What is an ion? You know that the atomic number of an element represents the number of protons it has. And that on the periodic table represents a neutral charge. But when an atom gains or looses electrons, it becomes positive or negative.
Types: When the net electrical charge of the ion is positive, it is said to be a cation and when it is negative it is said to be an anion.
How to represent them: on the picture to the left we have a lithium atom. It´s neutral right now and has 1 valence electron, but what happens if we remove that electron? We would get an ion as shown on the right and it would be called a Li+1 showing it has one more postitive molecule.
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Ions