# Non-polar hydocarbons in phospholipid bilayer

I read that the phospholipids in many cell membranes (I am referencing neurons specifically) have a non-polar hydrocarbon tail and a polar phosphate head. Regarding the non-polarity of the hydrocarbon - are all hydrocarbons non-polar (I think I understand that this is calculated by seeing if there is a non-zero dipole moment for the molecule)? Why are the phospholipid tails attracted to each other enough to form a seal that overcomes large concentration gradients?