Ch.3 Water and Life

Polar covalent bonds form when there is an

uneven distribution of shared
electrons, with them being attracted to one atom more than another

Hydrogen bonds are weak chemical bonds formed when a

partially positive
hydrogen atom of a polar molecule is attracted to a partially negative atom

Water can naturally exist in

any one of three phases of matter, each of which are differentiated by density and hydrogen bond structure

The state that water exists in is governed by the amount of

energy the
molecules have

In liquid water most of the molecules are held together by

hydrogen bonds into small groups, but because the bonds are weak the groups can break up and reformas the fluid moves

In water vapor the molecules have more energy are not held together by

hydrogen
bonds and move much faster and more freely than in liquid water

In ice a regular pattern of

hydrogen bonds fix the low-energy molecules in a
crystalline structure

Kinetic energy is the energy of

motion

Thermal energy is the total energy of a substance due to

the kinetic energy of the random motion of atoms and molecules as well as chemical energy due to molecular structure

Temperature represents the

average kinetic energy of the molecules and particles of a body of matter regardless of the total volume of that matter (decouples energy from volume and mass)

Heat energy is a form of energy transfer that is not used for work and flows

“downhill” from a system with higher energy to a system with lower energy

The speed at which atoms and molecules move affects their ability to

form bonds with each other

The latent heat of melting (and fusion) is the amount of energy required to change

1g of a substance from a solid to a liquid and vice versa

The latent heat of vaporization (and condensation) is the amount of energy required to change

1g of a substance from a liquid to a gas and vice-versa

Water vapor: molecules leave liquid water and evaporate into water vapor as
temperatures increase, and the point of complete evaporation for a body of water
occurs at

100°C

As water cools, the molecules move slower and the fluid also becomes more dense, with liquid water being densest at

4°C

Ice: eventually low-density cold-water freezes and crystalizes into ice at

0°C with regularly spaced hydrogen bonds

As heat is applied to frozen water, the heat energy works to

break hydrogen bonds
but does not significantly increase the speed of the molecules

The crystalline lattice structure formed by

the regularly spaced hydrogen bonds in ice reduces its overall density

The ability of ice to float on water is extremely important for

the overall survivability of all life on Earth (either directly or indirectly)

Specific heat is the amount of

heat energy that needs to be gained or lost by a substance for 1g of that substance to change its temperature by 1°C

The heat capacity is the amount of

heat that must be added to a substance to raise its temperature by a given amount, but this capacity also reflects that substance's ability to store heat

Because of water’s high specific heat, a body of water can

gain or lose a large amount of energy without significantly changing its temperature

Evaporation in water occurs when

molecules move fast enough to escape from the hydrogen bonds present in a liquid to a vapor (gaseous) state

Evaporative cooling occurs when the surface of a substance (or organism) becomes cooler as a result of

evaporation in which molecules with the greatest amount of thermal energy escape to water vapor

Cohesion is the attraction between

molecules of the same type and their increased likelihood to “stick together”

Surface tension is the measure of how difficult it is to

stretch or break the surface of a liquid

Adhesion is the attraction of

one substance to another

Adhesion allows water to move upward against gravity in a process called

capillary action,
which is essential to the survival of plants

The combination of cohesion and adhesion of water molecules allows plants to

draw water and dissolved nutrients into their tissues against gravity

A solution is a liquid containing a

homogenous (evenly distributed) mixture of two or more substances (compounds)

The solvent is the

liquid or dissolving agent

The solute is the

substance that is dissolved

An aqueous solution is a

solution in which the solvent is water

The ions eventually attract enough water molecules to cause an “insulating” layer of water (called a

hydration shell) to form around eachion, which dissociates the ions from each other and dissolves the salt

The chemical formula of water is H 2O and it is referred to as the

solvent of life

Because of the polarity of water, it can easily dissolve other polar molecules but
cannot dissolve

nonpolar molecules

Hydrophilic substances can

dissolve or “move” through water

Hydrophobic substances

cannot dissolve in water

Though rare, hydrogen atoms of one water molecule will transfer to another water molecule in a process called

dissociation

Hydrogen ion (H+)

a single proton will transfer to the other water molecule while leaving its electron behind

Hydroxide ion (OH- )

results from the water molecule that lost a proton but still retains the original electron configuration

Hydronium ion (H3O+)

results from the water molecule that gains a proton but still retains the original electron configuration

An acid is a substance that

increases the hydrogen ion concentration in a solution

A base is a substance that

reduces the hydrogen ion concentration in a solution

A buffer is a substance that

minimizes changes in pH by accepting H + ions when they are too abundance and releasing H + ions when they are depleted

The pH (scale) is the measurement of the

relative H+ (hydrogen ion)concentration in a solution

The pH ranges from

0 (most acidic) to 14 (most basic) with a pH of 7 being neutral

Acidic solutions are those that have higher concentrations of

H + than OH -

Basic solutions are those that have higher concentrations of

OH - than H +

Neutral solutions are those that have equal concentrations of

Both H+, and OH-

“True” neutral solutions like pure water have a pH of

7

Most biological solutions (except biologically necessary acids) have a pH ranging
from

6 – 8

Ocean acidification is the process in which the pH of the ocean is

decreased (making the water more acidic) as a result of increased atmospheric and oceanic carbon dioxide (CO2) concentrations

As pH drops,

free hydrogen ions combine with carbonate ions (CO 32- ) to form bicarbonate ions (HCO3- )

Organisms like hermatypic corals (the ones that build reefs), mollusks, and arthropods rely on

calcium carbonate (CaCO 3) and carbonate ions in order to build shells and skeletons