Properties of Water- Honors Biology

Molecular Formula Water

H2O

Electronegative

the tendency to attract electrons to form a chemical bond

The hydrogen in water is.....

Slightly Positive

The oxygen in water is.....

Slightly negative

The bond that holds 1 water molecule together ( the 2 hydrogens to the 1 oxygen) is.....

Covalent

Polarity

Due to the unequal sharing of electrons

Result of Polarity

Water has amazing behaviors that allow life on plant Earth

How does water act?

Like a magnet- there are positive and negative poles

Oppositely charged poles will attract each other

Hydrogen Bonds

Very weak bonds; occurs when a slightly positive hydrogen atom in one molecule is attracted to the slightly negative atom in another molecule

Cohesion

When water molecules stick to each another due to hydrogen bonds

Surface Tension

A measure of how difficult it is to stretch or break the surface of a liquid

Due to hydrogen bonds in water

Adhesion

When water sticks to a different surface

Capillary Action

The movement of water upward against the force of gravity

Due to cohesion & adhesion working together

High Specific Heat

The ability of water to resist changes in temperature due the amount of energy required to break the hydrogen bonds

Why can water moderate temperatures?

High Specific Heat

Why is it hard to make water molecules move faster to increase its temperature ( think of trying to boil water)?

The hydrogen bonds keep the molecules stuck together.

How does water moderate temperatures?

- Absorbs heat energy- cooling the surrounding area when hydrogen bonds break

- Releases heat energy warming the surrounding area when hydrogen bonds reform

Why is ice less dense as a solid?

Water molecules move more slowly and the hydrogen bonds become more ordered. This gives the water a larger volume for the same mass and thus less density

crystal lattice structure

3D matrix that water forms as it becomes a solid

Why is important that water is less dense as a solid?

Ice floating allows life to go on underneath

If it didn't, the ice would settle at the bottom of the oceans and lakes and we would have a frozen planet

Universal Solvent

Water- due to its polarity and ability to dissolve many different solutes

Solute

A substance that is dissolved in a solution.

ex: Salt

Solvent

A liquid substance capable of dissolving other substances

ex: Water

Why is water a universal solvent?

The polarity of water allows it to dissolve most other substances, simply because most other substances encountered in living systems are themselves polar molecules, with positive and negative poles on them.

Why is it important that water is a universal solvent?

Easily allows organisms to move molecules around their bodies

Hydrophilic

water loving

Ex: Polar Molecules & ionic compounds

Hydrophobic

Water fearing

ex: non-polar molecules like oils and fats

Why doesn't oil and water mix

Polarity

Can water dissolve a fat such as oil? Why

No, because oil is nonpolar and hydrophobic. It does not have charges and therefore water can not stick to it to pull it apart and dissolve it.