Section 2 f) Summary

Metals can be placed in an order of most to least reactive, called the reactivity series.

This can be remembered using an acronym:
Please
Stop
Calling
Me
A
Cranky
Zebra
I
Teach
Lions
How
Cars
Save
Gold
Printers

More reactive metals will displace less reactive ones in a compound (e.g. a metal salt or a metal oxide), which can be demonstrated by dissolving the compound in water to make it aqueous, then adding another metal to see if it reacts; if it does, then it is more reactive. If it doesn't, it's less reactive.
Reactivity series can also be determined by evaluating the intensity of reaction with water or acid.

Sacrificial protection
Iron is a useful metal, and it's on the less reactive side. But, when exposed to water and air, it will rust. It can be protected using grease, oil, paint or plastic, but another method is galvanising.
Galvanising is a form of sacrificial protection, wherein the iron is coated in a layer of zinc, which is a more reactive metal. This causes the oxygen and water to react with the zinc instead of the iron, protecting it. This method can be employed in different metals, but is called sacrificial protection and not galvanising in this case.

Section 2 d) Summary

The Earth's atmosphere is made up of many different gases, including

• Nitrogen (78%)
• Oxygen (21%)
• Argon (0.9%)
• Carbon dioxide, Water vapour, etc. (>0.1%)

The last category includes greenhouse gases: Gases that trap the sun's energy inside the atmosphere, causing the greenhouse effect. This is usually a good thing; the greenhouse effect keeps us alive. But excess greenhouse gases are being released into the atmosphere, increasing the volume constantly (due to burning fossil fuels, etc.). This causes the enhanced greenhouse effect, where too much of the sun's energy is trapped and causes a heating effect called climate change. This is a dangerous process that is threatening the world we live in, and must be stopped. 

We can work out the percentage volume of oxygen in air with a simple experiment. 

1. Place a tube containing copper in the middle of two gas syringes (containing a known volume of air), attached so the ends are sealed. 
2. Gently heat the copper with a bunsen burner, while slowly pressing the syringes, alternating, and keeping an eye on the volume. 
3. Once the volume stops changing when you press the syringe through, turn off the bunsen burner and wait for it to cool. 
4. Compare the volume you started with, and the volume you ended up with, and calculate the percentage. This is how much oxygen was in there. 

Oxides can be formed by burning elements, for example:

• Burning magnesium forms magnesium oxide, a basic compound
• Burning sulphur forms sulphur dioxide, an acidic compound that can be dissolved to form sulphuric acid
• Burning carbon to form carbon dioxide, an acidic compound which has many uses but also contributes greatly to the enhanced greenhouse effect. 

Carbon dioxide is water-soluble, making it useful for carbonating drinks. The carbon dioxide is dissolved under high pressure, but as this is a reversible reaction when the pressure is released bubbles form.
It is also denser than air, making it useful for smothering fires. CO2 is used in many fire extinguishers for this reason.

Carbon dioxide can be formed by reacting hydrochloric acid and calcium carbonate:
Hydrochloric acid + Calcium carbonate --> Carbon dioxide + Calcium chloride + Water

HCl(aq) + CaCO3(s) --> CO2(g) +CaCl2(s) + H2O(l)

Calcium carbonate could be used as marble or limestone, and dropped into a sealed flask of dilute hydrochloric acid in small pieces. A delivery tube could be placed in the end of the bung to allow for the gas to be collected in the downwards displacement method.

Carbon dioxide can also be formed through the thermal decomposition of a metal carbonate, for example:
Copper (II) Carbonate --> Carbon Dioxide + Copper Oxide
CuCO3 --> CO2 + CuO

Another decomposition reaction is hydrogen peroxide heated with manganese (IV) oxide.
Hydrogen peroxide --> Water + Oxygen

Section 2 c) Summary

The group 7 elements, also known as halogens, are F, fluorine, Cl, chlorine, Br, bromine, I, iodine, and At, astatine. They all have antimicrobial properties, but in larger doses are toxic.

F - Fluorine - a pale yellow gas
Cl - Chlorine - a green gas
Br - Bromine - an orange liquid
I - Iodine - a purple solid
At - Astatine - a black solid

The halogens are in the same group, so have similar properties that show trends. As you go down the group, the elements get darker in colour, less reactive, and have a higher melting and boiling point.
The reason for this is because as the molecules increase in size, the distance between the valence electrons and the nucleus increases, weakening the forces of attraction and making it more difficult for the atom to attract another electron. Additionally, the increase in molecule size means the attraction between the molecules is more difficult to break, causing the increase in melting and boiling point.

This topic focuses primarily on fluorine, chlorine and bromine. Their reactivity series can be determined by combining a metal halide and aqueous halide, and seeing if a reaction takes place. By adding methylbenzene, we can see which molecules are present (purple is iodine, yellow is bromine)

This shows that chlorine is the most reactive of the three, and iodine the least. These are displacement reactions, where the less reactive halogen is replaced by the more reactive halogen. The more reactive one is reduced, it gains electrons, and the less reactive one is oxidised, it loses electrons.

Reactions 

 The hydrogen halides formed in reaction with hydrogen can be bubbled through water, which is a polar substance. This causes the molecules to dissociate, and the H+ and halide- ions split, the H+ ions being acidic. This creates an acid, e.g. hydrochloric acid with chlorine, hydrobromic acid with bromine. This only works because water is a polar substance; it has charged ends. Non-polar substances, such as methylbenzene will not cause the compound to dissociate as the charge is evenly distributed.

Section 2 c) Key Words

Displacement reaction: A reaction in which a less reactive molecule is replaced with a more reactive molecule.

Dissociation: the splitting of a molecule into smaller molecules, atoms, or ions, especially by a reversible process

Group 7: The seventh group of the periodic table. Elements in this group have 7 valence electrons and are known as halogens. They share similar properties due to their similar electronic configurations.

Halogen: A group 7 element. Examples include chlorine and bromine.

Non-polar: A substance in which the electrons are shared equally between the nuclei, resulting in an even distribution of charge.

Oxidation: Loss of electrons

Polar: A substance in which the molecules are arranged so one end has a positive charge and on has a negative charge.

Reactivity series: The order of reactivity

Redox Reaction: A reaction in which electron(s) are transferred from one molecule to another. The molecule losing an electron is oxidised, and the one gaining is reduced.

Reduction: Gain of electrons

Section 2 b) Summary

The elements of group 1 are:

• Li, Lithium
• Na, Sodium
• K, Potassium
• Rb, Rubidium
• Cs, Caesium
• Fr, Francium

They each have 1 valence electron, making them quite reactive. As you go down the group, from lithium to francium, the reactivity increases. This is because the number of shells of electrons increases, making the distance from nucleus to valence electrons further and decreasing the strength of the forces of electrostatic attraction. Because of these weaker forces, the atoms are able to lose their valence electrons more easily, making them more reactive. 

Group 1 elements react quickly and vigorously with cold water, indicating just how reactive they are. They must be stored under oil so they are unable to react with water or air while in storage. 

Reactions with cold water:

Lithium floats on the surface of the water due to its low density, gently fizzing and giving off hydrogen. It gradually reacts, forming an ionic compound that dissolves in water to form a lithium hydroxide solution. 

Sodium, like lithium, floats on the surface of the water. The heat from the reaction is enough to melt it, so as it moves around it forms a sphere, gradually decreasing in size. A white trail of sodium hydroxide follows this ball as it moves (due to hydrogen production propelling it), then dissolves to form a sodium hydroxide solution. It lets of yellow sparks as it reacts. 

Potassium reacts more violently than both elements before it. The reaction is faster, and the hydrogen produced is caught fire to, burning with a purple flame due to potassium contamination. Its product, potassium hydroxide, also dissolves. 

Rubidium, Caesium and Francium all react too violently to be demonstrated in a school, so this video shows how they (and the other ones too, with inaccuracy about francium which is unable to be obtained to react with water) react. 

Interesting (but unnecessary) information on Francium here (Francium is less reaction than caesium?)

Section 2 a) Summary

This is the most widely recognised version of the Periodic Table of Elements. At IGCSE level, the transition metals are not really relevant, so we look at a version like this:

The main difference is just that the middle groups are not counted, making it easier to recognise which group each element falls into. The Periodic table is organised based on the properties of the elements. A line can be drawn from between boron and aluminium to between polonium and astatine to separate metals and non-metals. The left side, and the majority of the table, is classified as metals. The right is non-metals.
Metals are characterised by:

• Basic (Alkali) hydroxides
• Electrical and heat conductivity
• Giant metallic structure/metallic bonds
• Ability to form cations

Non-metals are characterised by:

• Acidic hydroxides
• Insulating properties (except carbon)
• Covalent bonding
• Ability to form anions

Group 1 - Alkali metals
The first group is the alkali metals. They each have 1 valence electron. Reactivity increases as the periods increase, because the outer shells increase in distance for the nucleus and the forces of attraction weaken, so the element is able to lose this electron more easily.

Alkali metals react with cold water, an indication that they are extremely reactive.
Lithium, Li: Vigorous reaction, gives off bubbles of hydrogen gas, floats on the surface until the product created dissolves.
Sodium, Na: Faster, more vigorous reaction than lithium, melts into a sphere and lets off some yellow sparks.
Potassium, K: Violent reaction, creates a purple flame and pops with the force of hydrogen production.
The larger elements; Rb, Cs and Fr react so violently that it is unsafe to have in a school - they combust and create large explosions.
They also decrease in melting and boiling points as the atoms increase in size.

Group 7 - Halogens
Halogens are the seventh group of elements. They are non-metals that exist naturally as diatomic molecules. They each have 7 valence electrons; one short of a full outer shell. They all have antimicrobial properties in small quantities, but in large doses they are extremely toxic.

Halogens react with iron wool:

And with hydrogen gas:

As they become larger (descend down the periods?), Halogens become less reactive, darker in colour, more dense, and have a higher melting and boiling point.


Group 0 - Noble gases
Noble gases are the last group of the periodic table. Each of the elements has a full outer shell of electrons, so they are inert. Noble gases are the only elements that can form stable single-atom molecules at room temperature and pressure.
Noble gases include: Helium, neon, argon, krypton, xenon and radon.

Section 1 i) Summary

Electrolysis is defined as chemical decomposition produced by passing an electric current through a liquid or solution containing ions. This process by which we can obtain the individual elements from an ionic compound has truly revolutionised the world.

Ionic compounds do not conduct electricity while solid. This is because the ions are not free to move. When aqueous, the ions are dissociated and therefore are able to move freely. When molten, the bonds between the ions are broken and they are able to move freely. Electricity is able to pass through because there are free-moving charged particles that can carry current.
Ionic compounds have very high melting points, and because of this the solid is often dissolved in water to create an aqueous electrolyte. When molten ionic compounds are electrolysed, the rules are simple: Metal goes to the cathode, Non-metal to the anode. But with aqueous solutions, it is less simple.

At the anode: If the non-metal is a halogen, it will form at the anode. If it is not, hydrogen gas will form: 2H+ + 2e- --> H2

At the cathode: If the metal is a low reactivity metal, it will coat the cathode. If it is a high reactivity metal, oxygen gas will form: 4OH- --> O2 + 4H2O + 4e-


The amount of a substance removed can be calculated by how much charge has passed through.
1 mole of electrons is equal to 1 faraday, which is 96500 coulombs.
First, you have to know the ionic half equation, the current passing through, and the time it takes.
Then, you can calculate the charge with this equation:
Charge (in coulombs) = Current (in amps) x Time (in seconds)
Q = I T
Divide the charge you have just calculated by 96500 to get the number of faradays, which is how many moles of electrons transferred.
Then look at the equation to see how many moles of electrons there are for each mole of the product, and divide accordingly.
If you are trying to find the mass, multiply by Mr, and you will have mass in grams
If you are trying to find the gas volume, multiply by 24000 to get volume in cm3.
See examples in the specification here

Industry
One of the most common industrial uses of electrolysis is the electrolysis of brine, or sodium chloride. This is called chlor-alkali industry.

The products of this reaction are used for many different things:

Chlorine: killing bacteria, making bleach, making hydrochloric acid, etc.

Hydrogen: used in making ammonia, making margarine, etc.

Sodium hydroxide: Making soap, paper, ceramics, etc.

The ionic half-equations are:

2Cl- --> Cl2 + 2e-

2H+ + 2e- --> H2

Because two gases are formed, a diaphragm is put in place between the two electrodes to prevent them from mixing and reacting.

Section 1 h) Summary

When metals bond, they form a giant metallic structure, also known as a metallic crystal. They are made up of positively charged nuclei surrounded by a delocalised electrons, sometimes referred to as a 'sea of free electrons'. These free electrons allow metals to conduct electricity, as they are able to move and carry charge freely. 

This structure is a giant structure, meaning it is constantly repeating regularly. It is in sort of layers which mean that when force is applied, the ions will slide, and the metal will bend, not break. 

The strong forces of attraction between the electrons and charged metal ions are difficult to break; they require a lot of energy. This means that metals have high melting and boiling points. 

Metals are also:

• Shiny/lustrous: The giant structure means it has flat, smooth surfaces that reflect light.
• Hard: The giant structure is densely packed and difficult to dent
• High density: The ions are packed closely together, only tiny electrons keeping them apart
• Strong: The giant structure is difficult to break 

Section 1 g) Summary

Covalent bonding is the bonding of two non-metal atoms. It involves a shared pair of electrons. The attraction between the nucleus of each of the atoms and the electrons of the other atom creates a very strong covalent bond.

Simple covalent structures usually have low melting and boiling points, and are often fluid at room temperature, because the forces between the molecules are weak and don't require much energy to break. They have weak intermolecular forces.
Examples include: water, oxygen, carbon dioxide, hydrogen chloride, etc.

Giant covalent structures have very high melting and boiling points, because they have so many strong covalent bonds holding the atoms together. It requires a lot of energy to break that many covalent bonds, so they have high melting points.
Examples include: diamond (carbon), graphite (carbon), silicon dioxide, etc.

Dot and cross diagrams can be used to represent covalent bonding. Here are the most important ones for this topic:

Methane

Water

Hydrogen Chloride

Chlorine

Hydrogen

Ammonia

Oxygen

Nitrogen

Carbon Dioxide

Ethane

Ethene

Section 1 f) Summary

Ionic compounds are formed when a metal and non-metal meet, and there is a transfer of electrons. This causes both atoms to become oppositely charged ions, which experience strong forces of electrostatic attraction towards each other.

Ionic compounds are not easily broken apart, their strong forces of attraction mean they have high melting and boiling points: they require a lot of energy to break the bonds.
The compounds, as a solid, form a giant ionic lattice structure. It is a lattice, meaning it is regular which results in the solids forming into translucent, geometric crystals (think of salt).

This can be represented at a molecular level using the following diagram:

The positive and negative ions alternate, because like attractions repel and opposites attract. Therefore, when force is applied to an ionic solid, it breaks easily: it is brittle. This is because when the ions are forced to move, they don't slide over each other easily, they get close to a similar charge, causing a force of repulsion and making it break apart easily.

It is important to know the charges of ions seen commonly in this topic. We can deduce the charge based on the number of outer shell (valence) electrons (if it has two, it will lose them, if it has six, it will gain two, etc.)
The following periodic table is a useful guide on the trends:

Section 1 e) Summary

This topic is about chemical formulae and equations, how to write and balance them correctly, as well as how to calculate reacting masses.

In a chemical reaction, the number and types of particles should be the same on both sides. But as different molecules require different numbers of each element, the ratio of each molecule created is relative. We must balance the equation to ensure the number of particles, for example:

H2 + O2 --> H2O
The above equation is unbalanced. There are two particles of hydrogen, and two particles of oxygen on the reactants side, but on the products side there are two particles of hydrogen and only one particle of oxygen.
We can remedy this by first changing the particle with the deficit:
H2 + O2 --> 2H2O
Now there are two oxygen particles on either side of the equation. But there are also double the number of hydrogen particles in the products than in the reactants, but this is easily fixed:
2H2 +O2 --> 2H2O
Now there are 4 hydrogen and 2 oxygen on both sides of the equation: it is balanced.

We can use balanced chemical equations to figure out the reacting masses, as it gives us a ratio of the moles, which when multiplied by Mr gives the mass, as shown in this formula triangle:

For example, if we have this balanced equation:

Fe2O3 + 3CO --> 2Fe + 3CO2

And we are told that there is 75 grams of iron oxide, and that we have to calculate what mass of iron can be derived from this with excess carbon monoxide, it can be calculated as follows:

Mr of Iron Oxide: 160

Mass of Iron Oxide: 75 g

75 / 160 = 15/32 mol

Ratio of Fe2O3 : Fe is 1:2

15/32 x 2 = 15/16 mol

Mr of Fe: 56 

56 x 15/16 = 52.5g

52.5 grams of iron can be derived from this reaction 

However, the actual iron we get from this reaction in reality is lower. This is because some may be lost in separation etc., this is called the yield. 

Percentage yield is how much is actually collected of the amount that is expected, and can be calculated with the following equation:

Yield = (mass of product collected x 100) / mass of product calculated

This tells us what percentage of the product is lost in this method, and can be used to compare different methods, as well as give a more accurate prediction of what the actual yield will be. 

For this topic, it is important to know the specifics of two different reactions, which simply demonstrate that you know how to calculate reacting masses and percentage yield:

Metal Oxide
Weigh a crucible with its lid, then place magnesium inside and weigh again, recording the measurements.
Heat it strongly over a roaring bunsen flame, and gently open the lid with tongs momentarily, to allow oxygen to get in without letting the magnesium oxide escape.
Weigh it every so often so you can see how the mass is changing. When the mass stops changing, the reaction is complete.
Record the final mass of the magnesium oxide and crucible, and use the numbers you recorded earlier to determine the mass of magnesium and the mass of oxygen.
Using each element's relative atomic mass, the empirical formula can be determined.

Salt (crystallisation)
Weigh an evaporating basin, then add hydrated copper sulfate and weigh again.
Heat the solution over a bunsen burner, gently stirring to ensure even heating.
Stir until the solution loses colour, indicating all water has been lost.
Weigh again to find the mass of water lost, and also the mass of anhydrous copper sulfate.
Divide mass by Mr of the copper sulfate, and do the same with water.
Simplify this to find the ratio of water to copper sulfate, and round to the nearest whole number,
e.g. CuSO4 ● 5H2O

Section 1 d) Summary

Relative atomic mass (Ar) is the mass of an atom, relative to Carbon, which has an Ar of 12. This is because of the tiny size of atoms, measuring in fractions of a gram would be extremely impractical.

Relative formula mass (Mr) is the total relative mass of a molecule. It is the Ar of each atom in a molecule added together. (e.g. CO2 would be 1 x 12, because there is one carbon, plus 2 x 16, because there are two oxygens, adding to a Mr of 44)

Mr can be used to calculate the mass of a substance that can be obtained from a chemical reaction, or how much of a substance is necessary to neutralise another substance.
This formula triangle is useful in calculating masses:

When the Mr of a substance is equal to the number of grams there are of it, that is one mole. A mole is 6.022 x 10^23 particles. This is called Avagadro's number, or Avagadro's constant.
A mole of gas at room temperature and pressure always takes up 24 dm^3, or 24000 cm^3. 

Section 1 c) Summary

Atoms are made up of a central nucleus, which has a relative positive charge due to its protons. It also contains neutrons. These make up the entire relative mass of the atom.
This is orbited by negatively charged electrons, which are attracted to the positive nucleus. These electrons make up shells, which have capacity: 2,8,8,8,8,8,8.

An atom has equal numbers of protons and electrons, resulting in no overall charge. Electrons can be transferred to other particles, however, or gained from them. This results in the atom gaining a charge and becoming an ion. A negatively charged ion is called a cation and a positively charged ion is called an anion.

When atoms have the same number of protons but a different number of neutrons, they are called isotopes.

All chemical elements are organised in the periodic table.

It is organised in order of atomic number. It fits into different groups and periods based off properties and characteristics. The properties and reactivity of an element can be predicted by the surrounding elements in the table.
Periods are the rows, Groups are the columns.
The periods can tell us the number of shells each atom has, while the groups tell us the number of outer shell electrons they have.
The basic electronic capacity of the shells is 2, 8, 8, 8

Section 1 b) Summary

An atom is the smallest existing chemical particle with an equal number of protons and electrons, and as a result has no charge. Each atom is a chemical element, which can react with each other to form compounds or physically combine to make a mixture. 

A compound is a substance formed by the chemical union of two or more chemical elements, with a definite, unchanging ratio. It has its own properties, different from the properties of its parts, and requires chemical reactions to be separated. 

A mixture is made from different substances that are not chemically bonded. Each of the substances within a mixture retains its own properties, and the ratio is not fixed. The substances are easily physically separated. 

Methods of separation include:

Filtration: Separating insoluble particles from a liquid

Passing a mixture through a filter funnel.

Evaporation: Removing liquid from a solution

Heating a solution to boiling point until the liquid is gone.

Chromatography: Separating controlled substances or dyes

Placing dots on chromatography paper and letting it run up the paper with capillary action.

Distillation: Separating liquids from each other. Simple - two liquids. Fractional - many liquids, involving a fractionating column.

Boiling and condensing liquids of different boiling temperatures. 

Chemical particles disperse through a fluid through diffusion and dilution. Diffusion is the net movement of particles from an area of high concentration to an area of low concentration. 

This can be demonstrated using experiments between hydrochloric acid  and ammonia, or bromine in a glass cylinder, as well as by placing food dye in water. The dispersal of particles can be seen through the experiments described here (specification)