The bent molecular structure of water, combined with the difference in electronegativity between oxygen and hydrogen, causes an uneven distribution of electron density, making the molecule polar.
Here's a breakdown of how the structure impacts polarity:
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Bent Shape: Water (H₂O) has a bent, or V-shaped, geometry due to the two bonding pairs and two lone pairs of electrons around the central oxygen atom. This shape prevents the bond dipoles (the polarities of the individual O-H bonds) from canceling each other out. If water were linear, the bond dipoles would be equal and opposite, resulting in a nonpolar molecule.
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Electronegativity Difference: Oxygen is significantly more electronegative than hydrogen. This means oxygen has a stronger pull on the shared electrons in the covalent O-H bonds. Consequently, the electrons spend more time closer to the oxygen atom, giving it a partial negative charge (δ-) and the hydrogen atoms partial positive charges (δ+).
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Net Dipole Moment: Because of the bent shape and the electronegativity difference, the individual bond dipoles add up to create a net dipole moment for the entire water molecule. This net dipole moment makes water a polar molecule, meaning it has a positive end (near the hydrogens) and a negative end (near the oxygen).
In summary, the water molecule's polarity arises from its bent shape, which prevents the cancellation of bond dipoles created by the significant electronegativity difference between oxygen and hydrogen. The uneven sharing of electrons creates areas of partial positive and negative charge, resulting in a polar molecule.
