What are Isobars?

o Isobar is defined as the element which varies in their chemical property but has the same physical property.

o Consequently, it can be said that isobars are those elements which have a different atomic number and same mass number or nucleon number.

o Their chemical property differs because of the difference in the number of electrons that are present in their respective nuclei.

o The sum of the number of protons and neutrons together form the atomic mass of an element.

Atomic Mass = Protons +Neutrons

Protons and neutrons are together known as nucleons. Hence, it can be said that the number of nucleons that are present in the nucleus of an atom is always equal to the atomic mass of that atom. Thus, it will have the same number of nucleons.

o Isobars always have different atomic structure because of the difference in their respective atomic numbers.

o The number of neutrons present in a nucleus of an atom makes up the difference in the number of nucleons. Thus, isobar always have different chemical properties.

Isobars Examples

o The isobars iron and nickel. Iron and nickel have different atomic number 26 and 28 respectively. However, they have same mass number that is 58.

o Another example of isobars include; argon and calcium with different atomic numbers 18 and 20, respectively. But they have the same atomic mass that is 40.

o Moreover, sometimes there are series of an element that has same atomic mass.

o For instance, Cobalt (Co), Nickel (Ni), Copper (Cu), and Iron (Fe) have same atomic mass 64 but the atomic number of each differs.

oSome more examples are;

o ₁₈Ar⁴⁰ ₁₉K⁴⁰ ₂₀Ca⁴⁰ have same mass number 40, but different atomic number.

o ₃₂Ce⁷⁶, ₃₄Se⁷⁶ have same mass number 76, but different atomic number.

o ₁₁Na²⁴ ₁₂Mg²⁴ have same mass number 24, but different atomic number.

o ₂₆Fe⁵⁸, ₂₇Ni⁵⁸ have same mass number 58, but different atomic number.

o ₂₇Co⁶⁴ ₂₈Ni⁶⁴ have same mass number 64, but different atomic number.

Isotopes

o Atoms are made up of electrons, protons, and neutrons.

o The nucleus of an atom is made up of protons and neutrons and the electrons revolve around the nucleus.

o Isotopes are referred to as the atoms in which the number of neutrons varies and the number of protons is the same.

o From the above definition, it can be concluded that isotopes are defined as those elements that have the same atomic number and different mass number.

o For instance – isotopes of hydrogen: There are three isotopes of hydrogen and these are named as protium, deuterium, and tritium. All three of them that are mentioned above have the same number of protons, but the numbers of neutrons vary. In protium the number of neutrons is equal to zero, in deuterium, number of neutrons is equal to it is one and lastly in tritium, the number of neutrons is two.

Isotopes vs Isobars

Isobars	Isotopes
Isobars are referred to the atoms of different chemical elements having same atomic mass.	Isotopes are referred to as the atoms with the same number of protons but different numbers of neutrons.
The atomic masses are equal.	The atomic masses vary.
The physical properties are similar.	Physical properties are different.
Atomic numbers of elements are different.	Atomic numbers of elements are the same.
For Instances: ₁₁Na²⁴ ₁₂Mg²⁴ Have same mass number 24, but different atomic number.	For Instance:- Isotopes of Hydrogen- There are three isotopes of hydrogen and these are named as protium, deuterium, and tritium.