Nonpolar and Polar Covalent Bonds

Electronegativity differences between bonded atoms dictate the type of covalent bond formed:
- A small electronegativity difference leads to a nonpolar covalent bond.
- A large electronegativity difference leads to a polar covalent bond.

Key Characteristics:
- Formed between atoms with similar electronegativities.
- Shared electrons are not pulled significantly more strongly by either atom.
- Electrons are shared evenly across the bond.
Example — Methane ( $CH_4$ ):
- Composed of carbon ( $C$ ) and hydrogen ( $H$ ) atoms.
- Carbon and hydrogen have similar electronegativity values.
- Because neither atom exerts a much stronger pull on the shared electrons, nonpolar covalent bonds hold the methane molecule together.

Key Characteristics:
- Formed between atoms with very different electronegativities.
- One atom exerts a much stronger attractive force on the shared electrons than the other atom.
Dynamics of Partial Charges:
- Electrons spend more time near the atom with higher electronegativity, giving that atom a slightly negative charge ( $\delta^-$ ).
- Electrons spend less time near the atom with lower electronegativity, giving that atom a slightly positive charge ( $\delta^+$ ).
Example — Water Molecule ( $H_2O$ ):
- Composed of oxygen ( $O$ ) and hydrogen ( $H$ ) atoms.
- Oxygen and hydrogen possess very different electronegativity values.
- Oxygen attracts shared electrons much more strongly than hydrogen does.
- Since electrons spend more time near the oxygen atom, oxygen acquires a slightly negative charge ( $\delta^-$ ).
- Since electrons spend less time near the hydrogen atoms, the hydrogen atoms acquire a slightly positive charge ( $\delta^+$ ).