College Biology Exam 1 Practice Test 2026 – Your Complete All-in-One Guide for Exam Success!

Sharing one or more pairs of electrons between two atoms forms a covalent bond. This happens when the atoms have similar electronegativities, typically nonmetals, so neither atom fully transfers electrons to the other. Instead, they share electrons to fill their outer shells, creating a stable molecule. The number of shared electron pairs determines bond strength and order: one pair for a single bond, two for a double bond, three for a triple bond. Covalent bonds can be nonpolar if the sharing is even, or polar if there’s an uneven pull toward one atom due to differing electronegativities. Ionic bonds arise from electron transfer and electrostatic attraction between ions, hydrogen bonds are weak intermolecular attractions involving a hydrogen atom, and metallic bonds involve a lattice of metal cations with delocalized electrons. The shared-electron picture is the hallmark of covalent bonding.