Water and Life. Why Water?

Water: H 2 O

H H H H O S Water Hydrogen Sulfide Water and Similar Compounds H2SH2S H2OH2O

Hydrogen Sulfide: H 2 S

Water: H 2 O Hydrogen Sulfide: H 2 S

Boiling Point and Freezing Point F.P B.P liquid range Water (H 2 O) 0 o C 100 o C 100 o C Hydrogen Sulfide (H 2 S) -84 o C -60 o C 24 o C Hydrogen Selenide (H 2 Se) -64 o C -42 o C 22 o C Hydrogen Telluride (H 2 Te) -49 o C 2 o C 47 o C Water is the only substance that exists as a gas, solid, and liquid at ambient earth temperatures

H2OH2O Two hydrogen atoms One Oxygen atom

Hydrogen: 1 electron (-), 1 proton (+) Oxygen: 8 electrons (-), 8 protons (+) In water, the hydrogens shares their one electron with oxygen, which shares one of its electrons with each hydrogen. This sharing of electrons forms the bond between hydrogen and oxygen atoms to make the water molecule.

O H H Water Molecule O Shared electrons Bond of shared electrons H H Shared electrons

Water is Unbalanced by Oxygen

O H H Electrons are negatively charged, protons positive Oxygen is “electron greedy” Oxygen pulls electrons toward itself and away from hydrogen e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- This pulling of electrons toward itself is called “electronegativity” P+

O H e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- Abundant electrons (-) Two protons (+) H P+

+ + _ Red = lots of e - Blue = few e - + Polarity Electric Dipole (two poles): positive and negative

Consequences

N S Magnets and Polarity Magnetic Dipole

N S N S Polarity Attraction

N S N S Polarity Repulsion

Polarity N S N S

Slight negative charge Slight positive charge Polarity Electric Dipole - +

- + Orientation Bond - +

Hydrogen Bonding in Water

Implications  Liquidity  Excellent Solvent  Surface Tension  Density  Thermal Properties

Surface Tension

Density MVMV grams cm 3

Most substances are denser in their solid state than in their liquid state (the solid will sink in the liquid) Density

Low energy Closely packed Occupy small volume High Density High energy Loosely packed Occupy large volume Low Density

Low Energy Low Volume Dense High Energy High Volume Less Dense MV1MV1 MV2MV2

The lower the energy, the higher the density Energy corresponds to temperature Lower temperature, lower energy, close packing Solids have lower energy and higher density than liquids Solids sink in liquids Water is the exception. Lower temperature, close packing, higher density The density of pure water at 25 o C is g/mL. The density of ice at 0 o C is about g/mL.

liquid Crystalline Ice

High density Low density More molecules In a given volume Fewer molecules In a given volume

Importance

Thermal Properties Heat Capacity Heat and Temperature Change

alcohol water Thermometers

Heat Capacity When heat is added to water, the molecules speed up or vibrate more freely. This disturbs hydrogen bonds, but causes only a small change in temperature, because much of the heat energy is used to break or disrupt the hydrogen bonds 1 cal/g · o C The amount of heat input required to raise the temperature of a 1 g of a substance by 1 o C.

Water has a high heat capacity (ability to absorb heat without changing temperature) It requires 1 calorie of heat in 1 g of water to raise the temperature by 1 degree It requires 0.2 calories of heat in 1 g of sand to raise the temperature by 1 degree It requires 0.1 calories of heat in 1 g of iron to raise the temperature by 1 degree

Temperatures of large standing bodies of water remain relatively constant. Prevents wide temperature fluctuations