C1 Revision Notes

Chemistry Core science revision notes C1 AQA

Atoms elements and compounds

All substances are made out of atoms. Compounds are different types of elements mixed together. These are held by chemical bonds. An atom has a nucleus with electrons around it.

Atomic structure

In the nucleus of an atom, there are protons and neutrons. Electrons orbit the nucleus. Any atoms have the same number of electrons as it has protons. Protons are positive. Neutrons are neutral. Electrons are negative. Because an atom contains equal numbers of electrons and

protons, the overall charge is zero. The number of protons in an atom is its atomic number. The elements in the periodic table are arranged in order of their

atomic number. If the atomic number is eight, then it will be the eighth element

listed. The mass number of an atom is protons plus neutrons. Number of neutrons = mass number – atomic number

The arrangement of electrons in atoms

Each shell represents a different energy level. The lowest energy shell is the one next to the nucleus. The first energy shell can only hold up to two electrons. The rest can hold up to 8.

Abdullah Ahmed™ All rights reserved®Copyright © 2011 – 2012


All the elements in group 1 have 1 electron. All the elements in group 2 have 2 electrons. This carries on and on, in this manner.

Group 0 or 8 are unreactive. These are called the noble gases.

Forming bonds

Some atoms react with each other by transferring electrons to form chemical bonds. This happens when metals react with non-metals.

When a metal bonds with a non-metal, the metal atom gives one or more atoms to the non-metal.

Both are charged atoms called ions. Therefore metal is then positive. Non-metal is negative. Opposite charges attract with each other, this forms strong bonds. This is called ionic bonding. This is called an ionic bond. However, non-metals reacts with each other in a different way.

They share their electrons by overlapping each other. This is called covalent bonding.

Limestone and its uses

Limestone is a rock mainly made out of Calcium carbonate. Powdered limestone can be heated with powdered clay to make

cement. When you mix cement with crushed rock, sand, and water you get

concrete. When limestone is heated strongly, you get calcium oxide. This is

called thermal decomposition. Carbon dioxide is also formed.

Reactions of carbonates

Buildings made out of limestone suffer from acid rain.



The limestone reaction cycle

Adding water to calcium oxide makes calcium hydroxide. Calcium hydroxide is an alkali. Farmers use it improve soil that is acidic. It is also used to neutralize acidic waste gasses.

Cement and concrete

Calcium hydroxide mixes with sand and water to produce mortar. Mortar holds building materials together. The more sand there is the weaker it is. Lime mortar does not harden quickly. It will not harden when in contact with water. Cement is made when limestone and clay are heated together. Water, cement and sand makes concrete. Rocks or aggregate is

also used. This is very strong.

Extracting metals

Oxygen is normally combined with these metals. Metals are found in the earth’s crust. The way you extract a metal depends on its reactivity series. A more reactive metal will displace a less reactive metal. Carbon is used to extract a metal. We must heat the metal with carbon. We call the removal of

oxygen reduction. Metals that are more reactive than carbon usually end with –ium.

These then have to be extracted by electrolysis. This is usually expensive.



Irons and steels An iron ore normally is combined with oxygen to form iron oxide. Iron from the ore normally has a lot of carbon in it. It also has other impurities. Pure iron is very brittle. We extract iron from a blast furnace. A metal that is mixed with other elements are called alloys. Steel is an alloy of iron. By adding the elements in controlled amounts, you can change

the property of steel. There are lots of different types of steel. Carbon steels are the simplest. You have to remove most of the carbon from it. These are the cheapest steels to make. These contain small amounts of carbon. Low alloy steels are more expensive because they contain more

metals. These are easily shaped. High alloy steels are more expensive and harder. These contain a much higher percentage of other metals. Stainless steels do not rust and have a great hardness and

strength. The more carbon there is in the steel, the harder it is, and more

expensive it is.

Aluminium and titanium

Aluminium and titanium have a low density and are very strong.

These do not corrode. Aluminium is a good conductor, and has many other uses.



Because aluminium is reactive than carbon, it has to be extracted by electrolysis.

This is a very expensive process. Titanium has a very high boiling point. Normally used for bikes and jet engines. Titanium is less reactive than carbon. Unfortunately, carbon

reacts with titanium, making it very brittle. This means sodium or magnesium has to be used. But these are first extracted by electrolysis.

These two metals are very expensive.

Extracting copper

Cooper ores are in danger of running out. There are 2 main ways in which copper is extracted. One way is to use sulphuric acid to produce copper sulphate

solution, before extracting the copper. The other process is smelting (roasting). You heat copper ore

very strongly in a furnace with air to produce copper. Care has to be taken to avoid sulphur dioxide to get into the

air. These methods are expensive, and use enormous amounts of

heat and energy. Metal ions are always positively charged. So in electrolysis,

they are attracted to the negative electrode. This pure's the copper from other elements.

Copper can also be extracted from copper sulphate solution, by adding scraps of iron. Iron is more reactive than copper so it can displace copper from its solutions.

We can now use bacteria to get copper from low grade ores.



We can now use a bacteria (bioleaching), and even plants (phytomining) to help extract copper.

In phytomining, plants absorb copper ions as they grow. Then the plants are burned, and the metals can be extracted from ash. This forms the solution copper sulphate. Then it can be purified by electrolysis or using scrap iron.

In bioleaching, bacteria feed on the low grade ores; by a combination of biological and chemical processes you can get a solution of copper ions called leachate. Once again you have to use electrolysis or use an iron scrap.

Useful metals

The transition metals can be bent into any shape, and are good conductors of electricity and energy.

Transition metals make them useful for building, and making things. Copper gold and aluminium are all alloyed to make them harder.

Fuels form crude oil

Crude oil is a dark and smelly liquid. It contains a mixture of two or more elements or compounds,

which are not chemically combined together. Nearly all of the compounds in crude oil contain a single bond

alkane. We call these hydrocarbons. These are saturated hydrocarbons. Their general formula is: CnH(2n + 2)



Fractional distillation

Some hydrocarbons are small and others are large. The short ones are the ones that are the most useful. The longer the chain, the higher the boiling point is. The longer the chain it takes longer for it to turn to gas. The longer the chain the thicker it is. The longer the chain the harder it is to burn. We separate crude oil into hydrocarbons with similar boiling

points. These then come out of the appropriate fraction. This is called fractional distillation. Crude oil is fed into the bottom of a fractionating column. The column is very hot near the bottom and cool near the top. Shorter chains come out form the top, and the longer chains

come out from the bottom. Then the alkanes come out of the appropriate column.

Burning fuels

Lighter fractions are very useful as fuels. When you burn hydrocarbons in plenty of air, carbon dioxide

and water are released. The carbon and hydrogen are oxidised completely. Oxidised means adding oxygen in a chemical reaction in which

oxides are formed. All fossil fuels produce carbon dioxide and water when they

burn in plenty of air. For an example: Propane + oxygen → carbon dioxide + water

C3H8 + 5O2 → 3CO2 + 4H2O



BUT these fuels also contain impurities such as sulphur. This then reacts with oxygen to produce sulphur oxide. This is

acidic and poisonous and is bad for the environment. It can also cause engine corrosion. However when we burn fuels in a place where there is NOT

ENOUGH oxygen such as a car engine, more pollution can be produced.

When there is not enough oxygen, we get incomplete combustion.

Instead of all the carbon turning into carbon dioxide, we also get carbon monoxide. This is very poisonous.

Your red blood cell can pick this up and carry it around your blood as oxygen.

The high temp. of a cars engine can also lead to nitrogen and oxygen reacting.

This produces nitrogen oxide. These are poisonous and can trigger some people’s asthma.

This can also lead to acid rain. Diesel engines burn much bigger chains of hydrocarbons, with

bigger molecules than petrol. When this burns it gets carried into the air. These are called

particulates. These are made out of carbon, and unburnt hydrocarbons.

These can cause cancer and can damage cells in our bodies.

Cleaner fuels

When we burn a fossil fuel, carbon dioxide is produced.



This then adds to the atmosphere, increasing carbon. This can cause global warming.

We can use catalytic converters. This reduces carbon monoxide and nitrogen oxides produced in the car engine.

These are expensive.

Alternative fuels

Biofuels are fuels made out of plant or animal products. This is much less harmful to plants and animals. More cleaner. We can also use ethanol. We can ferment the sugar from the

sugar cane to produce ethanol. You can then add it to petrol. The sugar absorbs the CO2 when burnt.

Cracking hydrocarbons

Some of the heavier fuels are not very useful. We can then break them down by cracking. This takes place in a cracker. It is heated and thermal

decomposition takes place. When we burn a hydrocarbon, we get other alkanes, but we

also get alkenes. Alkenes are unsaturated hydrocarbons. These contain double

bonds. To check of you have an alkane or an alkene you can use

bromine water.

Unsaturated hydrocarbon + bromine water → colourlessSaturated hydrocarbon + bromine water → no reaction

Making polymers from alkenes



We can use hydrocarbons to make a range of things. From cosmetics to explosives. The most important way is to produce plastics.

Plastics are made out of huge molecules made out of small molecules called monomers.

A lot of monomers joined together are called polymers. Ethane can be a monomer. We can then join these up, and

then this is then called poly (ethene). This can be used for plastic bags and plastic bottles.

When the alkene molecules join up together the double bond they have opens up and is replaced by a single bond. This is called polymerisation.

New and useful polymers

There are light sensitive polymers, hydrogels, shape memory polymers.

Plastic waste

Scientists are working on biodegradable plastics. Microorganisms can break them down.

Plastics will cause crops to get expensive. We can now recycle plastics.

Ethanol Ethanol is one of the members of the alcohols. It is the one that is found in alcoholic drinks.



It is made by fermentation of sugar from plants. Enzymes in the yeast break down the sugar into ethanol. Carbon dioxide gas is also given off.

Sugar (glucose) → [yeast] ethanol + carbon dioxide Ethanol is also a solvent. Ethanol for fuel or for any other industrial use can be made

from ethene instead of fermentation. Ethene + steam → [catalyst] ethanol This reaction is called hydration. This reaction is also reversible. It produces no waste products.

Extracting vegetable oils

Plants use the suns energy to produce glucose from carbon dioxide.

Carbon dioxide + water→ glucose + oxygen. Plants then turn this glucose into other chemicals such as

vegetable oils. We find these oils inside the seeds of a rape plant. We can then crush the seeds to produce oil. The impurities are

removed to make it useful. We extract other vegetable oils by steam. We can extract

lavender plants by distillation. The plants are placed into water, and then boiled. The oil and

the water evaporate, to give pure lavender oil. Vegetable oils are very important foods. They provide nutrients. They are a source of vitamin E All vegetable oils have chains of carbon atoms.



The double bonds carbons are healthier because they are unsaturated hydrocarbons. We call these unsaturated oils.

We can detect them using bromine water.

Cooking with vegetable oils

When cooking food, we heat them to a temp. where chemical reactions cause permanent changes.

When using vegetable oils, the food cooks quickly. Often the outside changes colour, and turns crispier. Inside the food should be softer, so you shouldn’t cook for that long.

No chemical bonds are broken when vegetable oils melt or boil. These are physical changes. Not chemical.

Unsaturated vegetable oils are liquid at room temperature. The boiling and melting point can be increased by adding

hydrogen to the molecules. This reaction replaces some or all of the double bonds with

single bonds. With higher melting point, the liquid becomes solid at room

temperature. This process is called hardening. We do this by reacting it with hydrogen (H2). To do this process, we must use a nickel catalyst at around

60oC. When hardening, a chemical change takes place. This is normally used for margarines, cakes, biscuits, and the

like.

Emulsions

Oil and water do not mix. Obviously.



However if you add oil in small amounts, the oil spreads out. This mixture is called an emulsion. Milk is just water and small amounts of animal fat dispersed.

A substance that stops oil and water separating is called an emulsifier.

This means that the emulsion is thick and smooth due to an emulsifier.

An emulsifier is a molecule with a tail that is attracted to oil, and head that is attracted to water. The tail is hydrophobic, and carries a charge. While the head is hydrophilic.

Food issues

Additives are substances that preserve food; make it look better, make it to taste better, and to improve its appearance.

In Europe, they are known as E numbers. Emulsifiers make a food less obvious that it contains a lot of fat. Vegetable oils reduce chances of heart disease.

Structure of the earth

The earth has a dense core, surrounded by mantle. Outside the mantle you will find the crust.

Above the earth’s crust there is a thin layer of gases surrounding the earth. This is the atmosphere.

Outer core is liquid, while the inner core is solid. We get all the natural resources and materials from the crust,

oceans, and atmosphere.

The restless earth



The continents move a few cm a year. The earth’s crust is broken into tectonic plates. Deep within the earth, radioactive atoms decay, producing vast

amounts of energy. This heats up molten minerals in the mantle which expand. This rises towards the surface. Cooler material sinks to take its place. This process is cause by convection currents.

Where the edge of the plates meet, huge stress builds up and causes earthquakes.

Earthquakes and volcanoes happen where tectonic plates meet.

The earth’s atmosphere in the past

Scientists think that the earth was formed 4.5 billion years ago. Volcanoes released carbon dioxide, water vapour, and

nitrogen gas. As plants spread, it increased the level of oxygen in the

atmosphere.

Life on earth

One theory states that the compounds needed for life came from reactions involving hydrocarbons, such as methane and ammonia. The energy provided for the reaction, could have been lightning.

All the theories explaining how life started on earth are unproven. This is because they talk bull shit.

The only thing is to believe in Islam.

Gases in the atmosphere



Carbon dioxide, in early earth had a lot. Now it is just 0.4%. The carbon ends up in new plants material during

photosynthesis. The animals then eat the plants and then the energy is

transferred into the animal’s teeth, bones, skin and so on. Over millions of years, the dead bodies are ended up in the

bottom of oceans. They then form sedimentary carbonates rocks like calcium carbonate. Some of these living things form into fossil fuels by the movements of the earth heated within the crust. The carbon is then locked up into these living things.

At the same time ammonia and methane reacted with oxygen formed by plants.

This got rid of ammonia and methane. Fractional distillation is the process in which liquids with

different boiling points are separated. The first step to separate the gases in the air is to turn it get air

cold enough for it to condense into a liquid. It has to be cooled to a temperature of -200oC.

In industry, they do this by compressing the air about 150 times.

It is then boiled into different boiling points until the gases enter the appropriate fraction.

Carbon dioxide in the atmosphere

Levels of carbon dioxide in the atmosphere are increasing. This is mainly due to fossil fuels.





WARNING: This document is copyrighted. Any copiers will face prosecution. All rights reserved Abdullah Ahmed™


Documents

C1 Revision Notes