1. Atomic Number:

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

* Significance: The number of protons defines the element. All atoms of a specific element have the same number of protons.

* Example: Carbon always has 6 protons, so its atomic number is 6.

2. Mass Number:

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

* Significance: It indicates the approximate mass of the atom (since protons and neutrons have roughly the same mass).

* Example: Carbon-12 has 6 protons and 6 neutrons, so its mass number is 12. Carbon-14 has 6 protons and 8 neutrons, so its mass number is 14.

Other ways to identify atoms:

* Isotopes: Atoms of the same element can have different numbers of neutrons, resulting in isotopes. Isotopes are identified by their mass number.

* Spectroscopy: This technique analyzes the light emitted or absorbed by atoms to determine their unique energy levels and identify the element.

* Nuclear magnetic resonance (NMR): This technique probes the magnetic properties of atomic nuclei to provide information about the structure and composition of molecules.

In summary:

The atomic number is the fundamental identifier of an atom, defining its element. The mass number provides additional information about the atom's composition and helps distinguish between isotopes of the same element. Other techniques like spectroscopy and NMR offer further insights into atomic structure and behavior.