Title 13. NUCLEI.pdf ✅

In every atom, the positive charge and mass are densely concentrated at the center of the atom forming its nucleus. More than 99.9% mass of the atom is concentrated in the nucleus. Composition Of Nuclei the nucleus has two main components: protons and neutrons. The positively-charged entities are protons that are solely present inside the nucleus and neutrons are neutral in charge and do not carry any charge. Atomic number The total number of protons present inside a nucleus of an atom is called atomic number. The atomic number is denoted by the letter ‘Z’. Atomic mass The total combined number of neutrons and protons present inside a nucleus is called atomic mass. While calculating the mass of an atom, the mass of electrons should not be calculated; rather only the mass of neutrons and protons are taken into consideration. This is because the electrons are the lightest particles in a nucleus, and hence their mass is never considered while calculating atomic mass. The atomic mass number is also known as mass number. The atomic mass number is denoted by the letter ‘A’. It is the nearest integer value of mass represented in a.m.u. (atomic mass unit). 1 a.m.u. = 1 12 [mass of one atom of 6C12 atom at rest and in ground state] = 1.6603 × 10–27 kg 931.478 MeV/c2 mass of proton (mp) = mass of neutron (mn) = 1 a.m.u. No. of Protons, Electrons, nucleons and Neutrons in an Atom: (a) Number of protons in an atom = Z (b) Number of electrons in an atom = Z (c) Number of nucleons in an atom = A (d) Number of neutrons in an atom = N = A – Z Isotopes – The nuclides having the same atomic number (Z) but different mass number (A) are called isotopes. Isobars- The nuclides having the same mass number (A), but different atomic number (Z) are called isobars. Isotones- The nuclides having the same number of neutrons (A–Z) are called isotones. Mass – Energy Einstein showed that mass is another form of energy and one can convert mass-energy into other forms of energy, say kinetic energy and vice-versa. Einstein gave the famous mass- energy equivalence relation E = mc2 Here the energy equivalent of mass m is related by the above equation and c is the velocity of light in vacuum and is approximately equal to 3×108 m s Nuclear Binding Energy It is the minimum energy required to break the nucleus into its constituent particles. Or Amount of energy released during the formation of nucleus by its constituent particles and bringing them from infinite separation. CHAPTER – 13 NUCLEI NUCLEI