Structure of Atom

ISOTOPES

• Isotopes are defined as the atoms of the same element having the same atomic number but different mass numbers.
• Isotopes of chlorine: The two isotopes of chlorine can be written as:

• Isotopes of Hydrogen: The three isotopes of hydrogen can be written as:

• Hydrogen element has three isotopes: protium, deuterium and tritium, having the same atomic number of 1 but different mass numbers of 1, 2 and 3 respectively.

• All the Isotopes of an Element Have Identical Chemical Properties
• Since all the isotopes of an element have identical electronic configuration containing the same number of valence electrons, therefore, all the isotopes of an element show identical properties.

• The Physical Properties of the Isotopes of an Element are Different
• Since the masses of the isotopes of an element are slightly different, therefore, the physical properties of the isotopes of an element are slightly different.

RADIOACTIVE ISOTOPES

• The isotopes which are unstable due to the presence of extra neutron in their nuclei and emit various types of radiations are called radioactive isotopes.
• The high energy radiations emitted by radioactive isotopes are harmful to human beings.

• Application of Radioactive Isotopes

1. Production of Energy: Radioactive isotopes are used as a fuel in nuclear reactors of nuclear power plants for generating electricity.

Uranium-235 isotope is used as a fuel in the reactors of nuclear power plants for generating electricity.

2. Treatment of Diseases: Radioactive isotopes Arsenic-74 are used as ‘tracers’ in medicine do detect the presence of tumors and blood clots, etc., in the human body.

3. Treatment of Cancer: Radioactive isotopes Cobalt-60 are used in the treatment of cancer.

4. Isotopes of Iodine-131 are used to determine the activity of thyroid gland which helps in the treatment of diseases like goitre.

5. Radioactive isotopes are used in industry to detect the leakage in underground oil pipelines, gas pipelines and water pipes.

ISOBARS

• Isobars are the atoms of different elements having different atomic numbers but the same mass number (or some atomic mass).
• The difference in the chemical property is due to the difference in the number of electrons. It has same atomic mass but different atomic number because an additional number of neutrons compensates the difference in the number of nucleons.
• Therefore
  $\mathrm{Ne}_{10}^{22} \mathrm{and} \mathrm{Na}_{11}^{22}$

   are isobars

• Similarly
  $\mathrm{Ar}_{18}^{40} \mathrm{and} \mathrm{Ca}_{20}^{40}$

   are isobars.