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Periods in the Periodic TableThe horizontal rows of elements on the Periodic Table are called Periods. The period numbers give information about the number of electron shells in the atoms. In the elements of Period 2, the atoms have two electron shells. In Period 3 they have three. (But the shell structure gets more complex from Period 4 onwards.)
Metal versus Non-MetalOver three-quarters of the elements are metals. Only two groups, the halogens and the noble gases, are completely non-metal.
HydrogenHydrogen has one outer electron like the Group 1 metals. However, hydrogen is a gas and usually reacts like a non-metal.
Trends in the Periodic TableThe elements in each numbered group show trends in their properties. For example, as you go down Group 1, the elements become more reactive. As you go down Group 7, they become less reactive.
VideosGroups of the Periodic Table Groups of the Periodic Table
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