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How does the electronegativity difference between atoms affect bond polarity?

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Diagram showing the formation of a polar covalent bond in a water molecule, with two hydrogen atoms bonding to one oxygen atom to form H2O, illustrating shared electrons and chemical reaction. — covalent bond In polar covalent bonds, such as that between hydrogen and oxygen atoms, the electrons are not transferred from one atom to the other as they are in an ionic bond. Instead, some outer electrons merely spend more time in the vicinity of the other atom. The effect of this orbital distortion is to induce regional net charges that hold the atoms together, such as in water molecules.

Bond polarity is determined by the relative electronegativity of the bonded atoms, which is the power of an atom to attract shared electrons toward itself.12

When atoms of different elements form a covalent bond, the more electronegative atom draws the shared electron pair closer, acquiring a partial negative charge, while the other atom acquires a partial positive charge. This distribution of charge creates an electric dipole, resulting in a polar bond.12

As the electronegativity difference between the two atoms increases, the partial charges become larger, increasing the dipolar character of the bond. Bonding is best understood as a continuum:12
* Nonpolar bonds: Occur when atoms have identical electronegativities (e.g., $H_{2}$ ), resulting in equal electron sharing and a dipole moment of zero.12
* Polar bonds: Occur when there is an electronegativity difference, creating partial charges.12
* Ionic bonds: Occur when the electronegativity difference is very large, causing the more electronegative atom to effectively gain complete control over the electron pair.12