Covalent bonds form primarily between nonmetal elements or between atoms of the same element, where electrons are shared rather than transferred. The tendency to form covalent bonds increases for elements toward the right side of the periodic table and for those that do not readily lose electrons to form ions. Core points

• Nonmetals commonly form covalent bonds with other nonmetals. This includes hydrogen, carbon, nitrogen, oxygen, sulfur, phosphorus, and the halogens (fluorine, chlorine, bromine, iodine, astatine). Some noble gases can form covalent bonds under certain conditions, but they are largely inert in standard conditions.

• Covalent bonds can be single, double, or triple, depending on how many electron pairs are shared between two atoms. Single bonds share one pair, double bonds share two pairs, and triple bonds share three pairs. This is especially common in organic molecules like H2O, CO2, and O2, and in many carbon-based compounds.

• The driving idea is that atoms achieve greater stability by completing their valence electron shells through sharing electrons with another atom, rather than transferring electrons to form ionic bonds. This shared-electron concept is the hallmark of covalent bonding.

• In many covalent compounds, bonds are directional and can be categorized as sigma (σ) bonds and pi (π) bonds, with σ bonds typically forming the first bond between two atoms and π bonds forming additional bonds in multiple-bond structures. This bond-type detail helps explain bond strength and molecular geometry.

If you’d like, I can tailor this to a specific context (e.g., introductory chemistry course, molecular biology examples, or chemistry of organics) and provide brief examples or a simple chart for quick reference.