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How to Use the Periodic Table of Elements to Count Electrons & Protons

If you were given a list of 10 people and asked to rank them, you might rank them according to height (shortest to tallest), age (youngest to oldest) or wealth (poorest to richest). A periodic table of the elements ranks elements not by inches, years or dollars but by the number of protons in the nucleus of an atom of each element. Arranged in this way, the elements display repeating --- or periodic --- patterns of behavior and characteristics. The nonreactive gases helium, neon, argon, krypton, xenon and radon, for example, cluster in the last column on the right-hand side of the periodic table while the highly reactive metals lithium, sodium, potassium, rubidium, cesium and francium cluster in the first column on the left-hand side of the table.

Things You'll Need

  • Textbook or online reference of element names and abbreviations
  • Periodic table of the elements
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Instructions

    • 1

      Choose an element to analyze. For example, you may decide to analyze lithium.

    • 2

      Consult a textbook or online listing of the elements and their scientific abbreviations. For example, you can access the National Center for Biotechnology Information website PubChem Compound.

    • 3

      Find or enter the name of the element you want to analyze and discover its scientific abbreviation, or molecular formula (MF). For example, you enter the word "lithium" on the PubChem Compound site and learn that the molecular formula of lithium is Li.

    • 4

      Access a textbook or online periodic table of the elements and find the molecular formula you have identified. For example, you can access the Queen Mary University of London periodic table. You identify the molecular formula Li in the first column of the table, second row from the top.

    • 5

      Read the number in the top left-hand corner or top center of the box designated by the molecular formula you have identified. For example, you read the number 3 at the top center of the box designated Li on the Queen Mary University of London periodic table. This number is the atomic number of lithium.

    • 6

      Note that the atomic number of an element is the number of protons in the nucleus of an atom of that element. For example, there are three protons in the nucleus of an atom of lithium.

    • 7

      Note also that each atom of each element has exactly as many electrons as it has protons. If an atom has seven protons, it will have seven electrons. For example, the atom of lithium you are analyzing has three protons. This atom of lithium must also have three electrons.


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