How is the atomic number defined?

The atomic number is defined as the number of protons in the nucleus of an atom. This fundamental property determines the identity of an element; for instance, all carbon atoms possess six protons, giving carbon an atomic number of six. The atomic number is crucial because it not only defines the element but also determines its position in the periodic table and its chemical properties.

The atomic number also informs us about the number of electrons in a neutral atom, since the number of protons equals the number of electrons, establishing the atom’s charge balance. Hence, while the number of electrons plays a role in the behavior of the atom, it is the protons in the nucleus that are the defining characteristic of the element itself.

Understanding the atomic number is foundational for studying the structure of atoms and the behavior of elements in chemical reactions.