AP Biology: Polar vs. Nonpolar Review

A set of flashcards covering polar vs. nonpolar molecular properties, chemical bonds, phospholipid behaviors, and cellular membrane interactions for AP Biology.

Polar molecule

A molecule where electrons are shared unequally, creating partial positive and negative regions.

Nonpolar molecule

A molecule where electrons are shared more equally, so it does not have strong partial charges.

Why is water polar?

Oxygen attracts the shared electrons more strongly than hydrogen, making O slightly negative and H slightly positive.

Partial charge

A small charge caused by unequal sharing of electrons; written as delta positive or delta negative.

Hydrophilic

Water-loving. Polar or charged substances that interact well with water.

Hydrophobic

Water-fearing. Nonpolar substances that do not mix well with water.

Like dissolves like

Polar substances tend to dissolve in polar substances; nonpolar substances tend to dissolve in nonpolar substances.

Why does oil separate from water?

Water is polar and oil is nonpolar, so they do not interact favorably and separate.

O-H bond

Usually polar because oxygen pulls electrons more strongly than hydrogen.

N-H bond

Usually polar because nitrogen pulls electrons more strongly than hydrogen.

C-H bond

Usually treated as nonpolar in AP Biology because carbon and hydrogen share electrons fairly evenly.

How can you spot a polar molecule?

Look for electronegative atoms such as oxygen or nitrogen and an uneven distribution of charge.

How can you spot a nonpolar molecule?

Look for lots of carbon-hydrogen bonds and few strongly electronegative atoms.

Phospholipid head

Polar and hydrophilic; it interacts with water.

Phospholipid tails

Nonpolar and hydrophobic; they avoid water.

Why do phospholipids form bilayers?

Their hydrophilic heads face water while their hydrophobic tails cluster away from water.

Polar vs. nonpolar in membranes

Small nonpolar molecules cross the lipid bilayer more easily than charged or strongly polar molecules.

Main AP Bio connection

Polarity affects solubility, membrane structure, protein interactions, and how molecules behave in cells.

Fast memory rule

Polar = has partial charges and mixes with water. Nonpolar = no strong partial charges and avoids water.