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Answer:

Explanation:

There are seven periods in the periodic table, with each one beginning at the far left. A new period begins when a new principal energy level begins filling with electrons. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. Periods 4 and 5 have 18 elements.

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Answer:

18 groups

In the periodic table, there are 7 periods and 18 groups.

Explanation:

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