Water Ch.2 AP Biology

covalent bonds

when two nonmetal atoms SHARE electrons to have a full valence shell

Polarity

uneven distribution of electrons amongst atoms in a molecule

Hydrogen Bonds

Weak, magnetic-like attraction between molecules

• important in water

  • oxygen hogs electrons cuz of negative charge

    • this oxygen hydrogen bonds w/ other hydrogens

  • this is why water is cohesive

Capillary Action

Tendency of water to rise up thin tubes

• VERY important for life

  • water moves from roots to leaves

    • adheres to inner walls of tubes

    • cohesion pulls water up and out as transpiration

Nonpolar Covalent

Two nonmetals share electrons EQUALLY

• similar electronegativites

• neither atoms shares electron more strongly than the other

Polar Covalent

Two nonmetals share electrons UNEQUALLY

• electronegativity difference

  • in water, oxygen is more electronegative (allows hydrogen bonds with neighboring water molecules)

Hydrophilic

Water-loving substance (interacts readily)

• Polar molecules

  • easily form hydrogen bonds with water

  • e.g. table salt/sugar

Hydrophobic

Water-hating substances (repels water)

• Nonpolar molecules

  • can’t form hydrogen bonds w/ water

  • e.g. oil

Surface Tension

How easy it is to break a liquid’s surface

• Water has HIGH surface tension due to hydrogen bonds

  • think why belly flops hurt

Temperature

measure of kinetic energy of WHOLE OBJECTS

Thermal energy

Measure of total amount of kinetic energy INSIDE OBJECTS (molecular-level)

• movement of atoms inside water

  • ice has little thermal energy

Solvent

Dissolver

• water is the best at dissolving substances due to its polarity (forms hydrogen bonds easily)

Solute

Dissolvee

(getting dissolved)

Acids

Increase H+ concentration in water

• When acids dissolve in water, it donates H+ ions

  • lowers pH

Base

Reduce H+ concentration in water

• When it dissolves, it either accepts H+ OR releases hydroxide ions (OH-) to form water

  • NaOH releases OH-, which pulls H+ out of the solution and makes it less acidic