The atomic number of an element is the number of protons in the nucleus of an atom of that element. It is a fundamental property of an element and is represented by the symbol Z.

Key points about atomic number:

* Unique to each element: Every element has a unique atomic number.

* Determines the element's identity: The number of protons defines what element an atom is. For example, all carbon atoms have 6 protons, and all oxygen atoms have 8 protons.

* Equal to the number of electrons in a neutral atom: In a neutral atom, the number of protons (positive charge) is equal to the number of electrons (negative charge).

* Located on the periodic table: The atomic number is usually shown above the element's symbol on the periodic table.

Example:

* Hydrogen (H) has an atomic number of 1, meaning it has 1 proton in its nucleus.

* Helium (He) has an atomic number of 2, meaning it has 2 protons in its nucleus.

Significance of atomic number:

* Understanding chemical properties: The atomic number plays a crucial role in determining an element's chemical properties and reactivity.

* Classifying elements: The atomic number is the basis for the arrangement of elements on the periodic table.

* Nuclear reactions: The atomic number changes in nuclear reactions, such as radioactive decay or nuclear fission.