In this video we’ll use the Periodic table and a few simple rules to find the number of protons and electrons for the Hydrogen cation (H+). From the Periodic Table we can find the element symbol, atomic number, and atomic mass. Using this information we can find the other information for H+.

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Atomic Number = Number of Protons

Number of Protons = Number of Electrons (for a neutral element)

***For ions the only difference is in the electron.***

When at atom loses electrons a positive ion is formed. For example, with Ca 2+, the 2+ tells you that two electrons were lost.

When at atom gains electrons a negative ion is formed. For example, with N 3-, the 3- tells you that three electrons were gained.

With something like Na+ or Cl-. we assume that we have 1+ and 1- even though the number "1" is not written.

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Information on the Number of Neutrons and Mass

Mass Number = Number of Protons + Neutrons

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 Carbon (C) we have 12.01. We can round this to 12.

Note, that sometimes, for example, you are given a Mass Number of 1 for Hydrogen. This can happen because Hydrogen atoms usually have 0 neutrons. But sometimes a H atom will 1 or 2. These are the three different isotopes for H. They have the same number of protons but different numbers of neutrons and therefore a different Mass Number.

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