Isotopes

Definition of Isotopes

Isotopes are atoms of the same element that have the same number of protons but a different number of neutrons. This means they have the same atomic number but different mass numbers.

Because isotopes have the same number of protons, they belong to the same element, but the difference in neutrons causes variation in their mass.

Examples of Isotopes

Common examples of isotopes include:

• Carbon-12 and Carbon-14: Both are isotopes of carbon with 6 protons, but Carbon-12 has 6 neutrons while Carbon-14 has 8 neutrons.
• Hydrogen isotopes:
  • Protium (most common hydrogen isotope) with 0 neutrons
  • Deuterium with 1 neutron
  • Tritium with 2 neutrons (radioactive)

These isotopes have the same chemical behaviour but differ in mass and some physical properties.

Properties of Isotopes

Isotopes of an element share the same chemical properties because chemical reactions depend on the number of protons and electrons, which remain unchanged.

However, isotopes have different physical properties due to their different masses. For example, heavier isotopes may have different densities or rates of diffusion.

Each isotope has a unique mass number, which is the total number of protons and neutrons in the nucleus. For example, Carbon-12 has 6 protons and 6 neutrons, so its mass number is 12.

For instance, Carbon-12 and Carbon-14 both react chemically in the same way, but Carbon-14 is radioactive and heavier due to its extra neutrons.

Uses of Isotopes

Isotopes have important practical uses. Note that not all isotopes are radioactive; some are stable.

• Carbon-14 dating: Carbon-14 is a radioactive isotope used to date ancient organic materials by measuring how much Carbon-14 remains.
• Medical tracers: Radioactive isotopes can be used to trace the movement of substances in the body, helping diagnose conditions.
• Radioactive isotopes in treatment: Some isotopes are used to treat diseases, such as cancer, by targeting and destroying harmful cells.

Learning Example

Example: Explain why Carbon-12 and Carbon-14 have the same chemical properties but different physical properties.

Both isotopes have 6 protons, so they have the same number of electrons and react chemically in the same way. However, Carbon-14 has 2 more neutrons than Carbon-12, making it heavier and radioactive, which changes its physical properties like mass and stability.