The soap molecule has two parts: a polar group (-COO-Na+) and a non-polar group (R-hydrocarbon part). The polar group is called the head and the non-polar group is called the tail. Thus, the soap molecule has a polar head and a non-polar hydrocarbon tail. The polar head is hydrophilic in nature (water loving) and the non-polar tail is hydrophobic (water repelling) in nature.