Chemistry unit 1

All substances are made of atoms. An individual atom is too small for you to see, so everything around you contains very many atoms.

An element is a substance that is made of only one sort of atom. Oxygen is an element because it only contains oxygen atoms. 

The atomic number: The number of protons.

Number of electrons: The same as the number of protons. 

Mass number: Total number of protons and neutrons.

Shells: 1st - 2 Electrons.

           2nd - Up to 8 electrons.

           3rd - Up to 8 electrons.

           4th - 1 or 2. 

The group number (Across the top&down): Shows the number of electrons in the outer shell.

The Periods (Across landscape): Show how many shells.

Group 1 (Alkali Metals):

• Their atoms all have just 1 electron in their outer shell.
• These elements burn in oxygen to produce solid metal oxides.
• They also react vigorously with water to produce hydrogen gas and metal hydroxides to dissolve to form alkaline solutions.

Group 0 (Nobel gases):

• They have a full outershell of electrons.
• Helium has 2 electrons in its outer shell.
• All of the others have 8 electrons in their outer shell.

Formins ions:

Metal and non-metals react together to form compounds. The compounds formed are called ions.

An ion is a charged particle formed when an atom or group of atoms, loses or gains electrons.

Forming molecules: 

Compounds formed from reactions between non-metals consist of molecules.

In a molecule, electrons are shared between atoms. 

These shared electrons make covalent bonds which hold the atoms in the molecule together.

Giving and taking electrons:

Metal atoms give electrons to non metals to form positive ions. 

Uses of limestone:  

As a raw material for making cement, mortar and concrete. 

As blocks and slabs for roads and pavements.

As small lumps in the base of roads and railways.

Building materials:

Limestone -> Heated with clay -> Forms cement 

-> Mix with sand for mortar.

-> Mix with sand and aggregate for concrete. 

(Water is also used).

Limestone is taken from the fround in quarries.

- New jobs are created from it

- It is vital for building materials.

But...

- It ruins the beauty of the countryside.

- Extra traffic. 

- Noise, visual and atomspheric pollution.

Thermal decomposition: 

Many metal carbonates break down when they are heated. 

Metal carbonate -> Metal oxide + Carbon dioxide.

When calcium carbonate is heated... it decomposes to form calcium oxide and carbon dioxide: 

CaCo3 -> CaO + CO2

Making an alkali:

Calcium oxide reacts vigorously with drops of water to make a white solid called calcium hydroxide. 

CaO + H20 -> Ca(OH)2 

A lot of heat is given out in the reaction. 

Calcium hydroxide is an alkali.

Limewater:

Limewater is a solution of calcium hydroxide in water. It is used to test for carbon dioxide. 

Carbon dioxide turns limewater cloudy. 

Calcium hydroxide + Carbon dioxide -> Calcium carbonate + Water.

Ca(OH)2 + CO2 -> CaCO3 + H2O

Unreactive metals such as gold are found in the earths crust.

Ores: 

Rocks contain metals or their compound. An ORE is a rock that contains enough of a metal to make its extraction economical. 

Rocks may contain too little metal to make extraction worthwhile. 

Over time, metal prices may rise and these low grade ores may become useful.

Iron is extracted from iron oxide in a blast furnace by reaction with carbon.

Other metals can be extracted like this if they are less reactive than carbon.

A reaction where oxygen is removed from a compound is called a reduction reaction.

Reactivity:

Most reactive metals are the most difficult and expensive to extract.

The least reactive are the easiest and cheapest to extract.

Smelting:

Copper is extracted from these ores by smelting. 

This involves heating copper orea in a furnace.

Traditioal mining and extraction methods have major environmental impacts. 

High grade copper ores are running out, so other extraction methods are being researched.

Electrolysis:

Copper is purified by electrolysis. 

Positive copper ions go to the NEGATIVE ELECTRODE. 

Negative copper ions go to the POSITIVE ELECTRODE.

Phytomining:

Metal compounds absorbed by roots -> Plant concentrates metal compounds in its shoots and leaves -> Plants are burned -> Ash contains metal compounds.

Bioleaching:

Copper can also be extracted by bioleaching.

Certain bacteria absorb metal compounds to produce a solution called leachate.

This has a high concentration of metal compounds. 

Scrap iron may be used to displace copper metal from these solutions. 

Extracting metals from their ores:

- Uses up limited resources from their ores.

- Uses a lot of energy.

- Damages the environment.  

Recycling metals:

- Metal ores will last longer.

- Less energy is needed to recycle metals. 

- Fewer quarries and mines needed. 

- Less noise and dust pollution.

- Less land needed for landfill sites.

Used metal items must be collected and transported to the recycling centre.

Different metals must be removed from used items and sorted.

Recycling saves different amounts of energy depending on the metal involved.

Cast iron:

Iron oxide is reduced to iron in a blast furnace. 

Iron straight from the blast furnace is about 96% pure.

The impurities it contains make the iron brittle and this limits its uses.

Blast furnace iron is used as cast iron.

Cast iron is strong and used in manhole covers and drain pipes ect. 

Steels:

• Most iron is converted to steel. 
• There are different types of steel but they are all alloys.
• Steels are mixtures of iron and carbon, often with other materials.

Low carbon steel is easily shaped.                    High carbon steel is hard.

Stainless steel us resistant to corrosion.

Good for making things that need to let heat or electricity pass through easily. 

They are good conductors of heat. 

The transition meta;s include iron, titanium and copper. 

They are good conductors of electricity.

Useful as structural materials.

They can be bent or hammered into shape. 

They are between groups 2 and 3.

Aluminium and titanium:

They are low density (Light weight).       Titanium is used int artificial hip joints.

Resistant to corrosion.                          Aluminium is used for aircraft parts.

Alkanes:

A hydrocarbon is a compound made up of hydrogen atoms and carbon atoms only. 

Most of the hydrocarbon molecules in crude oil are ALKANES.

Alkanes have the general formula Cn H2n+2. (Double the carbons and add 2).

An alkane molecule can be represented by its chemical formula or by its displayed structure. 

They are joined together by covalent bonds.

Mixtures:

The substance in a mixture are not chemically combined together. These substances can be: 

• Two or more elements.
• Two or more compounds.

Mixing does not change the chemical properties of each substance in a mixture.

Distillation is one of several physical methods that can be used to seperate the substances in a mixture. 

It is used to seperate a mixture of liquids that have dissolved into eachother.

The mixture is heated until on of the liquids evaporates. 

Its vapours are then cooled and condensed to form a seperate liquid.

Fractional distillation:

Fractional distillation is used to seperate mixtures contained several different substanced. 

It is used to seperate crude oil in to fractions in a continutous process.

Each fraction contains molecules with a similar number of carbon atoms and boiling point.

It happens in a fractionating column and the oil is heated to evaporate it this vapour rises up the column.

Each fraction condenses at different temperatures as it has different boiling points.

Complete combustion:

The combustion of hydrocarbon fuels releases energy to the surroundings. The hydrogen and carbon in the fuel reacts with the oxygen and is oxidised.

If there is plenty of oxygen, complete combustion occurs.

The hydrogen atoms in the fuel are oxidised to produce water vapour:

2H2 + O2 -> 2H2O

The carbon is oxidised to carbon dioxide:

C + O2 -> CO2

If there is not eneough oxygen, incomplete combustion (partial occurs). 

The hydrogen in the fuel is still oxidised to water vapour but the carbon is not fully oxidised.

These products are also formed: 

Carbon monoxide. and Particulates (Solid particles).

The solid particles contain soot which is carbon and unburnt fuel.

NOx are oxides of nitrogen such as NO and NO2. 

They are produced from nitrogen and oxygen in the air. 

They form at high temperatures like those found in furnaces and car engines.

NOx are also a cause of acid rain. 

Most fuels naturally contain some sulphur. 

When the fuel burns, the sulphur oxidises to sulphur dioxide gas: 

S + O2 -> SO2

Acid rain damages rocks, buildings, trees and aquatic life. 

Sulphur dioxide pollution can be reduced by: 

Removing sulphur from the fuel. 

Removing sulphur dioxide after burning.

Burning biofuels releases less carbon dioxide overall than burning fossil fuels.

Biodiesel and Bioethanol are biofuels.

- Biodiesel can be used in diesel emgines.

- Bioethanol can be mixed with pethrol and used in engines.

But...

- Farmland that could be used for food production is used for biofuel production instead.

Both fuels are produced from renewable resources. However, non-renewable resources may be used indirectly:

- To make fertilisers for the plant crops.

-To provide energy during their manufacture and transport.

Water vapour is the only product made when hydrogen burns:

2H2 + 02 -> 2H20

- No carbon dioxide is made when the hydrogen burns.

- Hydrogen can be made by passing electricity through water.

But... 

- Most hydrogen is produced from fossil fuels at the moment. 

- Electricty needed to make hydrogen from water may be generated by burning fossil fuels.

- Hydrogen is difficult to store and there are only a few places that sell it.

Cracking: 

Thermal decomposition reaction. 

Oil fractions are heated so they vapourise.

Their vapours are either ...

Passed over a hot catalyst or mixed with steam and heated to a very high temperature.

Alkenes:

Unsaturated hydrocarbons as they have double bonds. 

Cn H2n .(Amount of hydrogen = Double the amount of carbons.

Alkenes can be used to make polymers (Plastics).

Polymerisation:

Alkene molecules can act as monomers. 

They can join together in a polymerisation reaction to make very large molecules called polymers (Polyethene).

Polymers are used in .....

Babies nappies (Hydrogel).

Medical dressings.

False teeth and fillings.

A biodegradable material can be broken down by microbes. 

Cornstarch is a natural substance that microbes can break down. It is used for making biodegradable substances such a carrier bags.

-> But many polymers are not biodegradable. Microbes cannot break them downand they do not rot.

-> This is a useful property because items made from polymers last a long time and may be recycled. 

-> Polymers that are not biodegradable are difficult to dispose of - Sometimes they cause litter.

Landfill sites:

- Waste is disposed of quickly. 

- Waste is out of sight once it is covered over.

But... landfill space is running out, Most polymers are not biodegradable and will last many years.

Most crude oil is used for fuel, but it is also used to make chemicals.

These include medicines and paints as well as polymers.

Oil is a limited resource, It will run out one day if we keep using it.

Fermentation:

A natural process. It uses yeast to convert sugar from plants to ethonol: 

Sugar -> Ethanol + Carbon dioxide.

Fermentation is used to make alcohol or fuel.

Hydration of ethene:

Most ethanol for industrial use is made by hydration of ethene.

Ethene and steam react tigether in the presence of a catalyst to make ethanol.

Pressing and filtering:

The plant material must be crushed to release oil and water from the plant cells.

The oil floats on top of the water and crushed plants.

The crushed plant material may need pressing to remove the oil. 

The crushed plant material can be removed by filteration. 

The oil and water are separated to make a useful product.

Water is boiled to create steam.

Steam passed through the plant material.

The steam carries away the oil. 

The mixture of steam and oil is cooled 

Oil floats on the condensed steam.

Cooking with oil:

It cooks at high temperatures, quickly and has different flavours.

But...

Releases more energy when it is eaten.

Oils do not dissolve in water. If an oil and water are shaken together they form a mixture called an emulsion. 

Compared with oil or water alone, emulsions:

Are thicker (Viscous).

Have better coating ability (Stick to things better).

Have a better texture and appearance. 

This makes them useful for paints, salad dressings, ice cream and cosmetics.

An emulsion will eventually separate out again untilo all the oil is floating on the water. 

Emulsifiers are substances that make emulsions more stable and do not allow seperation. 

E.g. Egg yolk.

Emulsifier molecules:

They have 2 parts: Hydrophilic (Loving)  head and hydrophobic (Hating) tail. 

The head dissolves in water and the tail dissolves in oil. 

They surround droplets of oil or water, stopping them from joining up again. This works whether the emulsion is made of oil droplets in water, or water droplets in oil.

Unsaturated vegetable oils:

Have long chains of carbon atoms joined together:

Saturated vegetable oils only have carbon to carbon single bonds, C,C.

Unsaturated vegetable oils have some carbon to carbon double bonds C=C as well.

Polyunsatuated oils have lots of C=C bonds. Unsaturated oils are better for health than staturated oils and fats.

Testing for unsaturation:

Bromine water is orange. It turns colourless when it is mixed with an unsaturated substance. 

The C=C  bonds change to C-C bonds in the reaction. This means:

The more C=C bonds there are, the more bromine water can be added before it stops becoming colourless.

Unsaturated oils can be hardened. 

A nickel catalyst speeds up the reaction between hydrogen and the C=C bonds.

Hardened vegetable oils are described as hydrogenated. 

They are less unsaturated than the oils used to make them.

Hydrogenated oils have higher melting points than the origional oils, they are:

• Solid at room temperature.
• Used to make margarine.
• Useful in cakes and pastries.

The earth's crust and the upper part of the mantle are cracked into several very large pieces. These are called tectonic plates.

The tectonic plates move at a few cm per year. 

They move because of convection currents in the mantle. 

These currents are driven by heat from natural radioactive processes in the earth.

Shrinking earth: Before Wegener, scientists thought that features on the earths surface were caused by it shrinking. 

The idea was that as the earth cooled after it was formed, its crust shrank and wrinkled to form mountains. The idea is now disproved.

Prediction: If this theory is correct, then mountains should cover the earth. 

Obervation: Mountains are not everywhere.

Continental drift:  Alfred Wegener suggested that all the earth's land was once joined together forming a supercintinent. This broke up millions of years ago and the landmasses moved apart.

Wegner's ideas were based on an observation involving South America and Aftrica.

It has basically stayed the same for the last 200 million years.

The atmosphere:

The 2 main gases in the atmosphere are :

Nitrogen 4/5 - 78% 

Oxygen 1/5 - 21%

1% Other gases including argon, water vapour and carbon dioxide.

Raw materials:

Earth's atmosphere, crust and oceans are the only sources of the minerals and other resources needed by humans. 

Gases in the air can be used as raw materials for industrial processes. These gases have different boiling points, so they can be separated by fractional distillation:

Air is cooled to -200 degreese and liquefied.

Liquid air goes in to a fractionating column.

Nitrogen gas leaves at the top.

Liquid gas leaves at the bottom.

Nobel gases like argon are also sepparated.

Earth's early atomsphere =

Like venus and mars today: Mainly carbon dioxide with little or no oxygen 

+

Water vapour, small amounts of ammonia and methane.

Carbon dioxide levels: As the earth's atmosphere has developed: 

• Carbon dioxide levels have gone down.
• Oxygen levels have gone up.

Photosynthysis by plants and algae is one reason for these changes.

Fossil fuels:

Fossil fuels formed over millions of years from the remains of dead plants and animals. The carbon they contain origionally came from the atmosphere when the organisms were alive. 

Carbon dioxide was 'locked up' in fossil fuel as:

Carbon in coal.

Hydrocarbons in oil and gas.

Coal is a type of sedimentary rock.

Carbon dioxide is soluble in water. 

This is why carbon dioxide from the atmosphere dissolves in the oceans.

The oceans contain a lot of water so they act as a huge reservoir for carbon dioxide.

Carbon dioxide dissolves in water to form an acidic solution. 

When the ocean absorbs carbon dioxide, the pH of the water is reduced (Becomes more acidic). 

This affects the environment in the oceans.