Period 1 of the Periodic Table
Period 1 of the periodic table has 2 elements, from Hydrogen (H) to Helium (He). The period number usually equals the number of electron shells of the atom, and in this period the 1s subshells are filled. Moving left to right across a period, the atomic number increases and the atomic radius usually decreases.
Element list
Frequently asked questions
How many elements are in period 1 of the periodic table?
Period 1 of the periodic table has 2 elements.
Which elements are in period 1?
The elements of period 1 run from Hydrogen to Helium: Hydrogen (H) and Helium (He).