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Period 1 element

A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the elements.

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Period one is much shorter than any other row in the table, and contains only two elements, hydrogen and helium. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements do not obey the "octet rule".

These are:

**Chemical elements in the first period**
Group	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
# Name	1 H																	2 He
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Element categories in the periodic table

Metals						Metalloids	Nonmetals
Alkali metals	Alkaline earth metals	Inner transition elements		Transition elements	Other metals		Other nonmetals	Halogens	Noble gases
		Lanthanides	Actinides