Valence electrons are defined as?

Valence electrons are the electrons located in the outermost shell of an atom, which play a crucial role in chemical bonding and reactivity. These electrons are significant because they are involved in interactions with other atoms, allowing for the formation of bonds that drive chemical reactions. The number of valence electrons determines an atom's ability to bond with others; for example, elements in the same group of the periodic table often exhibit similar bonding behaviors due to having the same number of valence electrons.

In contrast, electrons in the innermost shell are not involved in bonding and are considered core electrons. Electrons that are tightly bound to the nucleus are typically those that are not involved in chemical reactions, as they reside in lower energy levels closer to the nucleus. Additionally, the definition of electrons that have been lost by an atom refers to ions, which have gained or lost electrons but does not specifically address the concept of valence electrons, which are inherently present in the outermost shell prior to any loss or gain.