NEET Foundation Chemistry Notes For  Chapter 4 Isotopes

NEET Foundation Chemistry Notes For  Chapter 4 Structure Of Atom Isotopes

Isotopes are the atoms having same number of protons, but different numbers of neutrons, i.e., they have different atomic weights. Isotopes are different forms of a single element. Till now, there are 275 isotopes of the 81 stable elements and over 800 radioactive isotopes have been discovered which are both natural and synthetic. Every element which is present on the periodic table has multiple isotope forms.

The chemical properties of isotopes of a single element are nearly identical. Except the isotopes of hydrogen, as the number of neutrons has a significant effect on the size of the hydrogen nucleus. Physical properties of isotopes are different from each other, as it depends on mass.

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So, Isotopes have same atomic number but different mass number and occur due to the presence of different number of neutrons in elements which have a same atomic number as mass number is the sum of the number of neutrons and protons. Not all elements have isotopes.

The isotopes of hydrogen are protium (has one proton and no neutrons) and that of deuterium (has one proton and one neutron) and tritium (has one proton and two neutrons). The chemical properties of isotopes are same as they have same number of protons and hence same number of electrons.

NEET Foundation Chemistry Notes For  Chapter 4 Isotopes

To Indicate Isotopes

  • List the mass number of an element after its name or element symbol.
    For example, an isotope with 6 protons and 6 neutrons is carbon-12 or C-12. An isotope with 6 protons and 7 neutrons is carbon-13 or C-13.
  • The mass number may be given in the upper left side of an element symbol.
    For example, the isotopes of hydrogen may be written as: 11H, 21H, 31H

Isotopes of hydrogen

NEET Foundation Chemistry Structure Of Atom Isotopes of hydrogen

Example: Carbon-12 and Carbon-14 are isotopes of carbon, one with 6 neutrons and one with 8 neutrons. Carbon-12 is a stable isotope, while carbon-14 is a radioactive isotope (radioisotope).

Radioactive Isotope

It has an unstable combination of protons and neutrons, and that is why they have an unstable nucleus. Because these are unstable, hence they undergo decay and emit alpha, beta and gamma rays. Radioactive isotopes can be useful in different industries, such as food, agriculture, archaeology and medicine.

Fractional Mass Number

The atomic masses of most elements are fractional as there may be a mixture of isotopes of different masses, so the fractional atomic masses arise because of this mixture.

\(\text { Average mass }=\frac{\text { total mass of all atoms }}{\text { number of atoms }}\)

Application of Isotopes

  • The identification of primary and secondary food sources.
  • Tracing nutrient and mineral uptake by plants and animals.
  • Determining the relative importance of plants and microbes to greenhouse gas emissions from soil.
  • Measuring environmental stressors by monitoring plant uptake of CO2 and/or water.
  • Tracing the sources of catchments waters.
  • Isotope of Uranium 23592Ur, is used in nuclear plants to generate electricity.
  • The use of isotopes is very common in Isotopic Labelling. Unusual isotopes are used as tracers or markers in chemical reactions.
  • Radiations of radioactive isotopes can be used for detecting various reactants, rates, and so on in chemistry.
  • Isotopes are used in Radiometric Dating, similar to Radio Isotopic Labelling or Radiocarbon Dating to study chemical processes by using naturally occurring isotopic tracers.
  • Isotopic substitution can be used to determine the mechanism of a reaction using Kinetic Isotope Effect.
  • Isotopes exhibit different nuclear properties as they have varied numbers of neutrons. This also affects their physical properties.
  • Spectroscopy uses many unique nuclear properties of specific isotopes. For example, Nuclear Magnetic Resonance (NMR) spectroscopy can be used only for isotopes with a nonzero nuclear spin. Isotopes commonly used for NMR spectroscopy are 11H, 21D, 157N, 136C, and 3115P.

Isobars

Term “isobars” for nuclides was suggested by Alfred Walter Stewart in 1918 and is derived from the Greek word isos, which means “equal” and baros, means “weight”

Isobars are atoms of different chemical elements having the same number of nucleons. Isobars has different atomic number but same mass number. Example of isobars are 3240S, 3440Cl, 1840Ar, 1940K, and 2040Ca. The nuclei of all these nuclides contain 40 nucleons but are varying in numbers of protons and neutrons.

So, Isobars are the atoms having same mass number but different atomic number. For example, the atomic number of carbon and nitrogen is 6 and 7 respectively.

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Example:

NEET Foundation Chemistry Structure Of Atom Example

Isotones

Isotones are the atoms that have the same neutron number but different number of proton. For example, 3616S, 3717Cl, 3818Ar, 3919K and 4020Ca are all isotones of 20 since they all contain 20 neutrons.

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