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Neutron is a fundamental particle which is an essential constituent of all nuclei except that of hydrogen atom. It was discovered by Chadwick. A free neutron outside the nucleus is unstable and decays into proton and electron.
  • The charge of neutron: It is neutral
  • The mass of neutron: 1.6750 × 10–27kg
  • Its spin angular momentum: 106230.png
  • Its magnetic moment: 9.57 × 10–27 J/T
  • Its half life: 12 min
  • Penetration power: High
  • Neutrons are of two types: slow neutron and fast neutron. Both are fully capable of penetrating a nucleus and causing artificial disintegration.

Types of nuclei

The nuclei have been classified on the basis of the number of protons (atomic number) or the total number of nucleons (mass number) as follows:
Isotopes The atoms of an element having same atomic number but different mass number are called isotopes. All isotopes have the same chemical properties. The isotopes of some elements are the following: 106237.png 106243.png 106263.png
Isobars The nuclei which have the same mass number (A) but different atomic number (Z) are called isobars. Isobars occupy different positions in periodic table so all isobars have different chemical properties. Some of the examples of isobars are 1H3 and 2He3, 6C14 and7N14, 8O17 and 9F17.
Isotones The nuclei having equal number of neutrons are called isotones. For them both the atomic number (Z) and mass number (A) are different, but the value of (AZ) is same. Some examples are 4Be9 and 5B10, 3C13 and 7N14, 8O18 and 9F19, 3Li7 and 4Be8, 1H3 and 2He6.

Size of nucleus

Nuclear radius Experimental results indicate that the nuclear radius is proportional to A1/3, where A is the mass number of nucleus i.e., 106289.png where R0 = 1.2 × 10–15m = 1.2 fm.
Nuclear volume The volume of nucleus is given by 106299.png
Nuclear density Mass per unit volume of a nucleus is called nuclear density.
where m = average of mass of a nucleon (= mass of proton + mass of neutron = 1.66 × 10–27 kg) and mA = Mass of nucleus
⇒ 106311.png

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