Water

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Water

• Essential Molecule for Life

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Why is water so important?

• Life on Earth probably evolved in the water.
• Living cells are 70 - 95 water
• Water covers 75 of the Earth

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In Water...

• 2 hydrogen atoms are joined to 1 oxygen atom by
  POLAR COVALENT bonds
• The electronegative oxygen nucleus pulls shared
  electrons towards itself and away from the
  hydrogen nuclei

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Water is a Polar Molecule

• Oxygen has a slight negative charge (-)
• Hydrogen has a slight positive charge ()
• The polarity of these bonds and its asymmetric
  shape make the water molecule a POLAR MOLECULE

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Water Molecules
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Each water molecule can form up to 4 Hydrogen
bonds which holds the molecules together.
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Properties of Water

• 1. Water is cohesive
• Hydrogen bonding of water molecules provides
  COHESION
• One water molecule sticking to another
• EX. Transport in Plants upward pull of water
  molecules in plant veins

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Properties of Water

• 2. Water is Adhesive
• Water can cling to substances
• EX. Adhere to walls of vessels against the pull
  of gravity (straw)

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Properties of Water

• 3. Water has a greater surface tension than most
  other liquids (H-bonds)
• Surface Tension a measure of how difficult it
  is to stretch or break the surface of a liquid
• EX. Water Strider, Skipping a rock

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Properties of Water

• 4. Waters Temperature - Stabilizing Effects
• High Specific Heat of 1
• Specific Heat amount of heat that must be
  absorbed or lost for 1 gram of that substance to
  change temp. by 1 degree Celsius
• Water can stabilize temp. because it can absorb
  considerable heat before its temp changes.
• This is important when it comes to Evaporating
  Freezing

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Evaporation Vs. Freezing

• Hydrogen Bonds are constantly forming and
  breaking between water molecules
• More Broken Evaporation
• More Formed Freezing

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Properties of Water

• 5. High heat of Vaporization
• Heat of Vaporization the quantity of heat a
  liquid must absorb for 1g of it to evaporate
• Water has a high heat of vaporization because of
  Hydrogen Bonds
• Water is LESS dense as a solid. As it solidifies
  it expands
• Water freezes when molecules do not move fast
  enough to break H-bonds

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What would happen if ice was more dense than
water?

• Ice would Sink
• Oceans would freeze solid
• Aquatic and Marine Biomes would change drastically

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Waters Stats

• Freezing Point O C, 32 F
• Boiling Point 100 C, 212 F
• Room Temp. 20-25 C, 70-75 F
• Body Temp. 37 C, 98.6 F

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When you bring 2 objects of different temp.
together, which direction does heat pass?

• From the warmer to the cooler until the
  temperatures are equal
• EX. An ice cube absorbs heat causing it to melt

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Water is a versatile solvent

• Liquid with 2 or more substances Solution
• The dissolving agent is called the Solvent
• The substance being dissolved is called the Solute

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Ionic Compounds Dissolve in Water

• NaCl dissociates into Na and Cl-
• The oxygen regions of water molecules have a
  negative charge and cling to the Na
• The hydrogen regions of water molecules have a
  positive charge and cling to the Cl-

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Polar Compounds Dissolve in Water

• Any substance that has an affinity for water is
  Hydrophilic (Water Loving), even if it doesnt
  dissolve (ex. Cotton - made of cellulose, absorbs
  water)
• Any substance that does NOT have the affinity for
  water is Hydrophobic (Water fearing) non ionic,
  non polar substances repel water (ex. Vegetable
  oil)

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Hydrophobic
Hydrophilic
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Humans and Water

• Drinking water fit for consumption is called
  potable water
• Water helps regulate and maintain your body
  temperature, transports nutrients and oxygen,
  removes waste products, and moistens your mouth,
  eyes, nose, hair, skin, joints, and digestive
  tract.

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Water and Humans

• Limiting your water intake can result in
  dehydration, elevated body temperature, fatigue,
  decreased performance, and increased risk of
  heat-related illness.
• Consume at least ten 8-ounce glasses of water per
  day.

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Put in your NOTECARDS

• The Five (5) properties of water
• 1 NOTECARD