Question

What happen to the atomic number of an element, when it emits an $\alpha -$particle ?

Answer 1

1. A radioactive nucleus emit an $\alpha -$particles, its mass number decreases by$4units$ and its atomic number decreases by $2units$.
2. Because $\alpha -$particles have mass number $4$and atomic number is $2$.
3. Consider the radioactive nucleus $X$ having mass number $A$ and atomic number $Z$ emit $\alpha -$particles to transform into nucleus$Y.$
4. representation of nuclear equation as given below.

${}_Z{}^{A}X\to {}_{Z-2}{}^{A-4}Y+{}_2{}^{4}He+energy$

Hence, a radioactive element emits $\alpha -$particles its atomic number decreases by $2units$ and its mass number decreases by$4units$.