In this video we’ll use the Periodic table and a few simple rules to find the protons, electrons, and neutrons for the element Helium (He). From the Periodic Table we can find the element symbol, atomic number, and atomic mass. Using this information we can find the other information.
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Atomic Number = Number of Protons
Number of Protons = Number of Electrons (for a neutral element)
Mass Number = Number of Protons + Neutrons
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The Atomic Mass is usually written below the number. If you are confused the Atomic Mass will be the larger number – think of it as more massive than the Atomic Number. Often it also has decimals.
If you are not given the Mass Number, it’s best to round to the Atomic Mass to the nearest whole number. For example, with He we have 4.00. We can round this to 4.
