What determines the properties of a chemical element?

The properties of a chemical element are fundamentally determined by the behavior of its valence electrons. Valence electrons are the outermost electrons in an atom and play a crucial role in chemical reactions and bonding with other atoms. They influence how an element interacts with others, which directly affects its reactivity, electrical conductivity, and the types of compounds it can form.

The arrangement and behavior of valence electrons dictate whether an atom will gain, lose, or share electrons when forming bonds. This is why for many properties, such as the ability to conduct electricity or the type of chemical bonds formed (ionic, covalent, etc.), the valence electrons are the primary factor.

While the number of protons defines the identity of the element and the number of neutrons can impact the stability of the nucleus (contributing to isotopes), it is the valence electrons that primarily determine the element's chemical characteristics and its behavior in reactions. The total weight of the atom (which involves both protons and neutrons) does not give insight into how the atom will interact chemically. Thus, focusing on the behavior of valence electrons is key to understanding the properties of a chemical element.