increases down the group in the periodic table, or that hydrogen's reactivity is evidenced by its reaction with oxygen.
Hydrogen does not react with oxygen—even though the equilibrium constant is very large—unless a flame initiates the radical reaction, which leads to an explosion.
For instance, grinding a sample to a higher specific surface area increases its reactivity.
For example, the statement that "sodium metal is reactive" suggests that sodium reacts with many common reagents (including pure oxygen, chlorine, hydrochloric acid, and water), either at room temperature or when using a Bunsen burner.
Generally, electrons exist in orbitals that are the result of solving the Schrödinger equation for specific situations.
However, the activation energy to go from half-filled to fully-filled p orbitals is negligible, and as such, carbon forms them almost instantaneously.
One approach to generalize the above is the activation strain model[1][2][3] of chemical reactivity which provides a causal relationship between, the reactants' rigidity and their electronic structure, and the height of the reaction barrier.