(a) Define atomic number and mass number.

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The atomic number of an element is defined as the number of protons in the nucleus of an atom of that element. It is denoted by the symbol \( Z \).

The atomic number determines the identity of an element and its position in the periodic table. For example, hydrogen has an atomic number of 1, meaning it has one proton.

The mass number of an atom is the total number of protons and neutrons in its nucleus. It is denoted by the symbol \( A \).

The mass number is calculated by adding the number of protons (atomic number) and the number of neutrons in the atom. For example, if an atom has 6 protons and 6 neutrons, its mass number is 12.

While the atomic number is unique to each element, the mass number can vary among atoms of the same element due to the presence of isotopes, which are atoms with the same number of protons but different numbers of neutrons.

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Atomic Number

The atomic number is the number of protons found in the nucleus of an atom. It uniquely identifies an element and determines its position on the periodic table. For example, hydrogen has an atomic number of 1, indicating it has one proton. The atomic number also influences the chemical properties of the element.

Mass Number

The mass number is the total number of protons and neutrons in an atom's nucleus. It is not the same as atomic mass, which is a weighted average of all isotopes of an element. For instance, carbon has a mass number of 12, which means it typically has 6 protons and 6 neutrons. The mass number helps in identifying isotopes of an element.

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different mass numbers. For example, carbon-12 and carbon-14 are isotopes of carbon, with mass numbers of 12 and 14, respectively. Isotopes can exhibit different physical properties and stability, influencing their applications in fields like medicine and archaeology.