What's the difference between groups and periods in a periodic table?

On the periodic table, there are both groups and periods.

Periods go horizontal on the periodic table are there are 7 groups in all. Groups are very important because they tell you the number of electrons shells also called orbitals.

On the other hand, groups are the vertical columns on the period table. There are 18 groups and the elements in each group correspond to the number of valence electrons.

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