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N – Neutron Number = Number of Neutron

A – Atomic Mass Number = Z + N = Total number of protons and neutrons

So now the elements of the periodic table had a new form of representation;

For example, the nucleus of a Uranium atom is represented by a 23592 U which means that one atom of Uranium 235 contains 235 nucleons, of which 92 are protons and the rest 143 are neutrons.

Isotopes, Isobars and Isotones

Isotopes are variants of a particular element with different a different number of neutrons. For example, the two isotopes of Uranium are, 23592 U and 23992 U. You will see here that the number of protons is the same in both the isotopes but they contain 143 and 147 neutrons respectively. The presence of an extra neutron significantly changes the behavior of that particular atom. There are two different types of isotopes, stable and radioactive. Stable isotopes are one that can exist in its free state without breaking down spontaneously. Radioactive isotopes are ones that are too unstable to sustain itself and they spontaneously break down into two lighter daughter elements with the emission of particles such as alpha, beta and gamma rays.

Isobars are elements that have the same number of nucleons (sum of protons and neutrons). The series of elements with 40 Mass number serves as a good example; 4016S, 4017Cl, 4018Ar, 4019K, and 4020Ca. The nucleus of all the above mentioned elements contain the same number of particles in the nucleus but contain varying numbers of protons and neutrons.

Isotones are atoms that have the same neutron number but different proton number. For example, 3616S, 3717Cl, 3818Ar, 3919K and 4020Ca are all isotones of 20 since they all contain 20 neutrons.

Nuclear energy and Radioactivity relies on the unstable isotopes of heavy elements to tap the explosive power of the nucleus. The discovery of one fundamental particle unlocked such amazing doors for humanity! Come fall in love with learning at BYJU’s.


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