MODULE C5: CHEMICALS OF THE NATURAL

ENVIRONMENT

Atmosphere• Molecular

elements (e.g. oxygen, nitrogen, ozone) and compounds (e.g.carbon dioxide, water)

• Monoatomic elements (e.g. argon)

hydrosphere

• Mainly water plus…

• Solution of ionic compounds (e.g. sodium chloride)

Q. Give the chemical symbols and state symbols for all the chemicals above.

PropertiesMolecular

compoundsIonic

compoundsMade from Two or more non-metal

atoms bondedMetal ions with non metal ions

Electrical properties

Insulators (no ions!) Conduct only when molten or dissolved in water

Forces holding them

together

Strong covalent bonds within the molecule but weak forces between molecules

Strong attractions between oppositely charged ions

Melting and boiling points

Low… found as gases at room temperature

High… found as solids or in solution

Formulae of salts• Metal ions (+) combine with non-metal

ions (-) to form neutral compounds.

• The formula of magnesium oxide is MgO

• The formula of sodium oxide is Na2O

Mg 2+

Mg 2+

Mg 2+

Mg 2+

Mg 2+

Mg 2+

O 2-

O 2-

O 2-

O 2-

O 2-

Mg 2+

O 2-

Na + O 2-

Na +

O 2-

O 2-

O 2-

O 2- O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

O 2-

Find the formula of… aluminium with fluorine,

calcium with chlorine, sulphur with potassium

The group number of the atom

can tell us which ion it will

form..

group ion

1 1+

2 2+

3 3+

4 None

5 3-

6 2-

7 1-

0 None

Lithosphere• Made of the crust and

upper mantle• Composed of minerals

e.g. quartz containing silicon dioxide found in granite and sandstone

• Rich in the atoms of silicon, oxygen and aluminium

Treasures of the Earth:

Gemstones for beauty, hardness, rarity

Chemical Brothers• Carbon dioxide and silicon dioxide are both covalently bonded

compounds but with very different physical properties

Carbon dioxide Silicon dioxide

Molecular structure (limited covalent bonding)

Giant structure (more extensive covalent bonding)

Low melting point High melting point

insulator Semi-conductor

gas Hard solid

Soluble in water Insoluble in water

negatively charged electrons are attracted to the positively charged nuclei to form strong covalent bonds

Extracting metals• For zinc, iron and copper (fairly un-reactive metals)

the ore (often an oxide) is mined, concentrated then the metal is extracted by heating with carbon

Copper oxide + carbon copper + carbon dioxide

lost oxygen gained oxygen

When oxygen is lost: REDUCTION

When oxygen is gained: OXIDATION

Re-write the equation above using symbols (chemical and state symbols!)

Write out the equivalent equation for iron (III) oxide (where iron has a 3+ charge)

Extracting reactive metals• The oxides of the more reactive metals are very stable so they

require large amounts of energy supplied by electricity in order to extract the metal. The electricity decomposes the compound into simpler substances.

Electrolyte: aluminium oxide (bauxite) with cryolite added

… in more detail• The cryolite

makes the aluminium oxide (bauxite) easier to melt so the ions in it are free to move to each electrode to become neutral atoms

Al 3+

Al 3+

Al 3+

O 2-

O 2-

O 2-

cathodeanode oxygen

gas released

Molten aluminium metal drops to the bottom

Use an ionic equation to show what happens at each electrode

Metals• The typical properties of high melting/

boiling points, high strength, malleable and conduction of heat/ electricity can all be explained by their structure

M + M +

M +

M +M + M +

M +

M + M +

Giant structure held together by ionic bonding

Metal ions in a lattice

Sea of electrons (free to move)

Environmental issues• The (i) mining, (ii) extraction,

(iii) transport, (iv) maintenance and (v) disposal of metals all have an impact on the environment.

• For each stage above suggest how it may affect the surroundings