All revision notes for c5

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C5 - Chemicals of the Natural Environment
Chemicals in the Atmosphere
The Earth's atmosphere is made up of many gases. Some of these gases are elements, e.g. oxygen
(O2), nitrogen (N2) and argon (Ar) ­ they contain only one type of atom.
Other gases are compounds, e.g. carbon dioxide (CO2) ­ they contain more than one type of atom
bonded together.
There are different amounts of each of these gases in the atmosphere- it is about 78% nitrogen,
21% oxygen, 1% argon and 0.04% carbon dioxide. Most of the gases in the atmosphere are
molecular substances.
Molecular Substances
Molecular substances usually exist as small molecules, like CO2 and H2O. The atoms within the
molecules are held together by very strong covalent bonds.
In contrast, the forces of attraction between these molecules are very weak. You only need a little
bit of energy to overcome the weak forces between the molecules ­ so molecular substances have
low melting and boiling points, meaning that they are usually gases and liquids at room temperature.
Pure molecular substances don't conduct electricity because their molecules aren't charged. There
are no free electrons or ions. Most non-metal elements and most compounds formed from
non-metal elements are molecular.
Chemicals in the Hydrosphere
The Earth's hydrosphere consists of all the water in the oceans, seas, lakes, rivers. It also contains any
compounds that are dissolved in the water. Many of these compounds are ionic compounds called
salts. Examples of salts are sodium chloride (NaCl), Magnesium chloride (MgCl2) and potassium
bromide (KBr).
Ionic Compounds
Ionic compounds are made of charged particles called ions. Ions with opposite charges are strongly
attracted to one another. You get a giant lattice of ions build up. There are very strong chemical
bonds called ionic bonds between all the ions. A single crystal of salt is one giant ionic lattice, which is
why salt crystals tend to be cuboid in shape.
The forces of attraction between the ions are very strong. It takes a lot of energy to overcome these
forces and melt the compound, and even more energy to boil it. So ionic compounds have high
melting and boiling points, which makes them solids at room temperature.
When an ionic compound dissolves, the ions separate and are all free to move in the solution. This
means that they're able to carry an electric current. Similarly, when an ionic compound melts, the ions

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When an ionic compound is solid, the
ions aren't free to move, and so an electrical current can't pass through the substance.
Chemicals in the Lithosphere
The lithosphere is the Earth's rigid outer layer ­ the crust and part of the mantle below it. It is made
up of a mixture of minerals, often containing silicon, oxygen and aluminium. Different types of rock
contain different minerals and different elements. For example, limestone contains a lot of calcium,
whereas sandstone contains a lot of silicon.…read more

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Hydrogen needs just one extra electron to fill its outer shell. So, two hydrogen atoms shared their
outer electron so that they have a full shell, and a covalent bond is formed.
Carbon dioxide needs four more electrons to fill up its outer shell. Oxygen needs two. So two
doubled covalent bond are formed. A double covalent bond has two shared pairs of electrons.
Identifying Positive Ions
Compounds of some metals give a characteristic colour when heated. This is the idea behind flame
tests.…read more

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Ag+(aq) + Cl-(aq) = AgCl(s). A chloride gives a white precipitate of silver chloride
Ag+(aq) +Brl-(aq) = AgBr (s). A bromide gives a cream precipitate of silver bromide
Ag+(aq) + I-(aq) = AgI(s). A iodide gives a yellow precipitate of silver iodide
Metals from Minerals
Rocks are made of minerals. Minerals are just solid elements and compounds. Metal ores are rocks
that contain varying amounts of minerals from which metals can be extracted. In many cases the ore is
an oxide of the metal.…read more

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Electrolysis is the decomposition of a substance using electricity. It needs a liquid to conduct the
electricity ­ called the electrolyte.
Electrolytes are usually free ions dissolved in water or molten ionic compounds. It's the free ions that
conduct the electricity and allow the whole thing to work. For an electrical circuit to be complete
there has got to be a flow of electrons.…read more

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Metallic bonds mean metals have a high tensile strength ­ they are strong and hard to break. The
layers of atoms in a metal can slide over each other, making metals malleable ­ they can be
hammered or rolled into flat sheets.
Metallic bonds are very strong, so it takes a lot of energy to break them ­ you have to get the metal
very hot to melt it.…read more


Sasha Dean

Thanks- A very good, thorough revision booklet (papers!).

Hope i get an A*.

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