24.116 CP - Chemistry: Molecular Nature Of Matter And Change

Question

Which isotope in each pair is more stable? Why? 

(a) ${}_{\text{55}}{}^{\text{140}}\text{Cs}$or  ${}_{\text{55}}{}^{\text{133}}\text{Cs}$                              (b)${}_{\text{35}}{}^{\text{79}}\text{Br}$ or  ${}_{\text{35}}{}^{\text{78}}\text{Br}$

(c) ${}_{\text{12}}{}^{\text{28}}\text{Mg}$or ${}_{\text{12}}{}^{\text{24}}\text{Mg}$                                (d) ${}_{\text{7}}{}^{\text{14}}\text{N}$or ${}_{\text{7}}{}^{\text{18}}\text{N}$

Step-by-Step Solution

Answer

a) ${}_{\text{55}}{}^{\text{133}}\text{Cs}$is more stable isotope

b) ${}_{\text{35}}{}^{\text{79}}\text{Br}$is more stable isotope

c) ${}_{\text{12}}{}^{\text{24}}\text{Mg}$is more stable isotope

d) ${}_{\text{7}}{}^{\text{14}}\text{N}$is more stable isotope

Step 1: Definition of Isotope

Isotopes are chemical elements that have the same number of protons and electrons but differ in the number of neutrons they have.

Step 2: Determining more stable isotope

a) ${}_{\text{55}}{}^{\text{133}}\text{Cs}$ 

In comparison to${}_{\text{55}}{}^{\text{133}}\text{Cs}$ , the N/Z ratio ofdata-custom-editor="chemistry" ${}_{\text{55}}{}^{\text{140}}\text{Cs}$ is higher.

Step 3: Determining more stable isotope

b) ${}_{\text{35}}{}^{\text{79}}\text{Br}$

In comparison to ${}_{\text{35}}{}^{\text{79}}\text{Br}$, this isotope has an even number of neutrons.

Step 4: Determining more stable isotope

c) ${}_{\text{12}}{}^{\text{24}}\text{Mg}$

Its N/Z ratio is equal to one.

Step 5: Determining more stable isotope

d) ${}_{\text{7}}{}^{\text{14}}\text{N}$

Its N/Z ratio is equal to one.