So let's begin by focusing on these four right over here. So notice that what these four have in common is each one of these side chain groups, which are shown in the colored region, are basically hydrocarbon molecules. And hydrocarbon molecules contain carbonate atoms, and they're non polar. And that makes them hydrophobic and non reactive. Now, as we go from left to right, the hydrocarbon group increases inside. So we essentially add two carbon atoms here.