Horizontal rows = Periods
Vertical rows = Groups
*Number of electrons in the outer shell of the element determines the group it is in. [e.g. Na (sodium) has 11 electrons in the ratio 2:8:1. It has 1 electron in the outer shell so it is in Group 1.]
Group 1 metals are called alkali metals.
Group 2 metals are called alkali earth metals.
Group 7 elements are called halogens.
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