Chapter 4 Section 4 Unique Properties of Water

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Transcript Chapter 4 Section 4 Unique Properties of Water

Chapter 4 Section 4 Unique Properties of Water

Mrs. Kerstetter Biology

Structure of Water

    All living things are dependent on water Cells are surrounded by fluid that is mostly water Cells are 70-95% water Formula for water?

  H 2 O H atoms are joined to O atoms by a

covalent

bond

single

Key to water’s unusual properties:

1.

2.

3.

Electrons of each covalent bond are not shared equally between the H & O atoms Oxygen has a stronger attraction The unequal sharing causes the Oxygen to have a slightly negative (-) charge, while the hydrogen ends have a slightly positive (+) charge

Polarity

 A molecule in which opposite ends have opposite electrical charges is called a POLAR molecule  Water is a polar molecule

How are water molecules attracted to each other?

 Slightly negative O attracts the slightly positive hydrogen of adjacent molecules, causing molecules to become arranged using hydrogen

bonds

Water’s Unique Properties

1.

2.

3.

4.

Cohesion and Adhesion Temperature Moderation Low Density of Ice Ability to Dissolve Other Substances

Cohesion and Adhesion

 Cohesion   tendancy of molecules of the same kind to stick to one another Much stronger for water than other liquids  Adhesion  Attraction between unlike molecules Important to keep large groups of molecules organized in living world

Temperature Moderation

  Thermal energy  Total amt of E associated with the random movement of atoms and molecules in a sample of matter Temperature   Measure of the average E of random motion of particles in a substance Is temperature transferred from warmer to cooler or cooler to warmer?

 Warmer to cooler

Temperature Moderation

 Temperature rises bc the molecules move faster  In water, some of the E goes to break bonds, so doesn’t heat as fast  When you cool a substance the molecules slow and temp drops BUT  In water, it forms H bonds, so doesn’t cool as much as a metal

Examples of Temp Moderation of Water

 Oceans and lakes moderate the temperature of nearby land masses  El Nino  Evaporation and sweat

Low Density of Ice

 Formula for ice?

 Water is more dense than ice  Why?

 Hydrogen bonds  Longer lived bc slower moving than liquid form  Why is this important to living things?

Ability to Dissolve Other Substances

    Solution  Uniform mixture of 2 or more substances  Salt water Solute   Substance that is dissolved and present in a lesser amount salt Solvent   Substance that dissolves the other substance and is present in a greater amount water Aqueous solution  When chemical dissolved in water

Main Solvent

 Water is the main solvent in all cells and in plant sap  Polar molecules are easily broken down by water