Valence electrons are the electrons located in the outermost energy level or shell of an atom. These electrons are important in determining the chemical properties of an element because they are involved in chemical bonding and interactions with other atoms.
Here are a few key reasons why only valence electrons significantly affect chemical properties:
Chemical Bonding: Valence electrons participate in the formation of chemical bonds. Atoms with incomplete outermost energy levels tend to gain, lose, or share electrons to achieve a more stable electron configuration, typically with eight valence electrons (the octet rule). By sharing or transferring valence electrons, atoms can form covalent bonds (sharing electrons) or ionic bonds (transferring electrons). The nature and strength of these bonds significantly influence the chemical properties of substances.
Reactivity: The number and arrangement of valence electrons determine an atom's reactivity. Atoms with a few valence electrons are often more reactive since they have a greater tendency to gain or share electrons to achieve a stable electron configuration. Elements with a full complement of valence electrons (inert gases or noble gases) tend to be unreactive or have low reactivity due to their stable configurations.
Formation of Chemical Compounds: Valence electrons determine how atoms combine to form chemical compounds. The interactions and sharing of valence electrons between atoms lead to the formation of molecules and compounds with unique properties. The types and arrangements of elements and their valence electrons within a compound dictate its chemical behavior, such as its stability, reactivity, and physical properties.
Outermost Energy Level Interactions: Valence electrons are located in the outermost energy level, farthest from the positively charged nucleus. This means they are more loosely held and more readily available for chemical interactions with other atoms. The interactions between the outermost energy levels of atoms determine the ways in which elements can combine and form compounds.
While the core electrons (inner electrons) also contribute to the overall electron configuration of an atom, they are generally shielded by the valence electrons and have less influence on chemical properties. It is the valence electrons that primarily dictate the chemical behavior, bonding capabilities, and reactivity of an element.