NCEA Level 2 Chemistry Practice Exam

The smallest number associated with an element on the periodic table, known as the atomic number, indicates the number of protons found in the nucleus of an atom of that element. This number is fundamental because it defines the identity of the element; for instance, carbon has an atomic number of 6, meaning it has 6 protons.

The atomic number also determines the position of the element on the periodic table and helps to identify its chemical properties, as elements with the same number of protons often share similar characteristics due to their electronic structure. In contrast, the element symbol represents the shorthand notation for an element (like H for hydrogen), atomic weight refers to the average mass of an atom considering isotopes, and the mass number is the total count of protons and neutrons in an atom's nucleus. Thus, the atomic number is a key concept in understanding the structure and categorization of elements.