What is the significance of the atomic number?

The atomic number of an element signifies the number of protons in the nucleus of its atom.

The atomic number, also known as the proton number, is a fundamental property of an atom that defines its chemical identity. It is denoted by the symbol 'Z' and is always a whole number. The atomic number is unique to each element and is used to organise elements in the Periodic Table.

The atomic number is crucial because it determines the number of protons in the nucleus of an atom. Since atoms are electrically neutral, the atomic number also indicates the number of electrons in an uncharged atom. These electrons occupy various energy levels around the nucleus and are involved in chemical reactions. Therefore, the atomic number indirectly influences the chemical behaviour of an element.

For example, hydrogen has an atomic number of 1, which means it has one proton in its nucleus and one electron in its energy level. Oxygen, with an atomic number of 8, has eight protons and eight electrons. These differences in atomic numbers result in different chemical properties. Hydrogen is a highly reactive gas, while oxygen supports combustion.

Furthermore, isotopes of the same element have the same atomic number but different mass numbers due to varying numbers of neutrons. This further emphasises the importance of the atomic number in defining an element, as isotopes of the same element share the same chemical properties.

In summary, the atomic number is a fundamental characteristic of an element. It determines the number of protons and electrons in an atom, thereby influencing its chemical properties and its position in the Periodic Table. It also helps distinguish between different elements and their isotopes.