Valence Electron

Summary: An electron in the outermost shell of an atom. Determines the chemical properties and bonding behaviour. Tags: igcse chemistry definition atomic-structure bonding Created: 2026-07-14 Last Updated: 2026-07-14

Valence electrons are the electrons located in the outermost occupied electron shell (highest principal energy level) of an atom, and they are the electrons that participate directly in chemical bonding, determining both the type and number of bonds an atom can form. The number of valence electrons corresponds directly to the group number in the Periodic Table for main-group elements — for instance, all Group 1 elements have one valence electron (e.g., sodium with electron configuration 2,8,1), Group 2 elements have two valence electrons, Group 16 elements have six, and Group 17 halogens have seven valence electrons. Atoms form chemical bonds — whether ionic, covalent, or metallic — in order to achieve a stable valence electron configuration, typically a full outer shell of eight electrons (the octet rule) for most atoms, or two electrons (the duet rule) for hydrogen and helium which only require filling the first shell. During ionic bonding, metals lose their valence electrons to form positive cations while non-metals gain valence electrons to form negative anions; in covalent bonding, atoms share valence electrons to achieve a full outer shell; and in metallic bonding, valence electrons are delocalised into a sea of electrons. In IGCSE exams, you must be able to determine the number of valence electrons from an element’s position in the Periodic Table, use this information to predict the charge on the ion the element will form or the number of covalent bonds it will make, and draw dot-and-cross diagrams that accurately show valence electrons.

Key term — IGCSE Chemistry (0620/0971) glossary.