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GCSE Chemistry
C5: Chemicals of the natural environment
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What chemicals are found in the atmosphere
and what properties do they have?
Nitrogen (78%) ~ Atomic mass 39.948 g.mol -1
Has 4 isotopes ~ Other (1%) e.g. Carbon Dioxide
Melting point -210°C ~ Melting point -55.6°C
Boiling point -195.8°C
~ Boiling point -78.5°C
Atomic no. 7
Atomic mass 14.0067 g.mol -1
Oxygen (21%)
Has 4 isotopes
Melting point -219°C
Boling point -183°C
Atomic no. 8
Atomic mass 15.999 g.mol -1
Argon (<1%)
Has 6 isotopes
Melting point -189°C
Boiling point -185.7
Atomic no. 18
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What chemicals are found in the lithosphere, what type of
bonding is involved and how is this related to their typical
Oxygen (47%)
Silicon (28%)
Aluminium (25%)
Most of the oxygen and silicon form silicon dioxide (SO2) which is more commonly
known as sand. This is formed by what known as a giant covalent bond. Normally
because a covalent bond is a weak one, the compound formed would have a low
melting point; however silicon dioxide is different and because of this giant
covalent bond it has a high melting point. It also does not dissolve in water, is
very hand and it does not conduct electricity.
Different types of rock contain different minerals and different elements. For
example limestone contains a lot of calcium whereas sandstone contains a lot of
Some minerals are a lot rarer than others and this makes them more valuable.
These are called gemstones and some examples would be gems like rubies,
sapphires and diamonds. Gemstones are very hard and like silicon dioxide, they
have a giant covalent bond. They are also pretty and sparkly and this is mostly
what makes them so attractive to own (it's not all about the money).
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Slide 4

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Describe which chemicals make up the biosphere and
state what elements make up the molecular compounds
The biosphere is made up of six main elements. Nitrogen, carbon, hydrogen,
oxygen, phosphorus and sulphur. These elements make up the compounds of
carbohydrates, fats, proteins and DNA. Carbohydrates are the main source of
energy our body uses. It makes us feel full and keeps us going for longer because
it lets out it's energy slowly. Fats insulate us and are also another form of energy
our body uses. Proteins, are again a source of energy and as well as keeping you
fuller for longer, they also help burn fat. DNA is the reason we are who we are.
These have individual genes in saying which hair/eye colour we have etc...
It is possible to recognise molecules by the elements they contain.
1. DNA always contains phosphorus and sulphur
2. Proteins always contain nitrogen and may also contain sulphur
3. Fats and carbohydrates only contain carbon, hydrogen and oxygen... You can
tell them apart because fats contain more carbon.
Carbohydrates, proteins and DNA are all molecular.
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Why is the hydrosphere `salty'?
The hydrosphere is `salty' because the sea contains ionic compounds (salts) which
dissolve. Some examples of salts are sodium chloride, magnesium chloride and
potassium bromide.
Rain (which is fresh water) falls from clouds onto the land and finds its way into
lakes and rivers, and also through the ground, back to the sea, picking up salts
and minerals as it goes. Once it reaches the sea, the water can be evaporated
again to form new clouds containing fresh water, and the salt is left behind, so
over millions of years the oceans have slowly been accumulating salt washed off
the land by fresh water. However, the sea does not continue to get saltier
because chemical reactions take place to equal out the amount that is still being
brought in by the streams and rivers.
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Slide 6

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Explain the properties of salts using ionic
Because of ionic bonding ­ when positively and
negatively charged atoms attract each other ­ salts have
a very high melting point. For example Sodium Chloride
­ NaCl (Na+ and Cl-) ­ has very strong attractive forces
between the ions and so it takes a lot of energy to break
it down. This is why NaCl has to be heated to 808°C
before it melts.
Salts dissolve in water because the ionic bonds are
weakened by it, allowing the ions to mobilize. This is
why electrolysis works.
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