Chemical elements of the first period

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The first period of the periodic table of the elements includes all chemical elements that have only one electron shell in the atom . This electron shell is also called the valence shell of the atom. Since this first electron shell can only hold a maximum of two electrons , there are only two chemical elements in the first period. The valence shell, which largely determines the properties of a chemical element, is already fully occupied with 2 electrons in elements of the 1st period. In all other periods the valence shell is only fully occupied from 8 electrons.

Extract from the periodic table

group 1 18th

Atomic number

other non-metals Noble gas

Common characteristics

Both chemical elements of the first period are gaseous under standard conditions , are colorless gases and have diamagnetic properties.

The gases

Magic number

The chemical element helium with atomic number two has a higher stability in the basic state of the atomic nucleus than neighboring nuclides . This particular ordinal number is known as the magic number .

Number of electrons in the electron shells

Electron shell Number of electrons comment
All in all s orbital p orbital d orbital f orbital
1 1 to 2 1 to 2 - - - outermost electron shell , valence shell


Atomic number symbol Surname Element category Physical state Electron configuration
1 H hydrogen other non-metals gaseous 1s 1
2 Hey helium Noble gases gaseous 1s 2