How do you define atomic number?

The atomic number is the number of protons in the nucleus of an atom.

In more detail, the atomic number is a fundamental property of an element and is denoted by the symbol 'Z'. It determines the identity of an element and its position in the Periodic Table. For example, hydrogen has an atomic number of 1, meaning it has one proton in its nucleus, while carbon has an atomic number of 6, indicating it has six protons.

The atomic number is crucial because it defines the chemical behaviour of an element. Elements with the same atomic number have the same number of protons and, typically, the same number of electrons when they are neutral. These electrons are arranged in specific energy levels or shells around the nucleus, and their arrangement determines how the element reacts with others.

For instance, all atoms of oxygen have an atomic number of 8, meaning they all have eight protons. This consistency allows scientists to predict how oxygen will interact in chemical reactions, such as forming water when combined with hydrogen.

Additionally, the atomic number is used to distinguish between different isotopes of an element. Isotopes have the same number of protons but different numbers of neutrons. For example, carbon-12 and carbon-14 are both isotopes of carbon, with atomic numbers of 6, but they have different numbers of neutrons.

Understanding the atomic number helps in analysing the properties of elements and their compounds, making it a fundamental concept in chemistry and physics.