Water and Its Importance

Water and Living Organisms

• Water is the most important compound in living organisms.

• It makes up 70 – 95% of most organisms.– Dissolves substances– Is a component of body solutions, such as

sweat, blood, tears, saliva, and urine– Carries substances throughout the body

The Chemistry of Water

• H2O• The compound itself

is held together by COVALENT bonds–Electrons move between the

2 Hs and 1 O–They are shared unequally–This causes POLARITY

Polarity of Water

• Polar molecule = molecule with an unequal distribution of charge– Positive at one end, negative at the other

• Nonpolar molecule = uncharged molecule

δ +

δ-

δ +

Polarity of Water

• Polarity is important because of how it allows the molecule to interact with other compounds–It can dissolve many ionic compounds–Allows for hydrogen bonding

Polarity of Water

Dissolving Compounds

• Water can easily dissolve ionic compounds, such as salt (NaCl).

Dissolving Compounds

Hydrogen Bonding

• Water molecules hydrogen bond to each other

• Cohesion: Ability to stick to each other• Adhesion: Ability to stick to other

molecules• Hydrogen bonding is also

important in DNA and proteins

Hydrogen Bonding

H-bonding and Density

• In ice, more hydrogen bonds cause the molecules to spread out = less dense

H-bonding & Density

H-bonding and Specific Heat

• Specific Heat = the amount of energy needed to increase the temperature of 1g of a substance by 1°C

• When you go to the beach in the summer, which is hotter, the sand or the ocean?

• Water has a high specific heat– It takes more energy (heat) to increase the

temperature of water than many other substances

Specific Heat of Water

All of these properties make water an extremely important molecule

to all living things!