Non-metals form covalent bonds (molecular bonds) by sharing an electron-pair between them. For most atoms, the sharing of an electron-pair in a covalent bond allows them to obtain a stable electron configuration, following theoctet rule。

If the two bonding atoms have differentelectronegativitiesit results in the electron pair not being shared equally between the two atoms. If the difference in electronegativity is greater than 0.4 on the Pauling scale the bond is said to bepolar。If the difference is greater than 1.7 the bond is considered to be mainlyionic。然而,它不是一个尖锐的分歧ut a matter of the bond being主要是ionic when above 1.7.

Figure 1Polar covalent bond between chlorine and hydrogen. The distribution of electron density in the HCl molecule is uneven. Symbols δ+ and δ– indicate the polarity of the H–Cl bond.

The covalent bond between the atoms can be a σ (sigma) bond or a π (pi) bond, depending on thehybridizationof the bonding orbitals.