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Electrons in a Chemical Bond

When atoms join, they share electrons that form a cloud around the nuclei. In covalent bonds the electron density is shared equally, but in polar bonds the electrons are pulled toward the more electronegative atom, creating a slight charge imbalance.

Determining Polarity

Polarity hinges on electronegativity, the pull each atom exerts on shared electrons. Calculate the electronegativity difference:

• 0.4–1.7 → polar covalent bond
• >1.7 → ionic character (electrons transfer to the more electronegative atom)
• <0.4 → nonpolar covalent bond (equal sharing)

Dipole Moment

Polar bonds generate a dipole moment: a negative partial charge on the more electronegative atom and a positive partial charge on the other. The vector sum of all bond dipoles gives the molecule’s net dipole moment, influencing properties such as water’s high surface tension.

Polar vs. Nonpolar Molecules

A molecule can contain polar bonds yet be overall nonpolar if the dipoles cancel out. For instance, CO₂ has two polar C–O bonds (difference 1.0), but the linear geometry makes the two dipoles equal and opposite, yielding a nonpolar molecule.