Radioactive isotopes of lead

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What are the isotopes of radioactive elements?

Isotopes of an element are atoms of the same element with different atomic weights. Isotopes posts identical chemical properties because of their identical electronic structure. Isotopes of a particular element have the same number of protons but varying the number of neutrons inside the nucleus of an atom.
  1. When an Alpha particle emits from within the nucleus the mother element loss two units of atomic number and four units of mass number.
    If a radioactive element with mass number M and atomic number Z ejected an alpha particle the newborn element has mass number = (M - 4) and atomic number = (Z - 2).
  2. When a beta particle emits from the nucleus, the daughter element nucleus has an atomic number one unit greater than that of the mother element nucleus.
    If a radioactive element with mass number M and atomic number Z ejected a beta particle the newborn element has mass number the same and atomic number = (Z + 1).
₈₈Ra²²⁶ → ₈₈₋₂Rn²²²⁻⁴ + ₂He⁴(ɑ)
₈₈Ra²²⁶ → ₈₈Rn²²² + ₂He⁴(ɑ)
₉₀Th²³⁴ → ₉₁Pa²³⁴ + ₋₁e⁰(β)

Isotopes of lead and uranium

Uranium is the first discovered radioactive elements. Uranium in the 6th group or actinides of the periodic table with atomic number 92 and mass number 238. Uranium undergoes successive disintegration till the daughter elements become stable, non-radioactive isotopes of lead.
The mother element along with all the daughter elements down to the stable isotope of lead is called a radioactive disintegration series.

Radioisotopes of uranium - 235 and uranium - 238

Uranium - 238 disintegrate ultimately to an isotope of lead. The entire route involves eight alpha and six beta emissions to form the isotopes of lead with atomic number 82 and mass number 206.
₉₂U²³⁸ → ₈₂Pb²⁰⁶ + 8 ɑ + 6 β
Radioisotopes of lead - uranium -238 disintegration series
Radioisotopes of lead - uranium
The mass number of all the above disintegration products are given by (4n +2) where n = 59 for Uranium - 238. This disintegration series is known as (4n + 2) series.

Uranium - 235 or (4n+3) series starts with uranium - 235 and ends with the stable isotope of lead - 207. Seven alpha and four beta emissions in the entire route of the overall process,
₉₂U²³⁵ → ₈₂Pb²⁰⁷ + 7 ɑ + 4 β
Isotopes of lead-207 and uranium-235 in 4n + 3 series
Isotopes of lead-207 and uranium-235

Isotopes of thorium- 232 in radioactive disintegration

Thorium - 232 undergoes successive disintegration till the daughter elements become stable, non-radioactive isotopes of lead with mass number 208.
The entire route involves six alpha and four beta emission called the thorium- 232 disintegration series or 4n series.
₉₀Th²³² → ₈₂Pb²⁰⁸ + 6 ɑ + 4 β
Isotopes of thorium-232 and lead-208 in 4n + 3 series
Isotopes of thorium 232 and lead 208
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Periodic table and group displacement law

In 1913 Soddy proposed the law for the position of radioisotopes in the periodic table when the knowledge of atomic structure was still incomplete. extensive chemical studies on the disintegration products of different series preceded the announcement of this law.

When an alpha particle is emitted in a radioactive disintegration step, the product is displaced two places to the left in the periodic table but the emission of a beta particle results in a displacement of the product to one place to the right.

Soddy observed that more than one product belonging to the same group on the periodic table. He further established that the product elements belonging to the same group had identical chemical properties though their radioactivity's were different. Soddy coined the term isotope for such elements occupying the same place on the periodic table.

₉₀Th²³² → ₈₈Ra²²⁸ + ɑ → ₈₉Ac²²⁸ + β → ₉₀Th²²⁸ + β
₉₂U²³⁸ → ₉₀Th²³⁴ + ɑ → ₈₉Ac²³⁴ + β → ₉₂U²³⁴ + β


A study of the displacement law further reveals that when a parent radio element emits one alpha and two beta particles successively the product isotope occupies the same group in the periodic table with the parent element.

Uses of radioactive isotopes

Isotopes have been used in a variety filed like medicine, biology, agriculture, trace analysis, and many other fields. The uses of isotopes broadly classified under the heads,

Medicinal uses of isotopes

  1. Radioactive iodine-131 is used in the diagnosis and treatment of thyroid gland disorder. After drinking a solution of sodium iodide containing sodium-131. The radioactive iodine moves preferentially to the thyroid gland. The radiation or beta emission destroys the malignant cells without affecting the rest of the body.
  2. Cobalt-60 is a good gamma-ray emitter. Cobalt-60 used to inhibit the growth of malignant tissue in the treatment of cancer.
  3. For abnormality of the circulation of blood, a small amount of a sodium chloride solution labeled with sodium-24 a beta emitter used. Sodium chloride solution injected into a vein of the patient.

Radioactive isotopes of lead and uranium, the position of the radioisotopes in the periodic table, study medicinal uses of isotopes in chemistry

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