Atomic Number:

* Definition: The number of protons in the nucleus of an atom.

* Symbol: Z

* Key Properties:

* Unique to each element.

* Determines the element's identity.

* Atoms of the same element always have the same atomic number.

* Example: Carbon has an atomic number of 6, meaning all carbon atoms have 6 protons in their nuclei.

Mass Number:

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

* Symbol: A

* Key Properties:

* Can vary for different isotopes of the same element.

* Represents the approximate atomic mass of an atom.

* The mass number is usually a whole number, but it can vary slightly due to the binding energy of the nucleus.

* Example: Carbon-12 has a mass number of 12. This means it has 6 protons and 6 neutrons (12 total). Carbon-14 has a mass number of 14, meaning it has 6 protons and 8 neutrons (14 total).

In Summary:

* The atomic number defines the element, while the mass number describes a specific isotope of that element.

* The number of protons (atomic number) determines the chemical properties of an element.

* The number of neutrons (which affects the mass number) can influence the stability and radioactivity of an atom.