Water and Life

polar covalent bonds

a covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

polar molecule

a molecule (such as water) with an uneven distribution of charges in different regions of the molecule.

cohesion

the linking together of like molecules, often by hydrogen bonds.

adhesion

the clinging of one substance to another, such as water to plant cell walls by means hydrogen bonds.

surface tension

a measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules.

kinetic energy

the energy associated with the relative motion of objects. Moving matter can perform work by imparting motion to other matter.

heat

the total amount of kinetic energy due to random motion of atoms or molecules in a body of matter; also called thermal energy. Heat is energy in its most random form.

temperature

a measure of the intensity of heat in degrees, reflecting the average kinetic energy of molecules.

celsius scale

a temperature scare (C) equal to 5/9 (F-32) that measures the freezing point of water at 0C and the boiling point of water at 100C.

calorie (cal)

the amount of heat energy required to raise the temperature of 1 g of water by 1C; also the amount of heat energy that 1 g of water releases when it cools by 1C. The calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.

kilocalorie (kcal)

a thousand calories; the amount of heat energy required to raise the temperature of 1 kg of water by 1C.

joule (j)

a unit of energy: 1 J = 0.239 cal; 1 cal = 4.184 J.

specific heat

the amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1*C.

heat of vaporization

the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to a gaseous state.

evaporative cooling

the process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state.

solution

a liquid that is homogeneous mixture of two or more substances.

solvent

the dissolving agent of a solution. Water is the most versatile solvent known.

solute

a substance that is dissolved in a solution.

aqueous solution

a solution in which water is the solvent.

hydration shell

the sphere of water molecules around a dissolved ion.

hydrophilic

having an affinity for water.

colloid

a mixture made up of a liquid and particles that (because of their large size ) remain suspended rather than dissolved in that liquid.

hydrophobic

having no affinity for water; tending to coalesce and form droplets in water.

molecular mass

the sum of the masses of all the atoms in a molecule; sometimes called the molecular weight.

mole (mol)

the number of grams of a substance that equals its molecular weight in daltons and contains Avogadro's number of molecules.

molarity

a common measure of solute concentration, referring to the number of moles of solute per liter of solution.

hydrogen ion (H+)

a single proton with a charge of 1+. The dissociation of a water molecule (H2O) leads to the generation of a hydroxide ion (OH-) and a hydrogen ion (H+); in water, H+ is not found alone but associates with a water molecule to form a hydronium ion.

hydroxide ion (OH-)

a water molecule that has a lost a proton; OH-.

hydronium ion (H3O+)

a water molecule that has an extra proton bound to it; H3O+, commonly represented as H+.

acid

a substance that increases the hydrogen ion concentration of a solution.

base

a substance that reduces the hydrogen ion concentration of a solution.

pH

a measure of hydrogen ion concentration equal to -log [H+] and ranging in value from 0 to 14.

buffer

a solution that contains a weak acid and its corresponding base. A buffer minimizes changes in pH when acids or bases are added to the solution.

ocean acidification

decreasing pH of ocean waters due to absorption of excess atmospheric CO2 from the burning of fossil fuels.

acid precipitation

rain, snow, or fog that is more acidic than pH 5.2.