Let's begin by drawing a sigma oracovalent bond between oxygen and nitrogen. So once we draw this line, that basically means that one electron is being donated by H and one electron is being donated by o. Now, this means that all the orbitals, meaning this one s orbital, is completely filled for H. Because before, when H is by itself, it has one electron in its one s shell. But now this electron is being shared. So we have two electrons in the one s shell. And that means all electrons or all the orbitals of the age are completely filled.