Atoms, Elements and Compounds – Isotopes
What is an Isotope?
Isotopes are different atoms of the same element that have the same number of protons (\$Z\$) but a different number of neutrons (\$N\$). The total number of protons and neutrons is called the mass number (\$A\$).
Think of a family where everyone has the same last name (the element) and the same number of parents (protons), but they may have different heights (neutrons). Each family member is still part of the same family, just a bit taller or shorter.
Why Does It Matter?
- Isotopes have different physical properties (e.g., stability, radioactivity).
- They are used in dating (radiocarbon dating) and medicine (diagnostic imaging).
- Understanding isotopes helps explain why two atoms of the same element can behave differently.
Examples of Isotopes
| Element | Isotope | \$Z\$ (Protons) | \$N\$ (Neutrons) | \$A\$ (Mass Number) |
|---|
| Carbon (C) | Carbon‑12 | 6 | 6 | 12 |
| Carbon (C) | Carbon‑13 | 6 | 7 | 13 |
| Carbon (C) | Carbon‑14 | 6 | 8 | 14 |
Exam Tip: Identifying Isotopes
- Write the mass number (\$A\$) first, followed by the element symbol. Example: \$^{14}\text{C}\$.
- Remember that the atomic number (\$Z\$) is the same for all isotopes of an element.
- When a question asks for the neutron count**, subtract \$Z\$ from \$A\$ (\$N = A - Z\$).
- Use the periodic table** to check the atomic number quickly.
Quick Facts for Revision
- Protons (\$Z\$) determine the identity of the element.
- Neutrons (\$N\$) add mass and can affect stability.
- Isotopes of the same element have the same chemical behaviour but can differ in physical properties.
- Stable isotopes are non‑radioactive; unstable ones decay over time.
Good luck with your studies! Remember, isotopes are just different “versions” of the same element, like different models of the same car brand. 🚗🔬📚