Water Chapter 3 Section 1

Objectives Describe the structure of a water molecule. Explain how water’s polar nature affects its ability to dissolve substances. List two of water’s properties that result from hydrogen bonding.

Polarity A polar molecule has an uneven distribution of charge The electrons spend more time around one of the atoms than the rest. Around which atom do you think the electrons spend more time? Why?

Polarity The electrons spend more time around the oxygen atom due to the stronger attraction to the larger number of protons in the nucleus.

Polarity The polar nature of water makes it effective in dissolving other polar substances like sugars, some proteins and ionic compounds.

Relevance? The dissociated ions are free to participate in many biological reactions. Dissolved ions are necessary for such functions as muscle contractions or nerve impulse transmission.

Hydrogen Bonding The polar nature causes it to be attracted to other water molecules. The weak attraction that holds water molecules together is called hydrogen bonding. H-bonds are easily broken (comparatively).

Hydrogen Bonding H-bonding allows for 4 critical properties of water: 1. cohesion- attractive force between particles of the same kind 2. adhesion- attractive force between different particles

Hydrogen Bonding 3. capillarity- water moving upward through a narrow tube against the force of gravity. 4. temperature moderation- water must gain or lose a relatively large amount of energy for its temperature to change.

POP-QUIZ!!!!!!

Why is such a large amount of energy required for the temperature of water to change?

Answer: Because most of the thermal energy that the water initially absorbs breaks the hydrogen bonds between the molecules. After that, the thermal energy can increase the motion of the molecules and raise the T of the water.