Period 1 element

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

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
e--conf.

Element categories in the periodic table

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

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