1. Valence Electrons

2. Electrons Electrons are found in orbitals within energy levels The regions in an atom where electrons are found are called orbitals Electrons usually occupy the lowest energy levels available in an atom

3. Valence electrons An electron in the outermost energy level of an atom is called a valence electron Ex. – The single electron of a hydrogen atom is a valence electron because it is the only electron the atom has – In a neon atom, its valence electrons are the eight electrons that are in the outermost energy level

4. Valence electrons

5. Chemical Reactivity The chemical reactivity of an atom is mainly determined by valence electrons Atoms with a complete (full) valence shell are not reactive Atoms with one or two valence electrons are highly reactive Orbitals that are empty, half-full, or full are more stable

6. Periodic Table