Chapter 17 - Radioactivity and Nuclear Chemistry - Exercises - Problems - Page 638: 65

After filling the blanks, the partial decay series is as follows:

Look at the 1st equation. Here, Pu-241 (Atomic number 94) is converted to Am-241 (Atomic number 95). Hence, Atomic number is increased by 1 unit but mass number does not change. Therefore, it is clear that one beta is emitted from Pu-241. So, the blank will be fulfilled by writing beta in the form of symbol (write symbol 'e' and on the left subscript of 'e', write -1 and on left superscript write 0). Now, look at the 2nd equation. Here, Am-241 is converted to Np-237 (Atomic Number 93). So, we can see that atomic number is decreased by (95-93)= 2 unit and mass number is decreased by (241-237) =4 unit. Clearly, an alpha particle is emitted from Am-241 which can be denoted by chemical symbol of Helium atom (because alpha particle is equivalent to one He atom). So, the blank will be fulfilled by writing chemical symbol of He on the right side of the equation. In the 3rd equation, we can see that Np-237 undergoes alpha decay because on the right side of the equation we see there is He atom present. After alpha decay, atomic number is decreased by 2 units. So, the atomic number of the daughter nuclide will be (93-2)= 91 and mass number is decreased by 4 units. So, the mass number of daughter nuclide will be (237-4) = 233. Therefore, the daughter nuclide will be Pa-233 (Atomic number of Pa is 91) which is written in the form of chemical symbol on the right side of the equation. In the 4th equation, we can see that the daughter element (element on the right side of the equation) is U-233 (atomic number 92) and a beta particle is emitted. After beta emission, atomic number is decreased by 1 unit and mass number remains same. So, before beta emission, the parent nuclide has the same mass number as the daughter element but atomic number will be less than 1 unit. Hence, the atomic number of parent nuclide is 92-1 = 91. The element having atomic number 91 is Pa which is written in the form of chemical symbol on the right side of the equation.