Isobars
Explanation
The classification of atoms is based on the composition of their nuclei, specifically the number of protons (Atomic Number, Z) and the number of neutrons. The sum of protons and neutrons constitutes the Mass Number (A).
- Isobars: These are atoms of different chemical elements that possess different atomic numbers but the same mass number. Since the atomic number determines the element's identity, isobars belong to different elements and exhibit different chemical properties.
Example: Argon ($_{18}^{40}\text{Ar}$) and Calcium ($_{20}^{40}\text{Ca}$) are isobars because both have a mass number of 40, despite having atomic numbers of 18 and 20, respectively. - Isotopes: These are atoms of the same element having the same atomic number but different mass numbers (due to a difference in the number of neutrons).
Example: Protium ($_{1}^{1}\text{H}$), Deuterium ($_{1}^{2}\text{H}$), and Tritium ($_{1}^{3}\text{H}$). - Isomers: In the context of nuclear physics, nuclear isomers are atoms with the same atomic number and same mass number but different energy states (metastable states). In general chemistry, isomers refer to molecules with the same chemical formula but different structural arrangements.
- Allotropes: These are different structural forms of the same element in the same physical state. They differ in the arrangement of atoms.
Example: Diamond and Graphite are allotropes of Carbon.
Key Takeaway: Isobars are characterized by having the same total number of nucleons (protons + neutrons) but a different number of protons, meaning they represent different elements with the same atomic mass.