Valence electrons are located in the outermost energy level or shell of an atom. These are the electrons involved in the atom's chemical bonding behavior and determining its reactivity. The number of valence electrons an atom has is determined by its position in the periodic table.
For main group elements (groups 1, 2, 13-18), the valence electrons are found in the highest-numbered (outermost) s and p orbitals.
For example:
- Group 1 elements (such as hydrogen, lithium, sodium) have 1 valence electron in the outermost s orbital.
- Group 2 elements (such as beryllium, magnesium, calcium) have 2 valence electrons in the outermost s orbital.
- Group 13 elements (such as boron, aluminum, gallium) have 3 valence electrons, with 2 in the outermost s orbital and 1 in the outermost p orbital.
For transition metals (groups 3-12), the valence electrons can be found in both the outermost s and d orbitals.
Understanding the location of valence electrons is important in predicting an atom's chemical behavior and how it will interact with other atoms to form compounds.