The two elements that only need valence electrons to be "happy" (i.e., to have a full outer shell and be stable) are hydrogen (H) and helium (He).

Here's why:

* Hydrogen (H) has only one proton and one electron. It needs one more electron to fill its first (and only) energy level, making it chemically similar to the noble gas helium.

* Helium (He) has two protons and two electrons. Its first energy level is full, making it stable and unreactive.

Therefore, both hydrogen and helium achieve stability by gaining or losing electrons to achieve a full outer shell.