Basic Chemistry

Water Chemistry

Atoms – 1 X 10-11

• Each atom is made up of a ‘nucleus’ and ‘orbits’ or ‘shells’ outside the nucleus Nucleus: Protons = + charged

Neutrons = neutral/ no charge

Orbits: Electrons = - charged

Periodic Table: A chart of elements that have been discovered

What makes each atom different, i.e. a unique element???

• Atomic number • The number of protons in nucleus • Electrons (-) will always equal protons (+)

• Atomic mass – The number of protons + neutrons in the

nucleus

Molecules = atoms bonded together = chemical bonds = represents ENERGY

wATER

METHANE

Ionic Bonds – between atoms that want to give and take electrons!

• “Happy” atoms = outer e- shells filled!

1. 2 e- fill first shell 1s What atom is this?

2. 8 e- fill second shell

1s 2s 2p What atom is this?

3. 8 e- fill third shell

?Q: Na and Cl … what would make them

Covalent Bonds = electrons shared

• CARBON

• Most common atom involved in covalent bonding

• ½ filled outer shell

(4 e-)

CH4 Methane gas

CompoundsNaCl – Sodium Chloride

- inorganic - ionic bonding - a salt

C6H12O6 - Glucose - organic

- covalent bonding- a sugar

Water Molecule: 2 Hydrogen and 1 Oxygen atom bonded

H20 - WATER

Oxygen side is slightly negative (-) charged

Hydrogen side is slightly positively charged (+)

Positive ends

Negative end

H H

O

“a polar-covalent molecule”

CAUSE and EFFECT

- Because of the ‘polarity’ of water molecules, they attract each other like magnets

• In this way, water molecules

“stick together” – cohesion

+-

-

+

+

+

Proof of the Cohesive nature of H2O …

- Certain insects can “walk on water”

- Cohesion between molecules of water

creates a strong surface tension

- benefits insects like the water strider

Adhesion - the tendency of two

DIFFERENT substances sticking together

Examples:

1. water molecules “sticking” to glass

2. capillary action

Capillary Action - example of adhesion

- water molecules adhere to the inside of tubules that fill the stems of plants

- water molecules are “drawn up” from the soil toward the top of the tree by the pull of adhesion

• Perspective: the size of “A” water molecule

– A molecule of water is so small that there are millions of molecules in a single drop of water.

– About 60 million water molecules could be stretched side by side across a penny.

Water• is the ONLY compound that commonly

exists in all 3 phases (solid, liquid, gas) on earth

• there would be no life on earth without water.

WATER … the Universal Solvent

In a SOLUTION, - the solvent is the substance that does

the dissolving ( usually a liquid)

- the solute is the substance that is dissolved (usually a solid)

- so many substances are soluble in water that it is therefore called the …

“universal solvent”

WATER … in living cells

- is the SOLVENT of our cells’ cytoplasm

- dissolves the SOLUTES: carbs, lipids, proteins

3 types of environments living cells encounter

• ISOTONIC environment

Equal amounts of solvent and solute molecules inside and outside of cells

• HYPERTONIC environment

– Greater % of solute molecules in sol’n outside the cell to

inside

• HYPOTONIC– Less % of solute molecules in the sol’n

outside the cell to inside

In Solutions … … water molecules disassociate into

1. H + ions and

2. OH- ions

THE pH Scale- a scale that measures the concentration of

H+ ions in the solution compared to OH- ions

1. An acidic solution (pH range 0 – 6.9)- a high concentration of H+ ions

- ( Infer: a low concentration of OH- ions )

Sulfuric acid

H2SO4

Citric AcidHC6H7O7

2. An alkaline solution - pH range 7.1 – 14 (also known as ‘bases’) - a low concentration of H+ ions compared to OH - ions

Sodium HydroxideNaOH Calcium carbonate

CaCO3

Sodium Bicarbonate

NaHCO3

• The pH scale ranges from 0 to 14

• The pH of pure water is 7 = equal amounts of H+ and OH- ions

Water Chemistry Terms

A. Hydrolysis- a chemical reaction where water

molecules are used to break up a large compound into smaller ones

B. Dehydration Synthesis- a chemical reaction where water

molecules are taken away from smaller molecules in order to form a larger compound.

Water Chemistry TermsC. Hydrophobic

- substances that will not dissolve in water

- Ex. fats, oils, soaps … “non-polar” substances

D. Hydrophilic - substances that will dissolve in water

• - Ex. sugar, salt, tea, protein powder - “polar” substances - “LIKE DISSOLVES LIKE”

Water’s UniquenessA. For most substances, their solid form is more

dense than the liquid formB. But for water the solid form is less dense than the liquid form. Proof: Ice floats on water!

WHY is ice less dense than water/steam? water as a solid

- the molecules “line up” - geometrically organized molecules

water as a liquid or gas

- molecules are random, in constant motion

- very close together

Pond Temperatures

VII. Water: Public Health Issues

A. Open Sewers

- Before the invention of sewer systems, human and animal waste was collected in open water ways.

- How many of the earth’s 6 billion people still live with these open sewers?

ANALYZE: Open Sewer Consequences

- breeds disease – why?

- contaminates drinking water – how?

- Hurricane Katrina “undid” the sanitation system … how?