AP Biology - 1.1 Structure of Water + Hydrogen Bonding

What is a covalent bond?

A bond where atoms share electrons

Identify the partial charge of an H₂O Molecule? Explain.

• Oxygen is negative

• Hydrogen is positive

• Oxygen is more electronegative than Hydrogen, so more electrons are attracted to Oxygen giving it a partial negative charge and giving Hydrogen a partial positive charge

what are the 4 emergent properties of water?

• versatility as a solvent

• ability to moderate temperatures

• cohesive/adhesive behavior

• expansion upon freezing

Define electronegativity

the tendency of an atom to attract electrons in a molecule

Define polarity

an uneven distribution of electrons in a molecule

What are hydrogen bonds?

a weak bond between the positive and negative regions of 2 separate molecules

define cohesion:

attraction between molecules of the same substance

define adhesion:

attraction between molecules of different substances

how do cohesive/adhesive forces contribute to sustaining life?

• as water vapor molecules leave, the pull the water molecules at the bottom a step upwards through TRANSPIRATION

• because of the hydrogen bonds holding them together, the water molecules stay attracted to each other as they travel up through cohesion

• capillary action - movement of liquid through a material against an opposing force

how does cohesive/adhesive behavior lead to surface tension?

• a measure of how difficult it is to break the surface of a liquid

• water has an unusually high surface tension due to hydrogen bonding of water molecules at the air-water interface (bonds held together very tightly —> more stable + less dynamic)

how does surface tension help sustain life?

• certain creatures, such as spiders, can take advantage of surface tension of water to walk across a pond without breaking the surface

define high heat capacity:

• water has a very high specific heat - water can absorb or release a large amount of heat w/ only a slight change in its own temperature

• due to hydrogen bonding

define evaporative cooling:

• as liquid evaporates, the remaining surface cools down

• hydrogen bonds must be broken for liquid to evaporate

how does evaporative cooling help sustain life?

• in a body of water, water molecules with highest amount of KE and highest temperature will leave first —> prevents overheating of water body and of animals living in the water

how does high heat capacity help sustain life?

• minimizes temperature fluctuations to within limits that permit life

heat is absorbed and released when hydrogen bonds —(1)— and —(2)—

(1) form, (2), break

net release of energy

define expansion upon freezing and explain how it helps sustain life:

• hydrogen bonds lead to ice having a crystallite structure where the water molecules are held at “arm’s length” —> so, ice is less dense than water

• because ice can float it insulates the liquid water below and prevents animals from dying from freezing temps

• also, water bodies only freeze at surface rather than throughout the entire ocean

define solution:

a liquid that is completely homogeneous mixture of substance

define solvent:

the dissolving agent of a solution

define solute:

the substance that is dissolved

define aqueous solution:

a solution in which water is the solvent

what is water’s versatility as a solvent due to?

polarity

what types of compounds can dissolve in water?

ionic and nonionic polar

what is a hydration shell?

the sphere of water molecules around each dissolved ion

how does water’s versatility as a solvent contribute to its ability to sustain life?

• wherever water is traveling through the ground or body, it collects and carries important nutrients, minerals, etc

distinguish between hydrophobic and hydrophilic

• philic - affinity for water

• phobic - no affinity for water