The characteristics of water that make it important to living things. Chemistry of Water The characteristics of water that make it important to living things.

Water FACTS Water is the most abundant compound on Earth's surface, constituting about 70% of the planet's surface. In nature it exists in the liquid, solid, and gaseous states. Water is the only common substance found naturally in all three common states of matter and it is essential for life on Earth. Many substances dissolve in water and it is commonly referred to as the universal solvent. Because of this, water in nature and in use is rarely pure and some of its properties may vary slightly from those of the pure substance. There are many compounds that are essentially, if not completely, insoluble in water. Water usually makes up 55% to 78% of the human body, averaging 70%.

Properties and other things to know about Water: 1.     Chemical Formula  2.  Bond  3. Storage of Energy 4. Attraction 5. Effect on Human Body 6. Aqueous solution 7. Polarity 8. Acids and Bases

Chemical Formula H2O Two hydrogen atoms and one oxygen atom bonded together.

Molecule is formed by covalent bonds Molecule is formed by covalent bonds. The electrons in a water molecule are shared by oxygen and hydrogen atoms. HOWEVER… The shared electrons are attracted more strongly by the oxygen nucleus than by the hydrogen nuclei. (The oxygen nucleus has more protons [+] to be attracted to.) This makes the oxygen more negative because 10 electrons are staying close around its nuclei of 8 protons. Bond

Storage of Energy Water absorbs heat more slowly and retains this energy longer than other substances. Ex: Humans sweat to release excess heat through water evaporation. Water vapor lost through the evaporation of sweat carries heat away from the body. Helps with Homeostasis!

Storing Energy                 

Attraction The hydrogen bonds between water molecules cause the cohesion of liquid water. COHESION is an attraction between substances of the SAME kind. Because of cohesion water droplets form thin films and drops, creating SURFACE TENSION. Water molecules are also attracted to many other polar substances. ADHESION is an attraction between different substances, creating CAPILLARY ACTION in plants which moves water from roots to leaves. Adhesion can also cause stuff to be wet, like a paper towel.

Surface Tension (Cohesion)

Capillary Action (Adhesion)

NO Adhesion? Water would be like this if the molecules did not stick together.

Effects on Human Body 70% of your body is made of water. 2/3 of molecules in your body are water. Your cells are filled with water. Water is where most cell events occur. Cells are surrounded by water. Water helps move nutrients and waste in and out of your cells.

Aqueous solutions Many substances dissolve in water Example: Salt dissolves in water, making a saltwater solution. Many substances in the body are dissolved in blood or other aqueous fluids. Water allows substances to move in and out of cells. Like sugars!

Aqueous solution

polarity Water molecules have a partially positive end and a partially negative end or poles. Partially positive end of one water molecule is attracted to the partially negative end of another water molecule. Attraction between 2 water molecules is called a HYDROGEN BOND. It is a weak bond between 2 polar molecules.

Attraction between two water molecules: Notice the polarity!

Acids and bases While bonds in water molecules are strong, at any given time, a small fraction of those bonds might break, forming a hydrogen ion H+ or a hydroxide ion OH- . Pure water has a low concentration of hydrogen ions and hydroxide ions present in equal numbers.

Acids and Bases

ACIDS Compounds that form hydrogen ions when dissolved in water are called acids. When an Acid is added to water, the concentration of hydrogen ions in the solution is increased above that of pure water.

Bases Compounds that reduce the concentration of hydrogen ions in the solution are called bases. Many bases form hydroxide ions when dissolved in water. This lowers the concentration of hydrogen ions because hydroxide ions react with hydrogen ions to form water molecules.