And two, they cannot form those same stabilized interactions with the hydrocarbon tails found inside the core of that bilateral membrane. So we see that ions such as sodium ions, potassium ions or chloride ions have a very low permeability. They cannot pass across that cell membrane as shown in the following diagram. So we have a potassium ion, let's say, found on the outside of that cell membrane. And this is the phospholipid bilayer. And notice that it exists in this cage, in this salvation shell, in which we have all these hydrogen bonds shown in green.