Will usually have an acid, amine, amide, or alcohol functional group as their R-group.
Some may be more polar than others; for example, Aspartic acid is more polar than Serine as an acid functional group is more polar than one that is alcoholic.
Tend to be hydrophilic, and thus face towards the outside of protein structures.
Their R-groups will be pure hydrocarbon alkyl groups (alkane branches) or aromatic (benzene rings; the exception to this is the aromatic amino acid Tyrosine, which is polar).
Some may be more non-polar than others; this is based on the number of alkyl groups. For example, this makes valine more non-polar than alanine.
Tend to be hydrophobic, and thus face towards the inside of protein structures.