Atomic Number

* Definition: The atomic number represents the number of protons in an atom's nucleus.

* Key Points:

* Unique identifier: Every element has a unique atomic number, which defines its identity.

* Neutral atoms: In a neutral atom, the number of protons is equal to the number of electrons.

Mass Number

* Definition: The mass number represents the total number of protons and neutrons in an atom's nucleus.

* Key Points:

* Approximation: The mass number is an approximation of the atomic mass, as it doesn't account for the very small mass of electrons.

* Isotopes: Atoms of the same element can have different mass numbers due to variations in their number of neutrons. These are called isotopes.

In Summary:

* Atomic number determines the element's identity.

* Mass number gives a general idea of the atom's mass.

Let me know if you have any other questions about atomic structure!