What bond does a nonmetal and a nonmetal make?
A nonmetal and a nonmetal make a covalent bond in which valence electrons are shared between the atoms. The shared electron density stabilizes both atoms by helping each approach a noble-gas-like valence configuration, producing discrete molecules or network covalent solids depending on the elements involved.
Covalent bonding features shared electron density between two nonmetals. Bond polarity ranges from nonpolar covalent (nearly equal sharing) to polar covalent (unequal sharing) when electronegativities differ.
Electron sharing and covalent bonding
Nonmetals have relatively high ionization energies and tend to attract electrons strongly. Complete electron transfer between two nonmetals is energetically unfavorable in most cases, so the bonding interaction concentrates on sharing. A covalent bond represents a region of high electron probability located between the nuclei, lowering potential energy by simultaneously attracting both nuclei.
Bond order and shared pairs
A single covalent bond corresponds to one shared electron pair, a double bond corresponds to two shared pairs, and a triple bond corresponds to three shared pairs. Greater bond order generally correlates with shorter bond length and higher bond energy, while polarity is governed mainly by electronegativity differences rather than bond order alone.
Electronegativity difference and bond polarity
Unequal sharing arises when one atom is more electronegative and draws the shared electron density closer, producing partial charges \(\delta^-\) and \(\delta^+\) and a bond dipole. The electronegativity difference is expressed as \(\Delta \chi = |\chi_A - \chi_B|\).
| Electronegativity difference | Bond description | Electron sharing pattern | Typical outcome |
|---|---|---|---|
| \(\Delta \chi \approx 0\) to \(0.4\) | Nonpolar covalent | Nearly equal electron density between atoms | Little to no bond dipole |
| \(0.4\) to \(1.7\) | Polar covalent | Unequal electron density; partial charges form | Bond dipole; polarity affects intermolecular forces |
| \(\gtrsim 1.7\) | Strongly ionic character (rule of thumb) | Electron density largely localized on one atom | Ionic lattice often favored (typically metal–nonmetal) |
These cutoffs are conventions used in general chemistry. Many real bonds lie on a continuum between ideal covalent and ideal ionic bonding.
Illustrative polarity calculation
Hydrogen chloride is a polar covalent bond between two nonmetals (H and Cl). Using Pauling electronegativities \(\chi_{\mathrm{H}} = 2.20\) and \(\chi_{\mathrm{Cl}} = 3.16\):
\[ \Delta \chi = |3.16 - 2.20| = 0.96 \]The value \(\Delta \chi = 0.96\) lies in the polar covalent range, so the shared electron density is pulled toward chlorine, producing \(\delta^- \) on Cl and \(\delta^+ \) on H.
Visualization of shared electrons in a covalent bond
Examples that fit “nonmetal and nonmetal” bonding
- Nonpolar covalent molecules: \(\mathrm{Cl_2}\), \(\mathrm{N_2}\), \(\mathrm{O_2}\) (same atoms, \(\Delta \chi = 0\)).
- Polar covalent bonds within molecules: \(\mathrm{HCl}\), \(\mathrm{H_2O}\), \(\mathrm{NH_3}\) (different atoms, moderate \(\Delta \chi\)).
- Network covalent solids: diamond (C), quartz \(\mathrm{SiO_2}\) (extended covalent bonding rather than discrete molecules).
Common confusions and edge cases
- Bond polarity vs molecular polarity: polar covalent bonds can cancel in symmetric geometries, producing a nonpolar molecule (example: linear \(\mathrm{CO_2}\)).
- “Ionic” language in borderline cases: some nonmetal–nonmetal bonds show significant ionic character without forming ionic lattices; the continuum picture remains accurate.
- Coordinate covalent bonding: shared pairs donated by one atom can occur (Lewis acid–base adducts), while the bond remains covalent in electron-sharing character.
Conclusion
What bond does a nonmetal and a nonmetal make: covalent bonding dominates, with electron sharing as the defining feature. Electronegativity difference controls whether the bond is nonpolar covalent or polar covalent, and molecular geometry controls whether individual bond dipoles add or cancel.