Water

• Why are water molecules polar?

  • Electrons not shared evenly on outer shell
  • Greater the electron, the more negatives is and vice versa
  • Some regions more negative than others, and vice versa
• Explain polarity in water?

  • greater share of electrons in O-H bond
  • oxygen has a slightly negative charge due to unequal sharing of electrons
  • hydrogen slightly positive
  • negative and positive attract to form hydrogen bonds
• How are hydrogen bonds linked with polar water molecules?

  • N and P form hydrogen bonds
  • relatively weak interactions which break + reform between constantly moving water molecules
  • weak interactions BUT occur in high numbers
• Why is water liquid at room temperature?

  • has unusually high boiling temp
  • due to hydrogen bonding between water molecules
  • lots of energy is released to increase temp of water + for them to become gaseous
• What happens when water turns to ice?

  • becomes less dense than water
  • below 4C, hydrogen bonds polar molecules move further apart than average distance
  • produces a rigid but open structure with every oxygen atoms at the centre of the tetrahedral arrangement of hydrogen bonds
• What three properties does water have?

  • cohesive: moves as one mass because the molecules are attracted to one other e.g water up the plant
  • adhesion: water molecules attracted to other materials e.g lignin
  • Surface tension: water molecules much strongly attached to each other than air, so skin of surface tension
• Why does water act like a solvent?

  • It’s a polar molecule
  • many solutes can dissolve in it+ many are polar
  • medium for chemical reactions , transports dissolved compounds into and out of cell
• Why does water make a good transport medium?

  • cohesion
  • adhesion
  • leads to capillary action: water can rise up narrow tube against the force of gravity
• Why does water act like a coolant?

  • buffers the temp
  • as large amount of energy required to overcome hydrogen bonding
  • maintaining constant temps in cellular environment is important as enzymes only work at optimum temps
• Why can many organism not survive without water?

  • stable- does not change temp easily, does not turn into gas easily
  • ice floats creating an insulating layer
  • surface tension: small insects can live on top of the water.