Atomic number, mass number, and net charge are important concepts in atomic and nuclear physics. Here are their definitions and the differences between them:
Atomic Number: The atomic number (Z) represents the number of protons in the nucleus of an atom. It uniquely identifies the element. For example, hydrogen has an atomic number of 1, helium has an atomic number of 2, and so on. In a neutral atom, the atomic number also gives the number of electrons surrounding the nucleus.
Mass Number: The mass number (A) is the sum of protons and neutrons in the nucleus of an atom. It represents the total number of nucleons (protons and neutrons) present in the nucleus. Unlike the atomic number, the mass number can vary among atoms of the same element. Isotopes of an element have the same atomic number but different mass numbers. For example, carbon-12 (C-12) and carbon-14 (C-14) are isotopes of carbon with mass numbers of 12 and 14, respectively.
Net Charge: The net charge of an atom or ion indicates the overall electrical charge due to the imbalance between the number of protons and electrons. Protons carry a positive charge, while electrons carry a negative charge. In a neutral atom, the number of protons equals the number of electrons, resulting in a net charge of zero. However, if an atom gains or loses electrons, it becomes an ion and acquires a net positive or negative charge, respectively. For example, if an atom loses one electron, it becomes a positively charged ion, often denoted as a cation. Conversely, if an atom gains an electron, it becomes a negatively charged ion, known as an anion.
To summarize, the atomic number gives the number of protons (and electrons) in an atom, the mass number represents the sum of protons and neutrons, and the net charge reflects the overall electrical charge resulting from the imbalance of protons and electrons in an atom or ion.