AP Biology 1.1 | STRUCTURE OF WATER AND HYDROGEN BONDING

Bond strength order from strongest to weakest

Covalent bonds are strongest, then ionic bonds, then hydrogen bonds which are the weakest and easiest to break

Covalent bond

A bond where electrons are shared between two atoms

Nonpolar covalent bond

A covalent bond with equal sharing of electrons

Polar covalent bond

A covalent bond with unequal sharing of electrons

Ionic bond

A bond where electrons are transferred from one atom to another

Hydrogen bond

A weak attraction, not a true physical bond, between an electronegative atom and a hydrogen atom

Which atoms does hydrogen bond to

Nitrogen, oxygen, or fluorine, since these are electronegative

How hydrogen bonds are drawn compared to covalent bonds

Hydrogen bonds are drawn with dotted lines to show weakness, covalent bonds are drawn with solid lines

Why water is a polar molecule

Oxygen pulls electrons more strongly, giving oxygen a partial negative charge and the hydrogens a partial positive charge

Universal solvent

A description of water, since like dissolves like and water can dissolve many polar and ionic substances

Hydrophilic

A term for water loving molecules that can form hydrogen bonds, are polar, and are soluble

Hydrophobic

A term for water fearing molecules that are nonpolar and insoluble

Why water has high specific heat

A lot of energy is needed to break the many hydrogen bonds between water molecules, so water resists temperature change and helps organisms maintain internal temperature homeostasis

Why water has a high heat of vaporization

A lot of energy is needed for water to go from liquid to gas, which leads to evaporative cooling such as sweat cooling the skin

Why water has high surface tension

Hydrogen bonds make it difficult to break the surface of water

Cohesion

The attraction of water molecules to other water molecules

Adhesion

Water clinging to other surfaces or substances

Capillary action

Upward movement of water through a narrow tube caused by adhesion and cohesion, important for transpiration in plants

Why ice floats on water

As water freezes the hydrogen bonds form a crystal lattice that spaces the molecules farther apart, making ice less dense than liquid water