Learning Target: Properties of Water

Ch. 2.2 (pp. 40 – 43)

Learning Target: Properties of Water

I Can… Describe the unique properties of water that allow life to exist on Earth.

I Will…• Describe the structure of a water molecule and explain

why a water molecule displays polarity.• Explain how hydrogen bonds allow for water molecules

to display properties of cohesion and adhesion.• Explain why water is considered a universal solvent.• Discuss how water’s properties relate to the

characteristics of life.

Learning Target: Properties of Water

Water is a Polar Molecule:• Unequal sharing of electrons

creates the appearance of charged areas on a water molecule.

• Greater electron concentration occurs in oxygen’s valance shell giving the appearance of a negative charge.

• Lack of electrons on the hydrogen side yields an appearance of a slightly positive charge

Learning Target: Properties of Water

Water is a Polar Molecule:• The partial negative δ-

and partial positive δ+ charges on water molecules allow them to form weak bonds called Hydrogen bonds.

• This allows water molecules to form an organized pattern of bonding.

Learning Target: Properties of Water

Water is a Polar Molecule:• Water is unique in that it is less dense in its solid state

than in its liquid state.• As the energy level in the water decreases the length

of the hydrogen bonds increase.

Learning Target: Properties of Water

Water is a Polar Molecule:• Hydrogen bonds are 20x weaker than covalent bonds,

but are strong among water molecules.• Requires a large amount of energy to overcome the

attractive force between water molecules.• Three important properties result:• High specific heat• Cohesion• Adhesion

Learning Target: Properties of Water

Water is a Polar Molecule:• High Specific Heat – resistance to change in temperature• Water must absorb a very large amount of heat energy

in order to increase in temperature.• This is very important for cells, that are mostly water.• Metabolic chemical reactions give off a lot of heat

energy and the water in cells absorbs the heat and regulates the cell’s temperature.

• Important for aquatic life forms.• Weather and climate.

Learning Target: Properties of Water

Water is a Polar Molecule:• Cohesion – the attraction of

one water molecule to another.• Gives rise to surface

tension of water. • Adhesion – The attraction

between a water molecule and a different substance.• Gives rise to capillary

action. A > C C > A

Learning Target: Properties of Water

Water is a Solvent:• Water is necessary as a matrix for chemical reactions

to take place in.• Water is necessary for transport of materials (both

inside the cell – intracellular and outside the cell – extracellular).• Solution – homogeneous mixture• Solvent – substance in greater amount which

takes in another substance(s).• Solute(s) – substance in lesser amount which

enters into another substance.• Concentration – ratio of solute in solvent

Learning Target: Properties of Water

Water is a Solvent:• Polar molecules will dissolve into water.• Attractive force of water cohesion is less than the

adhesion attraction of the water molecules to other polar molecules.

Nonpolar molecules will not dissolve in water.• Fats/Oils

Learning Target: Properties of Water

Water is a Solvent:• Ionic compounds deionize

in water.• Ionic charges are

attracted to the water molecules partial charges.

• Water surrounds ions and pulls them apart

Learning Target: Properties of Water

Water is a Solvent:• Water is the matrix for acid and base solutions.• Acids are compounds that increase the Hydrogen ion

concentration [H+] in solution.• Bases are compounds that reduce the [H+]

concentration (often by releasing hydroxyl ions [OH-]) in solution.

• pH is an important factor in organisms because many enzymes that are necessary for metabolic reactions to take place are damaged by changes in pH.

• Many organisms regulate pH levels with buffers.• Buffers either bind to excess [H+] ions or release them.

Learning Target: Properties of Water

Learning Check √:

1. Explain how the properties of water relate to the characteristics of life and allow for life to exist on Earth.