IGCSE Chemistry topics 8 & 9

What name is given to elements in Group 0?

Noble gases

The noble gases are monatomic gases. What does monatomic mean?

Molecules consist of only one atom.

How many electrons do the noble gases have in their outer shell?

Noble gases have full outer shells so most noble gases have 8 electrons in their outermost shell, excluding helium which has 2 in its outer shell.

What does chemically inert mean?

Chemically unreactive

Why are the noble gases chemically inert?

They have full outer electron shells. This is a very stable electron configuration and means the elements are very unreactive.

What is the electron configuration of neon?

The electron configuration of neon is 2, 8

What are the general properties of transition metals?

• Relatively high densities. - High melting points. - Form coloured compounds. - Often act as catalysts.

Fill in the blank

'Transition metals have variable ______' (extended only)

Show that transition metals have variable oxidation states (extended only)

Fe²⁺ and Fe³⁺, Cu⁺ and Cu²⁺, Cr²⁺ and Cr³⁺

Which group do the elements chlorine, bromine and iodine belong to? What is another name for this group of elements?

Group VII, the halogens.

Halogens are diatomic. What does this mean?

They form molecules consisting of 2 atoms. E.g. Cl₂, Br₂ …

What is the colour and state of chlorine at room temperature?

Pale green gas

What is the colour and state of bromine at room temperature?

Red- brown liquid

What is the colour and state of iodine at room temperature?

Grey- black solid

Why are the halogens at different states at room temperature? What is the trend down the group?

At room temperature, chlorine is gaseous, bromine is liquid and iodine is solid because they have different melting and boiling points. As you go down the group, melting and boiling point increase.

What state would you expect the halogens fluorine and astatine to be at room temperature?

Fluorine is above chlorine so should have a boiling point lower than chlorine. This means it would be a gas at room temperature. Astatine is below iodine in Group VII so should have a higher melting point than iodine. Therefore you can predict that it would be a solid at room temperature.

What is trend in colour and density of the Group VII elements?

Colour gets darker down the group. Density increases down the group.

Why do melting and boiling point increase down Group VII?

The molecules get bigger down the group so there are stronger intermolecular forces to overcome during melting / boiling so more energy is required to change state.

When does a halogen displacement reaction occur?

When a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide ions.

Why does reactivity decrease down Group VII?

Group VII elements gain an electron when they react. As you go down Group VII, atomic radius and electron shielding increase. This means that the attraction between the nucleus and outer electrons decreases so it is harder for the atom to gain an electron.

Why will halide ions A only be displaced by halogen B if B is above A in Group VII?

The most reactive halogen (B) will displace the less reactive halogen (A) to become part of the ionic compound. Reactivity increases as you go up the group so B must be higher in Group VII to be more reactive than A.

Which halogens can chlorine displace from an aqueous ionic solution?

Chlorine can displace any halogens below it in Group VII. It will displace iodine and bromine.

Which halogens can't be displaced from an aqueous ionic solution by bromine?

Bromine can't displace any halogens above it in Group VII. These are chlorine and fluorine.

Why can iodine not displace chlorine or bromine from an aqueous ionic solution?

Because reactivity decreases down the group and iodine is below chlorine and bromine Group VII. Displacement will only occur if iodine is more reactive than the halogen in the ionic compound.

Write the word equation for the reaction between chlorine and potassium bromide

Chlorine + potassium bromide → potassium chloride + bromine

Write the word equation for the reaction between bromine and calcium chloride

No reaction will occur because bromine is less reactive than chlorine so chlorine won't be displaced.

Write the balanced symbol equation for the reaction that takes place between bromine and potassium iodide

Br2 + 2KI ⟶ I2 + 2KBr

Which halogens would you expect astatine to be able to displace?

None of them. It is at the bottom of Group VII so has the lowest reactivity.

What colours are solutions of chlorine, bromine and iodine?

Chlorine water - colourless Bromine water - orange Iodine solution - brown

What would you observe when chlorine is added to potassium bromide?

Cl2 + 2KBr → Br2 + 2KCl Colour change from colourless (due to Cl₂) to orange (due to Br₂).

What trends can be seen in group I elements (lithium, sodium and potassium)?

• All relatively soft metals.- Decrease in melting point down the group- Increases in density down the group- Increase in reactivity with water down the group.

How does melting point change down Group I?

Melting point decreases down the group because the strength of the metallic bonds decreases so less energy is required to break these bonds to turn the solid into a liquid.

How does density change down Group I?

Density increases down the group. All Group I elements have low densities and will float on water.

What is the trend in the reactivity with water down Group I?

Reactivity increases down the group.

Why does reactivity increase down Group I?

Group I elements lose an electron when they react. Atomic radius and electron shielding increase down the group so there is weaker attraction between the nucleus and outer shell electron. This means less energy is required to remove this electron from elements further down the group.

Describe the general reaction of a Group I element with water

Vigorous reaction with water, producing hydrogen and an alkaline solution. Bubbles will be seen due to the production of hydrogen.

Using the trend in melting points, predict which element in Group I has the highest melting point

Lithium

Using the trend in density, predict which element has the highest density out of sodium, lithium and caesium

Caesium

What is the periodic table?

A method of classifying and arranging elements.

How is the periodic table arranged?

The elements are arranged in order of increasing atomic number. This places elements in vertical groups (columns) and horizontal periods (rows). Elements in the same period have the same number of electron shells and elements in the same group have the same number of electrons in their outer shell.

Where are metals and non- metals found in the periodic table?

Metals make up most of the periodic table and are found towards the left of the table. Non- metals are found towards the top right of the periodic table.

How does metallic character change across a period?

It decreases across the period.

How does non- metallic character change across a period?

It increases across the period.

Why do elements in the same group have similar chemical properties?

Chemical properties are determined by the number of electrons in the outer shell of an atom. Elements in the same group have the same number of electrons in their outer shell so they react in a similar way.

How many electrons are in the outer shell of a group V element?

Five

What is the charge on group I and group II ions?

Group I and group II elements are metals so they lose electrons to form positive ions. Group I forms 1+ ions. Group II forms 2+ ions.

What is the charge on group VI and group VII ions?

Group VI and group VII elements are non- metals so they gain electrons to form negative ions. Group VI forms 2- ions. Group VII forms 1- ions.

Which group do lithium, sodium and potassium belong to?

Group I

Where are most metals extracted from?

From ores found in the Earth's crust.

What is an ore?

A rock which contains metals, often chemically combined with other substances.

Which metals are found in the Earth's crust as uncombined elements?

Unreactive metals such as gold

Most ores contain metals chemically combined with oxygen. What process must be carried out to extract the metal?

Reduction

How can metals be extracted from their ores?

Reduction with carbon

How can iron be extracted from its oxide, hematite?

Iron is less reactive than carbon so can be extracted by reduction with carbon.

What is used to extract iron from its oxide, hematite?

Hematite, coke, limestone and air, in a blast furnace Hematite

What is the purpose of burning coke (carbon) in the extraction of iron?

• Hot air enters through the bottom of the furnace and moves to the top.- At the bottom of the furnace, the coke burns in the hot air producing carbon dioxide, an exothermic reaction that releases heat to keep the furnace hot.- Carbon + Oxygen -> Carbon dioxide

How is carbon monoxide produced in the extraction of iron?

• The carbon dioxide produced from the burning of coke reacts further with the coke to form carbon monoxide- Carbon dioxide + Carbon -> Carbon monoxide

How is iron produced using carbon monoxide in the extraction of iron?

• The carbon monoxide reduces iron (III) oxide (hematite) to iron in a redox reaction- Iron (III) oxide + Carbon monoxide -> Iron + Carbon dioxide- The pure iron flows to the bottom of the blast furnace to be removed.

What is the purpose of limestone in the extraction of iron?

• The hematite contains other impurities like sand (silicon (IV) oxide), so limestone (calcium carbonate CaCO3 ) is added to helps remove these impurities- CaCO3 thermal decomposes from the heat in the blast furnace into calcium oxide- Calcium carbonate -> Calcium oxide + Carbon dioxide- The calcium oxide reacts with the silicon (IV) oxide to form a 'slag'

What is the main ore that aluminium is extracted from called?

Bauxite

How can aluminium be extracted from its ore?

Aluminium is more reactive than carbon so electrolysis must be used. When the molten ore undergoes electrolysis, the pure metal forms at the cathode.

Give the symbol equation for the burning of carbon (coke) in the extraction of iron (extended only)

Carbon + Oxygen -> Carbon dioxide C(s) + O2(g) -> CO2(g)

Give the symbol equation for the reduction of carbon dioxide to carbon monoxide in the extraction of iron (extended only)

Carbon dioxide + Carbon -> Carbon monoxide CO(g) + C(s) -> 2CO(g)

Give the symbol equation for the reduction of iron (III) oxide by carbon monoxide in the extraction of iron (extended only)

Iron (III) oxide + Carbon monoxide -> Iron + Carbon dioxide Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)

Give the symbol equation for the thermal decomposition of limestone in the extraction of iron (extended only)

Limestone is calcium carbonate CaCO3 Calcium carbonate -> Calcium oxide + Carbon dioxide CaCO3(s) → CaO(s) + CO2(g)

Give the symbol equation for the formation of slag in the extraction of iron (extended only)

Calcium oxide + Silicon (IV) oxide -> Calcium silicate (slag) CaO(s) + SiO₂(s) → CaSiO₃(l)

When aluminium is extracted from aluminium oxide, why is it first dissolved in molten cryolite? (extended only)

Aluminium oxide has a very high melting point. It is dissolved in molten cryolite to reduce the melting point of the electrolyte, reducing energy usage and cost.

What are the electrodes for the electrolysis of aluminium oxide made from? (extended only)

The electrodes are made from graphite (carbon)

Why does the anode for the electrolysis of aluminium oxide need to be regularly replaced? (extended only)

• During electrolysis oxide ions lose electrons at the anode, become oxidised and form oxygen molecules- The carbon the anodes are made from reacts with the oxygen to form carbon dioxide which bubbles away, so the anodes have to be replaced regularly.

What occurs at the cathode during the electrolysis of aluminium oxide? Include the ionic half equation (extended only)

Cathode - Al3+ ions gain electrons to form aluminium atoms, becoming reduced. The half equation is Al3+ + 3e- → Al

What occurs at the anode during the electrolysis of aluminium oxide? Include the ionic half equation (extended only)

Anode - O2- ions loses electrons to form oxygen, becoming oxidised. The half equation is 2O2- - 4e- → O2

What type of reaction is rusting?

Rusting is an oxidation reaction

State the conditions required for the rusting of iron and steel

Iron and steel will rust when they come into contact with water and oxygen

Give examples of barrier methods to prevent rusting

• Oiling- Painting- Greasing- Coating with a layer of plastic

How do barrier methods help to prevent rusting

Barrier methods prevent iron and steel from rusting by preventing the metals from becoming in contact with oxygen and water

How can zinc be used to prevent iron from rusting? (extended only)

Iron can be galvanized with a thin layer of zinc to prevent rusting Zinc acts as a barrier method and sacrificial protection

Explain why sacrificial protection is used to prevent iron from rusting (extended only)

Sacrificial protection is when metals higher in the reactivity series, such as zinc, are used to coat metals lower in reactivity, such as iron. This is because metals that are more reactive than iron will be more likely to get oxidised and lose electrons to form its positive ions.

What is the order of the reactivity series and how can this order be deduced?

The order can be deduced by the different metals reactions with acid, water and reduction with carbon. Potassium Sodium Calcium Magnesium Aluminium (Carbon) Zinc Iron (Hydrogen) Copper Silver Gold

Describe the reaction between potassium and cold water

• The most violent/vigorous reaction with cold water since it is at the top of the reactivity series- Potassium melts and floats, moving rapidly on the surface of the water. A lilac flame will also ignite- Potassium + Water → Potassium hydroxide + Hydrogen- 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)

Describe the reaction between sodium and cold water

• Less vigorous reaction with cold water than potassium since it is below K in the reactivity series- Sodium melts to form a ball that moves around on the surface and fizzes rapidly before it disappears- Sodium + Water → Sodium hydroxide + Hydrogen- 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Describe the reaction between calcium and cold water

• Least vigorous reaction with cold water out of K and Na since it is below both in the reactivity series- Reaction is slower and less violent

Describe the reaction between magnesium and steam

● Magnesium oxide and hydrogen gas will form ● Magnesium + Steam → Magnesium oxide + Hydrogen ● Mg(s) + H2O(g) → MgO(s) + H2(g)

Describe the reaction between the 3 most reactive metals in the reactivity series with dilute HCl

Potassium, sodium and calcium are very reactive so this reaction can ignite, causing an explosion, so is too dangerous to be done in the school lab.

Which metals in the reactivity series will react with dilute HCl?

• Only metals above hydrogen will react with dilute acids.- Magnesium- fast reaction- Zinc and Iron- slightly fast reaction- Copper, silver and gold- no reaction as below hydrogen in the reactivity series

How could the order of reactivity be deduced from experimental results?

• In a displacement reaction, the more reactive metal will replace the less reactive metal in a compound- A less vigorous and slow reaction will usually mean a lower reactivity whereas lots of effervescence (bubbles/fizzing) and quicker reactions are usually higher in the reactivity series- Only metals above hydrogen will react with dilute acids

What is meant by the reactivity of metals? (extended only)

The tendency of a metal atom to lose electrons and form its positive ion.

Describe the reaction between iron and calcium oxide (extended only)

• No reaction will occur- Iron is lower than calcium in the reactivity series so cannot displace calcium

Describe the reaction between sodium and magnesium oxide (extended only)

● Sodium will displace magnesium to form sodium oxide ● Sodium is higher in the reactivity series than magnesium

Why doesn't aluminium appear to undergo oxidation? (extended only)

Aluminium reacts with oxygen in the air to form aluminium oxide (Al₂O₃). This very unreactive oxide coats the surface of the metal, preventing any further oxidation.

What is an alloy?

A mixture containing a metal and another element (metal or non- metal). Alloys are stronger and harder than pure metal so are more useful

Give examples of alloys

Brass - mixture of copper and zinc Stainless steel- mixture of iron and other elements such as chromium, nickel and copper

Why is gold jewellery often an alloy?

Gold is very soft so it must be alloyed with another metal to make it harder and more suitable for jewelry.

How and why is zinc used to make brass?

Zinc is alloyed with copper to increase the strength and hardness of the material.

How is iron able to form steel alloys with different properties and uses?

Different additives can be added to iron to make different forms of steel. The amount of carbon added to the iron affects how hard the alloy is.

MILD steel has 0.25% carbon and high carbon steel has 2.5% carbon. Which steel is harder?

High carbon steel is harder because there are more carbon atoms distorting the uniform layers of iron atoms.

Why is stainless steel used to make cutlery?

Stainless steel is used to make cutlery as it is harder and resistant to corrosion. Whereas pure iron is soft and rusts easily

Draw diagrams to show the structure of an alloy

The atoms in alloys are different sizes

Why are alloys harder than pure metals, using explanations of their structure (extended only)

Atoms in pure metals are arranged in uniform rows which can slide over each other easily, making them very malleable. The atoms in alloys are different sizes which distorts the layers meaning they are unable to slide over one another, increasing hardness.

Draw diagrams to compare the structure of brass (alloy) and copper (metal) (extended only)

Pure copper metal vs Brass

Give the physical properties of metals

• Good electrical and thermal conductivity- Malleable and ductile- Shiny- Some metals have low density