What primarily determines the valence of an atom?

The valence of an atom is primarily determined by the number of electrons present in its outer shell, also known as the valence shell. These outer shell electrons are crucial because they are involved in chemical bonding and reactions. Atoms tend to form bonds in order to achieve a stable electron arrangement, which is often analogous to the electron configuration of the nearest noble gas.

For example, if an atom has one or two electrons in its outer shell, it is likely to lose those electrons in order to achieve a full outer shell, thus exhibiting a positive valence. Conversely, if an atom has five, six, or seven electrons in its outer shell, it is more likely to gain or share electrons to fill its outer shell, resulting in a negative or neutral valence.

In summary, the behavior of atoms during chemical bonding is fundamentally influenced by the number of electrons they have in their outermost shell, establishing the importance of this characteristic in determining the valence of an atom.