Valenssielektronien

Valence electrons are the outermost electrons of an atom and play a central role in chemical bonding and reactivity. In the context of the periodic table, valence electrons for main-group elements are the electrons in the outermost s and p orbitals, and their count roughly corresponds to the element’s group number. For transition metals, valence electrons include both the outer s electrons and some of the d electrons, which can participate in bonding and influence chemistry in more complex ways.

Valence electrons participate in bonding by forming covalent bonds through sharing, or by transferring to form ionic bonds. They can also become delocalized in metallic bonding. The arrangement of valence electrons explains the octet rule for many main-group elements (aiming for eight electrons around an atom) and the duet rule for hydrogen and helium. Valence electrons underpin Lewis structures, bond order, and molecular geometry via VSEPR theory.

Periodic trends: across a period, elements gain valence electrons and reactivity changes; within a group, atoms have the same valence-electron count. Noble gases have full valence shells and are comparatively inert. In metals, valence electrons can move freely, giving rise to metallic bonding and electrical conductivity. In solids with delocalized electrons, the concept extends to the valence band in solid-state chemistry.

Limitations: the valence-electron model is a simplifying approximation. In molecules with resonance or in heavy elements, electron distribution involves d- or f-orbitals, and bonding cannot always be described by a single valence-electron count. Nonetheless, valence electrons remain a practical and central guide to understanding chemical bonding and reactivity.