Chemistry 5

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CHEMICALS IN THE ATMOSPHERE

78% NITROGEN

 

21% OXYGEN

 

1% ARGON

 

0.04% CARBON DIOXIDE

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MOLECULAR SUBSTANCES

The atoms within the molecules are held together by very strong covalent bonds

The forces of attraction between these molecules are very weak

You only need a bit of energy to overcome the weak forces between the molecules

So they have low melting and boiling points

They're usually gases and liquids at room temperature

Pure molecular substances don't conduct electricity because there are no free electrons or ions

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COVALENT BONDING

Covalent bonding is where atoms share electrons with other atoms to form full shells

 

DIFFERENCES:

COVALENT: Non-metals & non-metals (&shares electrons)

IONIC: Metals & non-metals (&takes or gives electrons)

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CHEMICALS IN THE HYDROSPHERE

THE EARTH'S HYDROSPHERE IS THE OCEANS

The Earth's hydrosphere consists of oceans, puddles, lakes ect.

It also contains any compounds that are dissolved in water

Many of these compounds are SALTS (Group1 & Group7 compounds)

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CHEMICALS IN THE HYDROSPHERE

SOLID IONIC COMPOUNDS FORM CRYSTALS

Ionic compounds are made of ions

Ions with opposite charges are strongly attracted to one another & a GIANT LATTICE of ions builds up

There are ionic bonds between all of the ions

A single crystal of salt is one GIANT IONIC LATTICE

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CHEMICALS IN THE HYDROSPHERE

IONIC COMPOUNDS HAVE HIGH MELTING & BOILING POINTS

The forces of attraction between the ions are very strong

It takes a lot of energy to overcome these forces and melt the compound, even more to boil it

This makes them SOLIDS at room temperature

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IDENTIFYING CATIONS

ELEMENT                                      COLOUR FLAME

SODIUM                                         ORANGE/YELLOW

POTASSIUM                                            LILAC

CALCIUM                                                   RED

COPPER                                            BLUE/GREEN

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PRECIPITATION REACTION

When two solutions react to form an insoluable solid compound called a precipitate

ADD SODIUM HYDROXIDE:

"METAL"                      COLOUR OF PRECIPITATE

COPPER(II)                                        BLUE

CALCIUM                                           WHITE

IRON (II)                                             GREEN

IRON (III)                                    REDDISH BROWN

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TESTING FOR CARBONATES

You can test for carbon dioxide using limewater

 

TEST:

Bubble carbon dioxide through a test tube of limewater and if it goes cloudy you've identified a carbonate ion

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TESTING FOR SULFATES

ADD DILUTE HYDROCHLORIC ACID (TO GET RID OF ANY TRACES OF CARBON) FOLLOWED BY BARIUM CHLORIDE SOLUTION

A WHITE PRECIPITATE OF BARIUM SULFATE MEANS THE ORIGINAL COMPOUND WAS A SULFATE

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TESTING FOR HALIDES

ADD DILUTE NITRIC ACID (TO GET RID OF CARBONATE IONS) FOLLOWED BY SILVER NITRATE SOLUTION

HALIDE                 COLOUR PRECIPITATE            PRECIPITATE

CHLORIDE                                       WHITE                        SILVER CHLORIDE    

BROMIDE                                       CREAM                          SILVER BROMIDE    

IODIDE                                             YELLOW                        SILVER IODIDE        

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CHEMICALS IN THE LITHOSPHERE

THE LITHOSPHERE IS THE EARTH'S RIDGID OUTER LAYER - THE CRUST AND PART OF THE MANTLE BELOW IT

 

DIFFERENT TYPES OF ROCK CONTAIN DIFFERENT MINERALS AND ELEMENTS

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DIAMOND

The carbon atoms in diamonds each form four covalent bonds in a very rigid covalent structure

This structure makes carbon the hardest natural substance

All the strong covalent bonds give diamond a VERY HIGH MELTING POINT

It doesn't conduct electricity because it has no free electrons

It's insoluable in water

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GRAPHITE

Graphite is made from carbon and has a giant covealent structure.

Each carbon atom forms three covalent bonds, creating sheets of carbon atoms which can slide over eachother. This means graphite is slippery, so it's useful as a lubricant.

The layers are held together so loosely that they can be rubbed off on to paper and leave a black mark (how pencils work).

Graphite has a HIGH MELTING POINT

Only 3 of carbon's 4 outer electrons are used in bonds, so there are lots of spare electrons - conducts electricity - used for electrodes.

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SILICON DIOXIDE

Most of the silicon and oxygen in the Earth's crust exists as the compound silicon dioxide

Silicon dioxide is what sand is made of

Each grain of sand is one giant structure of silicon and oxygen

It has similar properties and structure to a diamond, e.g. high melting point & doesn't conduct electricity

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METALS FROM MINERALS

Metal ores are rocks that contain minerals from which metals can be extracted & in many cases the ore is an oxide of the metal.

Most metals need to be extracted from their ores using a chemical reaction, but a few unreactive materials, such as gold, are found in the Earth as the metal itself.

More reactive metals are harder to extract.

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CHEMICAL REDUCTION

A common way of extracting metal from its ore is chemical reduction using CARBON or CARBON MONOXIDE

When an ore is reduced, OXYGEN is removed

When a metail oxide loses its oxygen it is REDUCED & the carbon gains the oxygen and is OXIDISED

Metals that are more reactive than carbon can't be extracted by reduction and must be extracted by electrolysis

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ELECTROLYSIS

Electrolysis is the decomposition of a substance using electricity.

It needs a liquid to conduct the electricity - the electrolyte (usually free ions dissolved in water or molten ionic compounds).

Electrons are taken away from ions at the positive electrode and given to other ions at the negative electrode.

As ions gain or lose electrons they become atoms or molecules.

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CALCULATING MASSES

RELATIVE ATOMIC MASS - (top left number on element square)

RELATIVE FORMULA MASS - relative atomic masses added together

They can also be used to work out how much metal can be extracted from a ore.

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METALS

Metal ions consist of a giant structure.

Metallic bonds involve free electrons which produce all the properties of metals.

These free electrons come from the outer shell of every metal atom in the structure.

The positively charged metal ions are held together in a crystal by a sea of free electrons that can move.

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METAL PROPERTIES

1) THEY'RE GOOD CONDUCTORS OF HEAT & ELECTRICITY

2) MOST METALS ARE STRONG & MALLEABLE - Metallic bonds mean metals have a high TENSILE strength (they're strong & heard to break)

3) THEY GENERALLY HAVE HIGH MELTING & BOILING POINTS - They're very strong so it takes a lot of energy to break them.

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ENVIRONMENTAL IMPACT

There is a limited amount of ores and people have to balance the social, economic and environmental effects of mining the ores.

Mining metal ores is good  because useful products can be made and it provides jobs and brings money in to the economy.It also means that services such as health can be improved.

Mining ores is bad for the environment though as it uses a lot of energy, scars the landscape and destroys habitats. Deep mine shafts can also be dangerous for a long time after the mind has been abandoned.

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ENVIRONMENTAL IMPACT

Mining and extracting metals takes a lot of energy, mostly from burning fossil fuels.

Fossil fuels are running out so it's important to conserve them & burning them contributes to global warming, acid rain and climate change.

Recycling saves money too, because energy isn't cheap.

There is a finite amount of metal in the Earth and recycling conserves these resources.

Recycling metal cuts down the amount of rubbish that gets sent to landfills, which saves spaces and prevents pollution.

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