Radioactive Decay in Chemistry
Radioactivity cause the spontaneous decay of subatomic particles like alpha, beta, and gamma rays from the nucleus of very heavy types radioactive chemical elements or matter in the form of electromagnetic energy. This leads to the formation of new chemical elements by radioactive reactions of periodic table elements in chemistry or physics. The radioactive decay process continues until a stable nucleus of lead or one of the isotopes of lead formed. The nucleus of the radioactive decay elements composed of two types elementary particles like protons and neutrons which cause many nuclear reactions. Therefore, the ratio of neutron/proton or nuclear energy for binding is the main cause of natural or artificial radioactivity.
Radioactive decay definition and equation of the chemical element independent of the external condition like specific heat, pressure, pH, etc, and the environment. Radioactivity was also unaffected by chemical bonding or combination and the energy associated with radioactive disintegration = 109 calories per mole in nuclear science.
Nuclear stability and Neutron/Proton Ratio
In radioactivty, the neutron/proton or n/p ratio helps to predict the stability of the nucleus of radioactive elements in chemical science. In learning chemistry or nuclear chemistry, the below graph is obtained by plotting the atomic number of periodic table elements with the number of neutrons present in the nucleus of radioactive atoms.
The above plot of radioactivity shows that the actual n/p plot of stable isotopes breaks off from the hypothetical 1:1 plot around an atomic number 20. After atomic number 20, the line rises rather steeply. The number of protons increases inside the nucleus more and more neutrons are needed to minimize the proton-proton repulsion and thereby to add to nuclear stability. Therefore, neutrons are served as the binding materials inside the radioactive nucleus.
Cause of Nuclear Instability in Radioactivity
Stability or instability in radioactivity is connected with the pairing of nuclear spins or nuclear charge. The nucleus of an atom composed of two elementary particles like proton and neutron. Since all the elements in the periodic table are not radioactive. Therefore, the ratio of protons to neutrons of the nucleus is the factor responsible for radioactive emissions. Nuclear scientist studies these types of problems in radioactivity and connected the stability or instability of the nucleus with the radioactive pairing energy of spin pairing.
- Radioactive nuclei with an even number of protons and even number of neutrons are the most stable isotopes of elements. Here even number leads to spin pairing but an odd number leads to unpaired spins.
- Radioactive nuclei with either protons or neutrons number odd are slightly less stable than even-numbered ones.
- In radioactivity, the least stable radioactive isotopes formed by odd numbers of protons and an odd number of neutrons.
Problem: Why gold-197 is non-radioelement but radium-226 is radioactive substances?
Answer: The number of neutron and protons 188 and 79 respectively in an isotope of gold-197. The neutron to proton ratio = 118/79 =1.49, which is less than 1.5. Therefore the radioactive isotope of a gold-197 stable. The number of neutron and protons 138 and 88 respectively in isotopes radium-226. Hence the neutron to proton ratio = 226/88 = 1.57, which is less than 1.5. Therefore, the radioactive isotope of a radium-226 stable.
Neutron to Proton Ratio too High
Isotopes with too many neutrons in the nucleus can attain greater stability if one of the decays of the neutron to the proton in a nuclear reaction. Such disintegration leads to the electron emission or beta emission inside the radioactive nucleus. The neutron/proton ratio is high when the mass number of radioactive isotopes greater than the average atomic weight.
0n1 → 1H1 + -1e0 (electron)
Radioactive Carbon and Iodine
The neutron/proton ratio for stable radioactive isotopes of carbon-12 = 1.0 with six protons and six neutrons. But for radioactive carbon-14 = 1.3 with eight neutrons and six protons. Therefore, caron-14 will show radioactity by emit beta rays from the nucleus. Similarly, the neutron/proton ratio for iodine-127 and iodine-133 = 1.4 and 1.5 respectively. Therefore, iodine-133 is a beta emitter largely uses in nuclear medicine.
6C14 → 7N14 + -1e0
53I133 → 54Xe133 + -1e0
Electron Capture Reaction in Radioactivity
A nucleus deficient in neutrons will tend to attain nuclear stability by converting one of its protons to a neutron and this will be achieved either by the emission of a position or by the capture of an electron. Positron emission occurs with light type radioactive isotopes of the elements of a low atomic number. Nitrogen-13 and iodine-121 has the neutron/proton ratio = 0.86 and 1.3 respectively. Therefore, these radioactive elements gain their nuclear stability by positron emission or electron capture reaction. But the electron capture reaction not alike with electron affinity because radioactivity is the nuclear phenomena.
1H1 → 0n1 + +1e0 (positron)
7N13 → 6C13 + +1e0
53I121 → 52Te121 + +1e0
Orbital Electron Capture Reaction
Orbital electron capture in radioactivity occurs with too light isotopes of radioactive elements of relatively high atomic numbers. For such elements, the nucleus captures an electron from the nearest energy levels or orbitals. Therefore, the orbital electron capture reaction in radioactivity changes one proton to the neutron.
37Rb82 + -1e0 → 36Kr82
79Au194 + -1e0 → 78Pt194
The effect of nuclear transformation resulting from the electron capture is the same as that with the positron emission reaction in radioactive transformation. In both cases, the proton in the nucleus converted into the neutron. The energy emission in such radioactive nuclear transformation given the electromagnetic spectrum like x-rays with specific wavelengths.
Unit of Radioactivity Measurement
Radioactivity obeys the first-order decay reaction in chemical kinetics define by counting the number of radioactive particles emitted in a given time. The number of disintegration per second expressed the term natural radioactivity. One gram of radium undergoes about 3.7 × 1010 disintegrations per second. In radioactivity, the quantity of 3.7 × 1010 disintegrations per second is called one curie, which is the older unit of radioactive emission. Here, millicurie and microcurie respectively correspond to 3.7 × 107 and 3.7 × 104 disintegrations per second in radioactivity. Therefore, the radioactive phosphorus-32, the beta – emitter, has radioactivty of 50 millicuries per gram means that for every gram of phosphorus-32 or phosphorus-32 compound molecule undergoes 50 × 3.7 × 107 decay taking place per second.
SI unit of radioactivity is Becquerel or simply Bq. Becquerel in radioactivty has expressed by one disintegration per second in nuclear chemistry or science. Therefore, 3.7 × 1010 Bq = 1 curie. Rutherford or simply Rd is the practical unit of radioactivity.