Isobars and Isotopes

Atoms of the same element with identical atomic numbers but different atomic masses are called isotopes. Conversely, elements with the same atomic mass but different atomic numbers are known as isobars. The chemical reactivity of isotopes is consistent since they have the same number of electrons. In contrast, isobars have varying numbers of electrons or protons, leading to differences in their chemical reactivity.

1.0Atomic composition 

The composition of an atom can be represented using the element symbol along with two numbers: the atomic number (Z) and the mass number (A).

• Atomic number (Z): The number of protons in the atom's nucleus determines the element.
• Mass number (A): The total number of protons and neutrons in the atom's nucleus.

The general notation for representing an atom is: _Z^A​X 

Where:

• X is the chemical symbol of the element.
• A is the mass number (the sum of protons and neutrons).
• Z is the atomic number (the number of protons).

For example:

• Carbon-12 can be written as ¹²₆C, where:
• • Z=6 (since carbon has 6 protons),
  • A=12 (the mass number, which is the total number of protons and neutrons).

This notation helps to uniquely identify the composition of atoms, distinguishing between isotopes of the same element (which have the same atomic number but different mass numbers).

2.0Isotopes

Isotopes are atoms with the same atomic number (the same number of protons) but different mass numbers due to varying numbers of neutrons. In simpler terms, isotopes of an element share the same number of protons but have a different number of neutrons.

For example, hydrogen has three isotopes:

• Protium (₁¹H): Contains 1 proton and 0 neutrons; makes up 99.985% of natural hydrogen.
• Deuterium (₁²D): Contains 1 proton and 1 neutron; makes up about 0.015% of natural hydrogen.
• Tritium (₁³T): Contains 1 proton and two neutrons; found in trace amounts on Earth.                                          

Other examples of common isotopes include:

• Carbon: ₆¹²C, ₆¹³C and ₆¹⁴C with 6, 7, and 8 neutrons, respectively, and always 6 protons.

• Chlorine: ₁₇³⁵Cl  and  ₁₇³⁵Cl, with 18 and 20 neutrons, respectively, and always 17 protons.

3.0Uses of Isotopes

In Medicine

• Cancer Treatment: Cobalt-60 emits gamma rays for radiotherapy.
• Skin Cancer: Treated with less penetrating radiation from Strontium-90 or Phosphorus-32.
• Heart Pacemaker: Plutonium-238 helps regulate heartbeats.
• Thyroid Treatment: Iodine-131 treats thyroid disorders.
• Dating Bones and Fossils: Carbon-14 measures age by its fraction in organic material.

In Agriculture

• Phosphorus Uptake in Plants: Traced using Phosphorus-32 in fertilisers.
• Photosynthesis and Protein Synthesis Studies: Using Carbon-14 as a radioactive tracer.

In Industry

• Leak Detection: Sodium-24 traces leaks in pipelines.
• Thickness Control: Krypton-85 radiation monitors plastic sheet thickness.
• Food Preservation: Cobalt-60 gamma rays sterilise food, preventing spoilage without altering taste or texture.

4.0Isobars

Isobars are atoms of different chemical elements with the same atomic mass, meaning the total number of protons and neutrons in their nuclei is the same. The atomic mass is the sum of protons and neutrons; each particle is called a nucleon. Despite having the same number of nucleons, isobars belong to different elements and thus have different atomic numbers.

According to the Mattauch isobar rule, when two adjacent elements in the periodic table have isotopes with the same mass number (isobars), one of these isotopes is likely to be radioactive. The first and last are stable if three isobars are found in sequence, while the middle isobar might undergo radioactive decay. A series of different isotopes with the same atomic mass is called an isobar series. 

For example, the elements ⁴⁰₁₆S, ⁴⁰₁₇Cl, ⁴⁰₁₈Ar, ⁴⁰₁₉K, and ⁴⁰₂₀Ca all have the same atomic mass (40) but different atomic numbers.

All these elements have a mass number of 40 but differ in the number of protons and neutrons in their nuclei.

5.0Uses of Isobars

• Nuclear Reactors: Uranium isobars are utilised as fuel.
• Goitre Treatment: Iodine isobars are effective in treating thyroid conditions.
• Cancer Treatment: Cobalt isobars are employed in radiotherapy for cancer.

6.0Comparison of Isotopes and Isobars