains an asymmetric bent shape. Due to this asymmetric arrangement of atoms, the effect of individual O-H dipole moments adds up. Thus, H2O is a polar molecule overall with a net dipole moment of 1.85 D.
Difference between polar and non-polar molecules
Polar molecule
Non-polar molecule
Atoms having 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 0
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3) and sulfur dioxide (SO2), etc.,
Examples include oxygen (O2), nitrogen (N2), methane (CH4), and carbon dioxide (CO2).
H2O is made up of polar O-H bonds. Due to the difference in electronegativities of O and H atoms, O strongly attracts the shared electron cloud from each O-H bond.
O attains a partial negative charge while each H obtains a partial positive charge.
The individual dipole moments of O-H bonds are enhanced due to the asymmetric, bent shape of H2O.
Thus, H2O has a net dipole moment of 1.85 D, and it is a polar molecule.
Which of the following is non-polar? a) SO2 b) CO2 c) H2O d) NH3?
Out of all the four molecules, CO2 is a non-polar molecule while all the others are polar.
This is because of the symmetric linear shape of CO2 that cancels C=O dipole moments in opposite directions.
On the other hand, each of SO2, H2O, and NH3 have asymmetric shapes with unequal charge distribution.
SO2 and H2O have angular or bent shapes while NH3 has a trigonal pyramidal shape. Thus, these molecules are polar with a net dipole moment > 0.
Both H2S and H2O are polar molecules. But H2O is certainly more polar than H2S. The two molecules are quite similar in shape and bonding.
In both cases, two hydrogen atoms are bonded to an atom from group VII A (or 16) of the Periodic Table.
But oxygen is more electronegative than sulfur.
Due to a small electronegativity difference between H and S atoms in H2S, each H-S bond is very less polar. The molecule is polar because of the asymmetric arrangement of these atoms.
On the other hand, H2O is polar, and it contains polar bonds as well.
Why H2O bond angle is greater than the bond angle in an H2S molecule?
The H-O-H bond angle is 104.5 ° while the H-S-H bond angle is 92.1 °. This is because an S atom is larger in size than an O atom. The electronegativity of S is less than that of O.
Bond pair-bond pair repulsions between S-H bonds are weaker thus a greater effect of lone pair-bond pair repulsions, so the bond angle decreases further in the bent shape of H2S.
How do polar water molecules get attracted to each other?
Water molecules get attracted to each other using their oppositely charged Oδ- and Hδ+ ends.
The partially positive hydrogen of one H2O molecule develops a hydrogen bond with the partially negative oxygen of a second H2O molecule and vice versa.
Water is a universal solvent, that is also because of its hydrogen bonding ability.
The chemical compounds that dissolve in water are called hydrophilic i.e., water-loving.
Explain hybridization in H2O?
If we talk about the hybridization present in a water molecule then the central oxygen atom is sp3 hybridized. The electronic configuration of Oxygen is 1s22s22p4.
During chemical bond formation, the 2s orbital hybridizes with all the three 2p orbitals to produce 4 sp3 hybrid orbitals of equivalent energy.
Two sp3 hybrid orbitals contain paired electrons which are situated as two lone pairs on oxygen.
While the other two sp3 orbitals, each contain a single unpaired electron only.
These two hybrid orbitals are consumed in sigma bond formation with 1s orbitals of the H atoms.
Summary
Water (H2O) an essentially important molecule is polar in nature.
It has two O-H bonds. Each O-H bond is polar due to the electronegativity difference between O and H atoms.
The asymmetric bent shape of H2O further endorses the polarity of water.
Two lone pairs present on oxygen cause a repulsive effect so that water attains a bent shape with a 104.5° H-O-H bond angle and 95.7 pm O-H bond length.
The dipole moments of O-H bonds do not get canceled rather their effect is enhanced due to the molecule’ asymmetric shape.
So, H2O is a polar molecule with a net dipole moment of 1.85 D
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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