Valence electrons are the outermost electrons of an atom and play a crucial role in chemical bonding. They determine how an atom interacts with other atoms, influencing the formation of molecules and compounds. The number of valence electrons varies among different elements, which can be found in the periodic table. In general, elements in the same group of the periodic table have the same number of valence electrons, leading to similar chemical properties. For example, elements in the group of alkali metals each have one valence electron, making them highly reactive. Understanding valence electrons helps explain the behavior of elements in chemical reactions.