Unit 1 - Biochemistry (Chemical Bonds, Water, pH & Buffers)

Covalent bond

Atoms share electrons to fill valence shells forming strong stable molecules

Nonpolar covalent bond

Electrons shared equally so no partial charges form

Polar covalent bond

Electrons shared unequally creating partial charges due to electronegativity

Electronegativity

Ability of an atom to attract electrons

Water polarity

Oxygen pulls electrons more creating partial negative O and positive H

Hydrogen bond

Weak attraction between partial positive H and partial negative O

Why hydrogen bonds matter

Many together create strong effects in water

Cohesion

Hydrogen bonds make water stick to itself creating surface tension

Adhesion

Water sticks to other surfaces due to hydrogen bonds

Capillary action

Cohesion pulls water up and adhesion helps it climb surfaces

Surface tension

Cohesion at surface creates resistance

Water as solvent

Polarity lets water surround and separate ions and polar molecules

Hydrophilic

Polar or charged substances that dissolve in water

Hydrophobic

Nonpolar substances that do not dissolve in water

Ice less dense

Hydrogen bonds space molecules farther apart in solid water

Why ice floats

Lower density keeps ice on top insulating water below

High specific heat

Hydrogen bonds absorb heat so water resists temperature change

Why high specific heat matters

Stabilizes climate and body temperature

Heat of vaporization

Water needs lots of energy to evaporate due to hydrogen bonds

Evaporative cooling

Evaporation removes heat cooling surfaces

Water ionization

Water splits into H plus and OH minus

pH

Measure of hydrogen ion concentration

Acid

High H plus concentration

Base

Low H plus concentration

Neutral

Equal H plus and OH minus

pH scale logarithmic

Each pH change equals ten times change in H plus

pH example

Two pH units equals one hundred times difference in H plus

Why pH matters

pH changes protein shape and function

Buffer

Stabilizes pH by absorbing or releasing H plus

Buffer function

Prevents sudden pH changes in cells