CIE AS Level Chemistry 9701:Topic 1: Atomic structure – Unit : 1.2 Isotopes Study Notes

Isotopes: Basics

  • Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
  • The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number
    • Eg. carbon-12 and carbon-14 are isotopes of carbon containing 6 and 8 neutrons
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The atomic structure and symbols of the three isotopes of hydrogen

Isotopes: Chemical & Physical Properties

  •  Isotopes have similar chemical properties but different physical properties

Chemical properties

  • Isotopes of the same element display the same chemical characteristics
  • This is because they have the same number of electrons in their outer shells
  • Electrons take part in chemical reactions and therefore determine the chemistry of an atom

Physical properties

  •  The only difference between isotopes is the number of neutrons
  • Since these are neutral subatomic particles, they only add mass to the atom
  • As a result of this, isotopes have different physical properties such as small differences in their mass and density
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