1.1 Structure of Water and Hydrogen Bonding

Properties of water

Most important: Polarity, High specific heat capacity, High heat of vaporization, Cohesion, Adhesion, Surface tension

Capillary action, density, universal solvent

Polarity

Polar covalent bonds created by unequal sharing of electrons between oxygen and hydrogen within the molecule of water

Caused in water by the difference in electronegativity between oxygen and hydrogen

Contributes to hydrogen bonding between and within biological molecules

allows for adhesion, cohesion, and surface tension

Electronegativity

the measure of an atom’s ability to attract electrons to itself

Large differences in electronegativity creates ionic bonds

Moderate differences create polar covalent bonds

Small differences create nonpolar covalent bonds

Hydrogen bonds

the partially positive hydrogen atom in one polar covalent molecule will be attracted to an electronegative atom in another polar covalent molecule

an intermolecular bond(bond that forms between molecules, not created, molecule to molecule, weak bond and forms quick which is good for us

Happens because when a hydrogen atom is bonded to an electronegative atom the electrons are not being shared equally between atoms(polar covalent bond), which causes the hydrogen to have a partial positive charge and the electronegative atom to have a partial negative charge

Covalent bonds

when two or more atoms share electrons

forms molecules and compounds

formed WITHIN the water molecule not between 2 water

2 types: nonpolar and polar

Nonpolar covalent

electrons are shared equally between two atoms

Hydrophobic

Water cannot dissolve non polar bonds

Polar covalent

electrons are not shared equally between two atoms

WITHIN the water molecule

Hydrophilic

Water’s Polarity allows it to dissolve ionic and polar compounds because the partially positive and partially negative ends of water interact with polar molecules and ions, helping disperse the molecules and ions in the solution

High specific heat capacity

H2O resists changes in temperature because the of hydrogen bonds

Heat must be absorbed to break hydrogen bonds, but heat is released when hydrogen bonds form

This moderates air temperature(large bodies of water can absorb heat in the daytime and release heat at night), stabilizes ocean temperature(benefits marine life), and organisms can resist changes in their own internal temperature

High heat of vaporization

Water requires a large amount of energy to evaporate due to strong hydrogen bonds

Evaporative cooling: as water molecules evaporate, the surface they evaporate from gets cooler

This moderates Earth’s climate, stabilizes temperature in lakes and ponds, prevents terrestrial organisms from overheating(ex sweating), and prevents leaves from becoming too warm in the sun

Adhesion

the attraction to other molecules that are polar or have charge (H2O to other molecules)

due to the polarity of H2O

Allows water to cling to the cell walls to resist the downward pull of gravity in plants

Cohesion

attraction of molecules for other molecules of the same kind (H2O to H2O)

Hydrogen bonds between H2O molecules hold them together and increase cohesive forces

Allows for the transport of water and nutrients against gravity in plants

allows for transpiration in plants

Responsible for surface tension

Surface tension

surface H2O molecules experience greater inward pull because there are no molecules above them to balance the forces

allows bugs to walk on water

Capillary action

the upward movement of water due to the forces of cohesion, adhesion, and surface tension

occurs when adhesion is greater than cohesion

important for transport of water and nutrients in plants

Density

as water solidifies it expands and becomes less dense

ice floats because it has low density

due to the hydrogen bonds

when cooled, H2O molecules move too slowly to break the bonds

Allows marine life to survive under floating ice sheets

Hydrogen bonds cause water molecules to form a crystalline structure

If ice was more dense, it wouldn’t float and would freeze from the bottom up

Universal solvent

Solvent is the dissolving agent in a solution

Water is considered a universal solvent because it can dissolve many substances

its polar molecules are attracted to ions and other polar molecules it can form hydrogen bonds with

the partially positive and partially negative ends of water interact with polar molecules and ions, helping disperse the molecules and ions in the solution

“like dissolves like”

water can interact with sugars or proteins containing many oxygen and hydrogen

water will form hydrogen bonds with the sugar or protein to dissolve it

dissolves ions

does NOT dissolve non polar molecules