The reactivity of an atom with another element depends on the arrangement of what subatomic particles?

The reactivity of an atom with another element is primarily determined by the arrangement of its electrons, particularly those in the outermost shell, or valence electrons. The behavior of these electrons influences how an atom interacts with others, whether it will form bonds, gain or lose electrons, or remain stable. Atoms strive for a full outer shell, leading to reactions that involve sharing or transferring electrons to achieve stability.

While protons play a crucial role in defining the identity of the element and its positive charge, and neutrons contribute to the atomic mass and stability of the nucleus, they do not directly affect chemical reactivity. The nucleus of an atom also does not participate in the chemical reactions that define reactivity, as it primarily holds protons and neutrons together through nuclear forces.

Therefore, understanding electron arrangements helps explain the diverse range of chemical behaviors exhibited by different elements, making electron configuration the fundamental aspect influencing an atom's reactivity.