Water and Life (Chapter 3) – Key Terms

Polar molecule

A molecule with partial positive and partial negative regions due to polar covalent bonds (water is a polar molecule).

Hydrogen bond

A noncovalent attraction between a hydrogen atom on one molecule and a highly electronegative atom (such as oxygen) on another molecule.

Hydrogen bonding

The attraction between hydrogen atoms on one water molecule and electronegative atoms on neighboring molecules, forming a network.

Cohesion

Attraction among water molecules due to hydrogen bonding, causing water to stick together.

Surface tension

A measure of how difficult it is to stretch or break the surface of a liquid, driven by cohesive forces.

Adhesion

The clinging of water to other substances, such as cell walls, through hydrogen bonding.

Temperature regulation (water)

Water moderates air temperature by absorbing heat from warm air and releasing heat to cooler air.

Kinetic energy

The energy of motion of particles.

Thermal energy

Total kinetic energy of all molecules in a substance; depends on volume.

Temperature

Average kinetic energy of the molecules in a body of matter.

Calorie (cal)

The amount of heat required to raise 1 g of water by 1°C.

Kilocalorie (kcal)

1000 calories; commonly used unit of food energy.

Joule (J)

A unit of energy; 1 J = 0.239 cal.

Specific heat

The amount of heat needed to raise the temperature of 1 g of a substance by 1°C; for water it is 1 cal/(g·°C).

Heat of vaporization

The amount of heat required to convert 1 g of a liquid to a gas.

Evaporative cooling

As liquid molecules with high kinetic energy leave as vapor, the remaining liquid cools.

Vaporization

The process of a liquid becoming a gas.

Solution

A homogeneous mixture of two or more substances.

Solvent

The dissolving agent in a solution; water is a common solvent.

Solute

The substance dissolved in the solvent.

Aqueous solution

A solution in which water is the solvent.

Hydration shell

The sphere of water molecules surrounding a dissolved ion.

Hydrophilic

Having an affinity for water; typically ionic or polar substances.

Hydrophobic

Repelling or failing to mix with water; typically nonpolar substances.

Mole (mol)

A unit equal to 6.02×10^23 particles (Avogadro’s number).

Avogadro's number

6.02×10^23; the number of objects in one mole.

Molarity (M)

Moles of solute per liter of solution.

Hydrogen ion (H+)

A free proton; represents acidity in solution.

Hydroxide ion (OH−)

A negatively charged hydroxide ion; represents basicity in solution.

Hydronium ion (H3O+)

Water molecule that has gained a proton (H+) in solution.

Acid

A substance that increases the H+ concentration in a solution.

Base

A substance that reduces the H+ concentration (or increases OH−) in a solution.

pH

A measure of H+ concentration; pH = -log[H+], on a scale from 0 to 14.

Buffer

A substance that minimizes changes in pH by accepting or donating H+.

Ocean acidification

CO2 dissolving in seawater forms carbonic acid, lowering ocean pH and affecting calcification.