Home Preparation for National Talent Search Examination (NTSE)/ Olympiad
Chapter : 4. Structure Of Atoms
Relationship between mass number and atomic number
Relationship between mass number and atomic number : Mass number = No. of protons + No. of neutrons Mass number = Atomic number + No. of neutrons Example. The atomic nucleus of an element has mass number 23 and number of neutrons 12. What is the atomic number of the element? Solution. We know that Mass No. = No. of protons + No. of neutrons 23 = No. of protons + 12 No. of protons = 23 – 12 = 11 Now, Atomic No. = No. of protons = 11. Example. Calculate the number of : (i) electrons (ii) protons (iii) neutrons and (iv) nucleons in Solution. Mass No. = 39 Atomic No. = 19 (i) We know that atomic No. = No. of protons = No. of electrons No. of electrons = 19 (ii) No. of protons = 19 (iii) Mass No. = No. of neutrons + No. of electrons No. of neutrons = mass number – No. of protons = 39 – 19 = 20 (iv) Nucleons = No. of protons + No. of neutrons = 19 + 20 = 39