A1.1: Water

Is water polar or non-polar?

Is water polar or non-polar?

Polar

Polarity of molecules depends on:

Equal or unequal sharing of electrons

Polar molecule

Electrons shared unevenly: different charges at each “end”

Non-polar molecule

Electrons shared evenly

Covalent bonds

Two atoms share electrons

Properties of water

• Polar

• Provides buoyancy

• Provides stable thermal properties

• Higher viscosity than air

Water molecule polarity diagram

Hydrogen bonds

Ephemeral attraction between water molecules. The oxygen bonds to one of the hydrogens.

Cohesion

Molecules of the same type are attracted to each other

Hydrogen bonds below freezing point

Molecular motion slows until it stops, hydrogen bonds become locked into place

Liquid water molecules affect on each other

Influence each other, but not to the point where they stop. Gives water some of its more interesting properties.

Surface tension

Property allowing water to resist - causes pain during belly flops and allows bugs to walk on water

Surface tension cause

Water molecules at the surface of a body of water do not have water molecules above them, so nothing is pulling them up, and they have a quite strong cohesive force to the water molecules around and below them.

Water column (cohesion)

Evaporation and cohesion in water molecules causes tension which pulls on water molecules further down in the xylem where water is evaporating from, and cohesion causes all the water molecules to move upwards in a “water column.”

Adhesion

Attraction and hydrogen bonding between two different types of molecule.

Water column (adhesion)

When the water column is not actually being “pulled up,” adhesion between water molecules and cellulose in the plant cell wall allows the column to not fall back down again.

Cuticle (plant)

Wax layer preotecting the leaf from excessive evaporation

Capillary action

Water entering small spaces resisting gravity (for example moving up through soil and into plants)

The asteroid theory

Earth was too hot to retain or form water, but over long periods of time it cooled and asteroid collisions (which would have been common back then) brought hydrated minerals which released water that became part of the Earth’s crust.

Heavy water

Water molecule where the hydrogen atom contains a neutron.

Deuterium

Hydrogen atom containing a neutron

Ratio of heavy to typical water on Earth

Typical water is far more common: ratio in oceans is similar to that of many asteroids.

Cytoplasm soluble molecule examples

• Cytoplasmic enzymes

• Glucose

• Ions

• Amino acids

• Proteins

Cytoplasm insoluble molecules examples

• Steroid hormones

• Membrane-bound proteins (can stay attatched to membrane and still interact with other molecules.

The first cells originated in water: true or false?

True

Goldilocks zone

The area in a solar system that allows for water to exist and be retained on a planet based on temperature and gravitational pull