Water Living organisms depend on the unique properties of water.

H 2 O Molecule 2 atoms of hydrogen: Atomic # = 1 How many protons and electrons? 1 atom of oxygen: Atomic # = 8 How many protons and electrons? 2 atoms of hydrogen: Atomic # = 1 How many protons and electrons? 1 atom of oxygen: Atomic # = 8 How many protons and electrons?

Electron Configuration of Water

Space-Fill Model of Water

Water Molecule Polarity Oxygen is a bigger atom with 8 protons and pulls more forcefully on the electrons than hydrogen does. This creates positive (+) and negative (-) poles on the molecule. Oxygen is a bigger atom with 8 protons and pulls more forcefully on the electrons than hydrogen does. This creates positive (+) and negative (-) poles on the molecule.

Polar Covalent Bonds Bonds that form when electrons are shared unevenly. Areas of the molecule are slightly charged, although water molecules remain neutral. Bonds that form when electrons are shared unevenly. Areas of the molecule are slightly charged, although water molecules remain neutral.

Hydrogen Bonds Hydrogen (+) of one molecule is attracted to a nearby atom (-) of a different molecule of water or other substance

Hydrogen Bonds are Weak Electrons are not shared, gained, or lost Temporary bonds form Bonds are easily broken

Hydrogen Bonds form in Water and DNA

Cohesion

Adhesion

Surface Tension

Special Properties of Water Cohesion: Attraction of same molecules to each other Adhesion: Attraction of different molecules to each other Surface Tension: The force needed to break the surface of a liquid due to cohesion Cohesion: Attraction of same molecules to each other Adhesion: Attraction of different molecules to each other Surface Tension: The force needed to break the surface of a liquid due to cohesion

Polar and Non-Polar Molecules

Polar molecules repel non-polar molecules Water is polar Oil is non- polar

The Cell Membrane has Polar and Non-Polar Regions

Capillary Action: How Water Moves up Plants Plant tubes (xylem) are made of cellulose which is polar. Water molecules are attracted to the sides of thin tubes of xylem.

Soap and Water The surface of water has high tension due to the strong force of cohesion. Soap molecules have two ends. One end is attracted to water and the other end repels water. Soap separates the water molecules and breaks the surface tension. The surface of water has high tension due to the strong force of cohesion. Soap molecules have two ends. One end is attracted to water and the other end repels water. Soap separates the water molecules and breaks the surface tension.

What Happened to the Pepper? Pepper floats on the water. Soap break the surface tension of water by getting “between” water molecules. Pepper scatters as water’s hydrogen bonds are broken near the soap. Pepper floats on the water. Soap break the surface tension of water by getting “between” water molecules. Pepper scatters as water’s hydrogen bonds are broken near the soap.

How many drops of water can you place on a penny?

 ology/Biology1111/animations/hydroge nbonds.html ology/Biology1111/animations/hydroge nbonds.html  ology/Biology1111/animations/hydroge nbonds.html ology/Biology1111/animations/hydroge nbonds.html