Atoms that are both nonmetals and have similar, relatively high electronegativities tend to form covalent bonds by sharing electrons rather than transferring them.

Core idea

  • Covalent bonds form when atoms share pairs of valence electrons to achieve stable outer shells (octet or duplet).
  • This sharing is favored when neither atom can easily lose or gain electrons completely, which is typical of nonmetals.

What type of atoms?

  • Nonmetal–nonmetal pairs (for example H–H, O–O, C–H, N–H, Cl–Cl) are the classic covalent-bond formers.
  • Atoms with an electronegativity difference less than about 2.0 (on the Pauling scale) usually form covalent rather than ionic bonds.

Extra details students are often asked

  • If the two nonmetal atoms have very similar electronegativities , the bond is often nonpolar covalent (like H₂ or Cl₂).
  • If there is a moderate difference in electronegativity, the bond is polar covalent (like O–H in water).

In school-exam wording: “Covalent bonds typically form between nonmetal atoms with small electronegativity differences that share valence electrons to complete their octet.”