<span>There is a direct correlation between the period number and the energy level for valence electrons. For example, the H and He elements, in period 1, have their outer electrons in the energy level "1". This continues down the rows: all the elements in period 2 have their principal energy level as n = 2, period 3 has n = 3, and so on.</span>
Pyrophoricity is a property of metals and oxides of lower oxidation states, including radioactive ones, in which they spontaneously ignite during or after stabilization.
