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Different kinds of matter show different behaviours; you might have observed that matter like camphor disappears when placed in an open environment. On the other hand, metals like gold and silver remained unchanged for quite a long time. Do you know the reason behind it? Every matter consists of different atoms and every atom exhibits different behaviours. The chemical reactivity of an element depends on the structure of the atom.
Some atoms have the same atomic number but a different mass number. Such kinds of atoms are known as isobars. Let us know about the isobars through this topic.
Composition of atom
The atomic structure includes three subatomic particles arranged systematically. These are:
- Electrons: Electrons are negatively charged particles that revolve around the nucleus. The mass of electrons is so low that we take it to be negligible mass.
- Protons: The protons are the positive charge that lies in the atom’s nucleus along with the neutrons. Protons have significant mass.
- Neutrons: Neutrons are chargeless particles that have mass. It lies in the centre of the atom in the nucleus.
Atomic number and Mass Number
An atom is made up of parts photons, electrons and neutrons. These elements are responsible for determining the atomic mass and number.
1. Atomic number
Total number of photons present in the nucleus of atoms determines the atomic number of the atoms. The atomic number of atoms is denoted by “Z”. For example, for Hydrogen, its atomic number is one because there is only one proton present in the nucleus of Hydrogen. Similarly, the atomic number of helium is 2, which denotes that there are 2 protons in the atomic structure of helium.
2. Mass number
The mass number of an element is denoted by the alphabet ‘A’. The sum of the total number of protons and neutrons gives us the mass number of a particular element. It is also known as nucleons.
Atomic number, mass number and symbol is written in the following way-
For example, Nitrogen is written as 714N . Here, 7 denotes the atomic number, 14 is the mass number, and “N” is the atomic symbol for Nitrogen.
Isobars
The atoms or elements with different atomic numbers, but the same number of nucleons are known as isobars. The term isobars were first used in 1918 by Alfred Walter Stewart. It has been derived from the Greek words’ iso’ and ‘baros’. ‘Iso’ means equal, and ‘baros’ means weight.
Due to different atomic numbers, they have different chemical properties. Examples of isobars are 40Cl and 40S. Here, sulphur and chlorine are different elements and thus have different atomic numbers. But the mass number of sulphur and chlorine are the same: 40.
The Atomic numbers of Sulphur and Chlorine are 16 and 17. Therefore, their proton number will also be 16 and 17. Now they both have the same mass number. The mass number equals the number of protons and neutrons.
For Sulphur:
Mass number = No. of Proton + No. of Neutron
40 = 16 + No. of Neutron
No. of Neutron = 40 – 16
No. of Neutron = 24
For Chlorine:
Mass number = No. of Proton + No. of Neutron
40 = 17 + No. of Neutron
No. of Neutron = 40 – 17
No. of Neutron = 23
Thus, for Sulphur and Chlorine, the number of neutrons is also different. Thus, in isobars, the number of neutrons and a number of protons are different, but their sum is the same.
There are significant uses of isobars. For example, uranium isobars are used in nuclear reactors. Isobars of iodine are used to treat goitre, whereas isobars of cobalt are used in cancer therapy.
Difference between isotopes and isobars:
Isotopes | Isobars |
Isotopes are elements with the same atomic number but a different mass number. | Isobars are elements with different atomic numbers but the same mass number. |
Isotopes belong to the same element. | Isobars belong to different elements. |
They have the same number of electrons and protons but different numbers of neutrons. | They have different numbers of electrons, neutrons and protons. |
They have the same chemical properties. | They have different chemical properties. |
Examples: Protium1H, Deuterium 2H and tritium 3H are the isotopes of Hydrogen. | Chlorine 40Cl and Sulphur 40S are examples of isobars. |
Conclusion
As per the Dalton atomic theory, the atoms were assumed to be indivisible particles. But later, the discovery of electrons, protons and neutrons proved the theory wrong. It was found that atoms can be divided into three subatomic particles: electrons, protons and neutrons.
The arrangement of these subatomic particles led to the discovery of isotopes and isobars. Isotopes are atoms with the same atomic number but different mass numbers. At the same time, isobars are atoms with the same mass number.
