Revision Notes Materials, Substances and Chemicals

All matter is made up of small particles called atoms.

There are approximately 100 different elements and each of these is listed in the Periodic Table.

Each element is made up of one type of atom.

Each element is made up of the three following sub-atomic particles

· protons – found in the nucleus and have a positive charge

· neutrons – also found in the nucleus and have no charge

· electrons – orbit the nucleus and are negatively charged

The number of subatomic particles in each atom can be calculated using the two numbers associated with the symbol in the periodic table.

The smaller of the two numbers (usually the lower number) is the Atomic Number; this tells you the number of protons in an atom and the number of electrons in the atom.

The larger of the two numbers (usually the top number) is the Atomic Mass. This is the total number of protons and neutrons in the nucleus.

For the above sodium atom Na the subatomic particles are as follows

· 11 protons

· 11 electrons

· 12 neutrons

Electrons orbit the nucleus in different shells. Shell 1 is nearest the nucleus, then shell 2 and shell3 etc.

The first shell can hold a maximum of 2 electrons

The second shell can hold a maximum of 8 electrons

The third shell can hold a maximum of 8 electrons

The lowered numbered shells must be filled first, therefore for the above sodium atom it will have

· 2 electrons in shell 1

· 8 electrons in shell 2

· 1 electron in shell 3

An element is something that cannot be split up into anything simpler (e.g.: oxygen, hydrogen, iron and the rest of the periodic table)

A mixture contains two or more substances that are not chemically combined (the air is a mixture of gases).

A compound is a pure substance that contains two or more elements that are chemically combined (e.g.: CO₂, H₂O)

Compounds are represented using formulae; these contain the symbols of the elements present and the number of each element present.

NaCl – sodium chloride contains 1 sodium atom chemically joined to 1 chlorine atom.

NH₃ – ammonia contains 1 nitrogen atom chemically joined to 3 hydrogen atoms.

CaCO₃ – calcium carbonate contains 1 calcium atom, 1 carbon atom and 3 oxygen atoms chemically joined together.

The changes that occur during reactions are represented using equations, these represent the rearrangement that occurs during reaction and the number of each atom must be the same on either side of the arrow.

For example

2H₂ + O₂ 2H₂O

4 x H 4 x H

2 x O 2 x O

Numbers can only be put before the elements or compounds, the formulae can not be changed.

The materials we use in our lives

All the materials we use were once part of the Earth’s crust.

Materials removed from the crust can be either

· found in an uncombined state e.g.: gold, sulphur

· found in a combined state e.g.: iron and aluminium

Materials that are found in an uncombined state (i.e. as elements) tend to be fairly unreactive, whereas those that are found in a combined state tend to be reactive elements.

Calcium carbonate is removed from the ground as a compound, it occurs as limestone (sedimentary rock) or marble (metamorphic rock).

Uses for limestone

· extraction of iron

· building

· making cement

Uses for marble

· decoration

Useful mixtures from the Earth

Two important mixtures that are extracted from the Earth are crude oil and rock salt.

Rock salt is a mixture of sodium chloride and rock; it has limited use in its unpurified

state. It can be purified by adding the impure form to water, the salt dissolves and the insoluble rock can be filtered out. The remaining solution can be evaporated to leave pure sodium chloride.

Sodium chloride is used in the food industry and as a raw material for the production of chlorine.

Crude oil is a mixture of several different organic compounds. The individual compounds that make up crude oil all have different boiling points. The mixture is separated by

fractional distillation. The mixture is heated to over 300^oC, at this temperature all of the fractions with the exception of one are converted to gases. The mixture of gases rises up a column where the temperature is gradually decreased. At its boiling point each gas condenses and is drained away. Fractions with a very low boiling point exit through the top of the column.

Fractions obtained from crude oil include

· liquefied petroleum gases – used as a fuel (LPG)

· petrol – most commonly used fuel for cars

· diesel – fuel used for lorries, buses, trains & cars etc

· kerosene – used a fuel for aviation industry

Paraffin, propane and butane are also obtained from crude oil.

Fossil fuels

Oil, coal and gas are the three fossil fuels. They have been made over millions of years from animal and plant life. Living material (or once living) contains the element carbon and is known as organic material. Material from things that have not lived is known as inorganic material.

Fossil fuels are the basic raw material for making many of the materials we depend on

· petroleum products (see above)

· polymers and plastics

· pharmaceutical products

Extracting metals from their ores

Most of the metals that we depend on are found within ores in the ground. For example iron occurs in the ground in its ore (iron oxide – haematite)

aluminium occurs in the ground as its ore (aluminium oxide – bauxite)

An ore is a mixture of a mineral surrounded by rock. many ores contain the metal in the form of oxides e.g.: Al₂O3 & Fe₂O₃.

Metals that are less reactive than carbon (refer to reactivity series) can be isolated by being reacted with carbon. The carbon removes the oxygen from the metal, this is called reduction.

Lead can be obtained by reacting lead oxide with carbon.

lead oxide + carbon lead + carbon monoxide

The lead has lost an oxygen and therefore been reduced.

The carbon has gained oxygen and has therefore been oxidised.

Extraction of iron

Iron is extracted from its ore (haematite) in a blast furnace. The following materials are used for the process

· haematite

· coke (carbon)

· hot air

· limestone

A temperature above 1000^oC is required.

carbon + oxygen carbon dioxide

C + O₂ CO₂

carbon dioxide + carbon carbon monoxide

CO₂ + C 2CO

iron oxide + carbon monoxide carbon dioxide + iron

Fe₂O₃ + 3CO 3CO₂ + 2Fe

Colloids

Many of the materials we use consist of one substance finely mixed with another; the substances in the mixture can be solid, liquid or gases.

Colloid	Disperse/continuous phase	Examples
solution	Transparent solution of a solid dispersed in a liquid	Tea without milk, sugar in water
suspension	Cloudy mixture of a solid dispersed in a liquid	Milk of magnesia, toothpaste
gel	Jelly like mixture of a solid dispersed in a liquid	Hair gel, jelly
emulsion	Cloudy mixture containing tiny droplets of one liquid dispersed in another	Paint, milk, cream, mayonnaise, salad cream
foam	Bubbles of gas dispersed in a liquid	Whipped cream, froth on a glass of beer, washing lather, shaving foam
aerosol	Droplets of a liquid dispersed in a gas	Spray deodorant, hair spray
foa foam	Bubbles of a gas dispersed in a solid	Sponge cake, foam rubber, clay soil

Inorganic/Organic Chemistry

Due to the vast amount of chemicals known to man, chemists have categorized all materials as being either inorganic or organic.

Inorganic compounds are mainly non-living things such as rocks and minerals or the air. They are made of elements other than carbon (carbonates are the exception). There are many examples but some of the important ones include

· metals

· glass

· ceramics

· sulphuric acid

· nitric acid

· ammonia

The inorganic compounds that you need to be familiar with are given in the table below; you need to be familiar with the names and formulae.

compound	formula	compound	formula
ammonia	NH3	barium chloride	BaCl2
carbon dioxide	CO2	sodium chloride	NaCl
water	H2O	calcium carbonate	CaCO3
hydrochloric acid	HCl	copper carbonate	CuCO3
sulfuric acid	H2SO4	sodium carbonate	Na2CO3
calcium oxide	CaO	potassium nitrate	KNO3
iron oxide	Fe2O3	silver nitrate	AgNO3
lead oxide	PbO	barium sulfate	BaSO4
sodium hydroxide	NaOH	copper sulfate	CuSO4

Organic compounds mainly come from living things and they all contain carbon. Examples include

_· methane CH₄

· ethane C₂H₆

· propane C₃H₈

· butane C₄H₁₀

· ethene C₂H₄

· propene C₃H₆

· benzene C₆H₆

· ethanol C₂H₅OH

· ethanoic acid C₂H₅COOH

· propanone CH₃COCH₃

· methanal HCHO

· Carbamide (urea) (NH₂)₂CO

Fine and Bulk Chemicals

Chemical compounds are produced to satisfy the needs of society. Many materials are required in vast amounts, these are called Bulk chemicals. Ammonia, sulphuric acid and polythene are examples of bulk chemicals as are fertilisers which have increased in production as the population of the World has increased.

Those chemicals that are required on a much smaller scale are called fine (or speciality) chemicals. Examples of fine chemicals include medicines, dyes and pigments.

Endo and Exothermic Reactions

Chemical reactions can be used to produce energy in different forms; all of the following can be produced

· heat

· light

· sound

· electricity

An exothermic reaction is one in which energy is released to the surroundings, usually in the form of heat.

An endothermic reaction is one where energy is taken in from the surroundings (it has absorbed heat from its surroundings.

The temperature of reaction mixtures can be monitored to see if the reaction is endothermic or exothermic.

Most reactions involve the initial breaking of bonds in the reactant molecules and the reforming of bonds in the molecules of the product. The breaking of bonds requires an input of energy (i.e endothermic), the making of bonds releases energy (i.e exothermic). If the breaking of the bonds requires a greater energy input than the energy released when new bonds are made then the reaction will be endothermic.

Reactions where the energy released during the making of bonds is greater than the energy required to break the bonds are exothermic. They release energy and the surroundings become warmer.

for endothermic reactions ∆H is positive

for exothermic reactions ∆H is negative

These changes are represented in reaction pathway energy level diagrams.

All combustion reactions are exothermic, the energy released can be measured using a copper calorimeter and recording the temperature change for a fixed volume of water and a known mass of fuel.

Bonding

Materials bond in one of two ways, either covalently or ionically. Both forms of bonding occur in order for atoms to gain full outer shells.

Covalent boding occurs when atoms share electrons, examples of covalently bonded compounds are hydrogen chloride and water.

Ionic bonding involves the transfer of electrons from one atom to another, this causes the formation of charged ions. Examples of ionic bonding are magnesium oxide and sodium chloride.

Both types of bonding are represented using dot and cross diagrams.