How to Find Electrons for an Isotope


If your teacher asks you to find the number of electrons for an element on a quiz, it's your lucky day, because this is one question that just couldn't be simpler. If an atom hasn't lost or gained any electrons (if it hasn't been ionized, in other words), it will have the same number of electrons as there are protons in its nucleus, and that's regardless of the number of neutrons. Consequently, all isotopes of an element have the same number of electrons. Here's how to count them.

Things You'll Need

  • Pencil
  • Paper
  • Periodic Table
  • Find your element on the periodic table. If the element is mercury, for example, you'll find it under group (column) 12 in row (period) 6.

  • Find the atomic number of your element. The atomic number is listed directly above the symbol for the element and just below its name (if the name is listed). In the case of mercury, for example, the atomic number is 80. The atomic number will always be an integer.

  • Remember that the atomic number gives you the number of protons for that element. The number of electrons is the same as the number of protons. Consequently, mercury has 80 protons and 80 electrons.

Tips & Warnings

  • As you progress further in chemistry, you'll be able to locate elements without having to spend so much time searching.


  • Photo Credit BananaStock/BananaStock/Getty Images
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