Nuclei: Nucleus, Isotopes, Radioactivity, Nature of Binding Energy (For CBSE, ICSE, IAS, NET, NRA 2022)

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Nucleus (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: Atomic nucleus, the very dense central region of an atom. Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell՚s DNA

Cell Nucleus Anatomy


  • An atom consists of the nucleus which is positively charged.
  • Atomic radius is larger than the nucleus՚s radius. The mass of an atom is focused on the nucleus.
  • The nucleus can send out instructions to various other cell parts so that they perform their functions.
  • An atom consists of neutrons which have the same mass as protons.
  • Protons and neutrons are bound with each other with a nuclear force.
  • Energies present in nuclear activities is much larger than that of a chemical process.
  • The nucleus is important and it has its own membrane that surrounds it.


Six Protons of Isotopes
  • When the nuclides have the same number of atoms but a different number of neutrons then it is termed as isotopes.
  • Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom.


Radioactivity: Law of Radioactive Decay
  • The nuclei of certain elements give out rays and each representing as helium nuclei, electrons, and electromagnetic radiation respectively
  • Radioactivity is the sign of instability of the nuclei.

Why Fusion Requires High Temperature?

The nuclei which are light must have sufficient initial energy to overpower the Coulombs law between electrical charges having a potential barrier which is only possible in high temperatures.

Nature of Binding Energy

  • This shows that nuclear reactions which are exothermic in nature are possible in which when a heavy nucleus undergoes fission or two lighter nuclei fuse together to form nuclei with medium mass.
  • Nuclear binding energy is the minimum energy that would be required to disassemble the nucleus of an atom into its component parts

What is the Density of Nucleic Matter?

  • Nuclear density is the density of the nucleus of an atom, averaging about
  • The mass density of atoms does not make it capable of depending upon the size of the nucleus.
  • The descriptive term nuclear density is also applied to situations where similarly high densities occur, such as within neutron stars.