What determines an atom's chemical properties?

The chemical properties of an atom are determined primarily by its electrons, particularly the arrangement of electrons in the outermost shell, known as the valence shell. Electrons are responsible for the interactions between atoms that lead to chemical bonding.

The number of electrons in an atom dictates how it will bond with other atoms, influencing the type of chemical reactions it can undergo. For example, elements with similar electron configurations, particularly those in the same group of the periodic table, exhibit similar chemical behaviors.

While protons (which determine an element's identity and its atomic number) and neutrons (which contribute to the atomic mass) are also important in defining the structure of an atom, they do not directly influence how an atom interacts chemically. Molecules, which are formed from two or more atoms bonded together, are the result of these interactions but do not determine the properties of singular atoms. Therefore, it is the electrons that fundamentally dictate the chemical properties and reactivity of an atom.