Why are water molecules polar?
For two reasons. To be polar, there must be a charge separation between the positive end and the negative end.
First, there is an electronegative difference between H and O; that is, H and O don't have the same attraction for the electrons that make up the bond between the H atoms and the O atom. (O has an EN of 3.5 and H is 2.1; thus, the O atom pulls the electrons closer than H atoms which makes the H atoms lightly positive and the O atom slightly negative.)
Second, the H-O-H angle is NOT 180 degrees; that is, it is not a linear molecule. If it were a straight line molecule the H-O dipole on the left side would exactly cancel the 0-H bond on the right side and the net dipole moment would be zero. When we measure the dipole moment of water, we find it has a permanent dipole moment; therefore, we know it isn't linear. It is a bent molecule in geometry; something like this.
O-H
|
H
I hope this helps.
Water molecules are polar because of the unique arrangement of atoms within the molecule. A water molecule consists of one oxygen atom and two hydrogen atoms. The oxygen atom is more electronegative (attracted to electrons) compared to hydrogen, which means it has a greater ability to pull shared electrons towards itself.
In a water molecule, the oxygen atom pulls the shared electrons closer to itself, creating a partial negative charge (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms. This separation of charges within the molecule is known as a dipole.
To understand why water molecules are polar, you can examine the electronegativity difference between oxygen and hydrogen using a periodic table. Oxygen has an electronegativity of 3.44, whereas hydrogen has an electronegativity of 2.20. The difference in electronegativity values (3.44 - 2.20 = 1.24) is significant, indicating that there is a considerable electron density shift towards the oxygen atom in a water molecule.
This polarity of water molecules gives rise to hydrogen bonding, which is a strong type of intermolecular attraction. The δ+ hydrogen atom of one water molecule attracts the δ- oxygen atom of another water molecule, forming a hydrogen bond. These hydrogen bonds contribute to various unique properties of water, including its high boiling point, surface tension, and ability to dissolve other polar molecules.
Overall, water molecules are polar due to the unequal sharing of electrons between the oxygen and hydrogen atoms, resulting in a dipole moment within the molecule.