oxygen shares its two unpaired electrons with two hydrogen atoms water’s molecular structure:

CovalentBond

CovalentBond

Oxygen shares its two unpaired electrons with two hydrogen atoms

Water’s Molecular Structure:

Polar Covalent Bonds:A covalent molecule that has a slight positiveand negative charge on opposite ends.Example:

Water

*in a polar covalent bond, one atom is moreelectronegative than the other.

Electronegativitythe tendency for an atom to attract electrons

Solubility•Polar charges attract it to other polar molecules

•sugars, ionic compounds (like salt), and some proteins

•Not attracted to nonpolar substances like lipids (fats)

http://www.questacon.edu.au/html/squad_activities/assets/images/oil-and-water.jpg

Hydrogen Bonds:•Weak, polar covalent bonds.•Form rapidly and break rapidly

Example:Between water molecules

H-Bonding explains unique properties: cohesion, adhesion, high heat capacity, evaporative cooling, the low density of ice, the ability of water to dissolve many substances

http://www.realeyz.com/photo/macro/photos/leaf_drops.jpg

CohesionMolecules of the same substance are attracted to each other

•Leads to surface tension and water droplets

AdhesionAttraction between molecules of different substances

Ex: glass and water

http://staff.um.edu.mt/rlib1/sm/wpe32.jpg

CapillarityAttraction that causes the surface of the liquid to rise when in contact with a solid.

Cohesion-Adhesion Theory

-As water evaporates from leaves, it tugs on the water molecules below-Cohesion and adhesion pull water up and replace missing water molecules-Water enters the roots by osmosis

www.emc.maricopa.edu/.../BioBookPLANTHORM.html

Did you ever wonder: How does water move from roots to leaves when a tree doesn’t have a heart to pump the water?

Denisty of Ice•Most solids are more dense than their liquids

•This makes solids sink

•Ice is less dense than liquid water

•Due to H-Bonds•Important to life because bodies of water freeze top down•Allows life to survive below

http://shiftingbaselines.org/blog/images/Iceberg.jpg

pH ScaleMeasurement of the concentration of hydrogen ions

Acid:High concentration of [H+](or hydronium ion);low conc. of [OH-]

Base:High [OH-](a.k.a. hydroxide ion);low [H+]

pH = -log [H+]

Stomach Acid = pH 2