Chemistry · Chapter 21
Study notes aligned to the official NEB syllabus.
Nuclear chemistry deals with changes in the nucleus of an atom, in contrast to ordinary chemistry which involves only the outer electrons. Nuclear changes release enormous energy (millions of times that of chemical reactions), because they convert a small amount of mass into energy according to Einstein's relation $E = mc^2$.
Radioactivity is the spontaneous emission of radiation ($\alpha$, $\beta$ or $\gamma$ rays) from the unstable nucleus of certain elements, discovered by Henri Becquerel (1896) and studied by Marie and Pierre Curie. A nucleus is unstable when its neutron-to-proton ratio lies outside the stable band.
The three natural radiations:
| Ray | Nature | Charge | Penetrating power |
|---|---|---|---|
| Alpha ($\alpha$) | helium nucleus $\ce{^{4}_{2}He}$ | $+2$ | low (stopped by paper) |
| Beta ($\beta$) | fast electron $\ce{^{0}_{-1}e}$ | $-1$ | medium (stopped by aluminium) |
| Gamma ($\gamma$) | high-energy electromagnetic wave | $0$ | very high (stopped by thick lead) |
$$\ce{^{27}{13}Al + ^{4}{2}He -> ^{30}{15}P + ^{1}{0}n}$$
The $\ce{^{30}_{15}P}$ formed is radioactive.
Nuclear chemistry deals with changes in the nucleus of an atom, in contrast to ordinary chemistry which involves only the outer electrons. Nuclear changes release enormous energy (millions of times that of chemical reactions), because they convert a small amount of mass into energy according to Einstein's relation .
Radioactivity is the spontaneous emission of radiation (, or rays) from the unstable nucleus of certain elements, discovered by Henri Becquerel (1896) and studied by Marie and Pierre Curie. A nucleus is unstable when its neutron-to-proton ratio lies outside the stable band.
The three natural radiations:
| Ray | Nature | Charge | Penetrating power |
|---|---|---|---|
| Alpha () | helium nucleus | low (stopped by paper) | |
| Beta () | fast electron | medium (stopped by aluminium) | |
| Gamma () | high-energy electromagnetic wave | very high (stopped by thick lead) |
The formed is radioactive.