The three isotopes of hydrogen. Image credit wikipedia.org

The three isotopes of hydrogen. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes: Isotopes and the importance of proton numbers

  • The electron orbits of these two elements is small and can only carry two electrons
  • The next element in the series is lithium
  • It comes with two electronic shells
  • The second outer shell can hold 8 electrons
  • Lithium has a proton number of three and has one electron in the outer shell
  • The way in which the electrons are arranged determines the reactions of the elements
  • The movement of electrons from one atom to another gives elements their chemical properties
  • Atoms of the same element are the same
  • They behave in the same way in a chemical reaction
  • Electrons can only escape from their orbits if energy is supplied
  • If they can do so easily then the element is very reactive

The nucleon number and isotopes

  • The proton number of an element does not include the number of neutrons in an atom
  • Because neutrons have no charge, an excess of them does not affect the charge of a nucleus
  • Some atoms have the same number of protons and electrons but a different number of neutrons
  • These atoms are known as isotopes
  • Isotopes have the same number of protons but a different number of neutrons
  • For example Chlorine 35 has 17 protons and 18 neutrons
  • and Chlorine 37 has 17 protons and 20 neutrons
  • These two are isotopes

To access more topics go to the Combined Science Notes page.

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