Chapter 3 - Water And Life + Test Review Flashcards
What is electronegativity, and how does it affect interactions between water molecules?
Electronegativity is the attraction of an atom for the electrons of a covalent bond. Because oxygen (3.5) is more electronegative than hydrogen (2.1) the oxygen atom in H2O pulls electrons towards itself, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. Atoms in neighboring water molecules with opposite partial charges are attracted to each other, forming a hydrogen bond.
Why is it unlikely that two neighboring water molecules would be arranged like this?
H H / \ O O \ / H H
The hydrogen atoms of one molecule, with their partial positive charges, would repel the hydrogen atoms of the adjacent molecule.
What would be the affect on the properties of the water molecule if oxygen and hydrogen had equal electronegativity?
The covalent bonds of water molecules would not be polar, and the water molecules would not form hydrogen bonds with each other.
What is a polar covalent bond?
A bond in which electrons are shared unequally. The shared electrons are pulled closer to the more electronegative atom making it slightly negative and the other atoms more positive.
What is a polar molecule?
A molecule with an uneven distribution of charges in different regions of the molecule. Example - H2O - O has a partial negative charge and H a partial positive charge.
What is a hydrogen bond?
Oppositely charged regions of neighboring water molecules are attracted to each other. The electrons spend more time near O than H.
Describe how properties of water contribute to the upward movement of water in a tree.
Hydrogen bonds hold neighboring water molecules together. This cohesion helps chains of water molecules move upward against gravity in water conducting cells as water evaporates from the leaves. Adhesion between water molecules and the walls of the water conducting cells also helps counter gravity.
What are the four properties of water?
1) Cohesion
2) Temperature stabilizing capacity
3) Insulation of bodies of water by ice (Expansion upon freezing)
4) Solvent properties
Explain cohesion.
The linking together of like molecules, often by hydrogen bonds (which hold water molecules together). Also helps the transport of water and other dissolved nutrients against gravity in plants.
What is adhesion?
The clinging of one substance to another. An attraction between different substances. Example - water and plant cell walls.
What is surface tension?
A measure of how difficult it is to stretch or break the surface of a liquid. (Due to hydrogen bonding, water has a high surface tension)
Explain how water moderates air temperature.
Water moderates air temperature by absorbing heat from air that is warmer and releasing stored heat to air that is cooler (with only a slight change to its own temperature).
What is kinetic energy?
The energy of motion.
What is thermal energy?
The kinetic energy associated with random motion of atoms or molecules.
What is temperature?
A measure of energy that represents the average kinetic energy of the molecules in a body of matter.
Define heat.
Thermal energy in transfer from one body of matter to another.
What is a calorie?
The amount of heat required to raise the temperature of 1g of water by 1 degree C. And also the converse.
What is a kilocalorie?
1,000 calories. The quantity of heat required to raise the temperature of 1 kg of water by 1 degree C.
Define specific heat.
The amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1 degree C.
What is the specific heat of water? Explain it’s importance.
1 calorie / g / degree C
- Water has a high specific heat and resists changing its temperature due to excessive hydrogen bonding
- Heat must be absorbed in order to break hydrogen bonds
- Heat is released when hydrogen bonds form
- The high specific heat of water keeps temperature fluctuations on land and in water within limits that permit life
