The early periodic table

• Mendeleev: – Also arranged elements according to atomic weights – Elements repeat properties periodically (regularly),

also placed in columns, or groups – Gaps left for undiscovered elements – Three new elements discovered in his lifetime that

fitted these gaps

C3.1.1

• Newlands: – Arranged elements according to atomic weights – ‘Law of Octaves’ similar properties repeated every 8th

element – Some elements placed in inappropriate groups, due to

strictly following order of weights – Sometimes more than one element in each ‘position’

The modern periodic table

• Electrons, protons and neutrons were discovered early in the 20th century

• Elements now arranged by atomic (proton) numbers • All elements now in appropriate groups • Elements in the same group have the same number of

electrons in their highest occupied energy level (outer shell)

C3.1.2

Group 1

3Li 2, 1

11Na 2, 8, 1

19K 2, 8, 8, 1

37Rb 2, 8, 18, 8, 1

55Cs 2, 8, 18, 18, 8, 1

Group 2

4Be 2, 2

12Mg 2, 8, 2

20Ca 2, 8, 8, 2

38Sr 2, 8, 18, 8, 2

56Ba 2, 8, 18, 18, 8, 2

Trends within the periodic table: Group 1 - the alkali metals

• Physical properties: – Low density (the first three elements in the group are less

dense than water) – The further down the group an element is:

• the more reactive the element • the lower its melting point and boiling point

• Chemical properties: – All react with non-metals to form ionic compounds in which

the metal ion carries a charge of +1 – The compounds are white solids that dissolve in water to form

colourless solutions – All react with water, releasing hydrogen – All form hydroxides that dissolve in water to give alkaline

solutions

C3.1.3

Trends within the periodic table: The transition elements

• Compared with the elements in Group 1, transition elements: – have higher melting points (except for mercury) and

higher densities

– are stronger and harder

– are much less reactive and so do not react as vigorously with water or oxygen

• Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts

C3.1.3

The modern periodic table

C3.1.2

• What is the modern periodic table arranged by?

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

The early periodic table

C3.1.1

Why was Mendeleev’s periodic table accepted, where Newland’s was not? How did Mendeleev decide on the order of the elements in the periodic table?

Trends within the periodic table: The transition elements

C3.1.3

• Name five ways transition elements differ to group 1 metals?

Trends within the periodic table: Group 1 - the alkali metals

C3.1.3

• Write a word and symbol equation for the reaction of a group 1 metal with water.

• How would you expect the reactivity of rubidium to compare with lithium. Explain your reason.

Trends within the periodic table: Group 7- the halogens

• The elements in Group 7 of the periodic table react with metals to form ionic compounds in which the halide ion carries a charge of –1

• In Group 7, the further down the group an element is: – the less reactive the element

– the higher its melting point and boiling point

• A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

C3.1.3

Trends within the periodic table: Explaining the trends

• The trends in reactivity within groups in the periodic table can be explained because the higher the energy level of the outer electrons:

– the more easily electrons are lost

– the less easily electrons are gained

• Group 1 elements react by losing an electron

– Li is less reactive than K, because its outer electron is nearer to the attractive nucleus so is held more tightly.

• Group 7 elements react by gaining an electron

– So F2 is more reactive than I2, because the gap in its outer shell, into which an electron would go, is closer to the nucleus, so electron attracted more strongly.

C3.1.3

Higher tier only

Higher tier only

Hard and soft water

• Hard water contains dissolved compounds, usually of calcium or magnesium ions – The compounds are dissolved when water comes into

contact with rocks

• There are two types of hard water – Permanent hard water remains hard when it is boiled

– Temporary hard water is softened by boiling

– Higher Tier: Temporary hard water contains hydrogencarbonate ions (HCO3

-) that decompose on heating to produce carbonate ions which react with calcium and magnesium ions to form precipitates and the water becomes soft.

C3.2.1

Hard and soft water: consequences

• Soft water readily forms lather with soap • Hard water reacts with soap to form scum and so

more soap is needed to form lather – Soapless detergents do not form scum

• Using hard water can increase costs because more soap is needed. When temporary hard water is heated it can produce scale that reduces the efficiency of heating systems and kettles

• Hard water has some benefits, because calcium compounds are good for the development and maintenance of bones and teeth and also help to reduce heart disease

C3.2.1

Trends within the periodic table: Explaining the trends

C3.1.3

• Explain why lithium is less reactive than potassium.

• Explain why fluorine is more reactive than iodine.

Trends within the periodic table: Group 7- the halogens

C3.1.3

• Write a word and symbol equation for a group 7 element with a group 1 element.

• How and why does reactivity change within the halogen group?

Hard and soft water: consequences

C3.2.1

• What forms when hard water reacts with soap?

• Describe the health benefits of hard water.

Hard and soft water

C3.2.1

• What causes water to be ‘hard’?

• Describe the difference between permanent and temporary hard water.

Hard and soft water: Removing hardness

• Hard water can be made soft by removing the dissolved calcium and magnesium ions. This can be done by: – adding sodium carbonate, which reacts with the

calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate

– using commercial water softeners such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column

C3.2.1

Purifying water

• For humans, drinking water should have sufficiently low levels of dissolved salts and microbes

• Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality • Chlorine may be added to drinking water to kill

microbes and fluoride may be added to improve dental health (pros and cons?)

• Pure water can be produced by distillation

C3.2.2

NB: Detailed knowledge of specific water filters is not required.

Energy from reactions: Comparing the energy released by fuels

• The relative amounts of energy released when substances burn can be measured by simple calorimetry, e.g. by heating water in a glass or metal container

C3.3.1

• Using: Q = mc ΔT, where: Q = energy, in Joules (J) m = mass of substance heated

(usually water) c = specific heat capacity

(energy required to heat one gram of a substance up by 1°C)

ΔT = change of temperature

Energy from reactions: Energy transfers in solution

• The amount of energy released or absorbed by a chemical reaction in solution can be calculated from the measured temperature change of the solution when the reagents are mixed in an insulated container

• This method can be used for reactions of solids with water or for neutralisation reactions

• Again, this will use Q = mc ΔT, but this time ‘m’ is the mass of both solutions (or solid + water) used

C3.3.1

Purifying water

C3.2.2

• What is the difference between ‘pure’ water and ‘drinking’ water?

• Why is chlorine added to drinking water?

Hard and soft water: Removing hardness

C3.2.1

• Describe two ways in which permanent hardness can be removed.

Energy from reactions: Energy transfers in solution

C3.3.1

• The energy from burning 0.5 g of propane was transferred to 100 cm3 of water to raise its temperature by 20°C. Calculate the energy transferred.

Energy from reactions: Comparing the energy released by fuels

C3.3.1

• What do each of the symbols in Q = mc ΔT stand for?

Energy from reactions: Energy level diagrams

• Simple energy level diagrams show the relative energies of reactants and products, and can show activation energy and the overall energy change of a reaction (ΔH)

C3.3.1

energy

Exothermic

energy

reactants

products

-ΔH

time

Endothermic

energy

reactants

products

+ΔH

time Endothermic, with activation energy (Eact)

reactants

products

+ΔH

Eact

time

Energy from reactions: Calculations using bond energies

• During a chemical reaction:

– energy must be supplied to break bonds

– energy is released when bonds are formed

ΔH = sum of bonds broken – sum of bonds made

• In an exothermic reaction, the energy released from forming new bonds is greater than the energy needed to break existing bonds: (-ΔH)

• In an endothermic reaction, the opposite is true: (+ΔH)

C3.3.1

Higher tier only

Higher tier only

Energy from reactions: Catalysts & fuel issues

• Catalysts provide a different pathway for a chemical reaction that has a lower activation energy

• Hydrogen can be burned as a fuel in combustion engines:

hydrogen + oxygen water

– So, no greenhouse gases produced

– But, energy is needed to produce the hydrogen

• It can also be used in fuel cells that produce electricity to power vehicles.

C3.3.1

NB: Knowledge of the details of the reactions in fuel cells is not required

Analysing substances: Tests for positive ions – flame tests

• Many metal ions will produce distinctive colours when a crystal or a solution of a metal compound is held in a flame:

– lithium compounds result in a crimson flame

– sodium compounds result in a yellow flame

– potassium compounds result in a lilac flame

– calcium compounds result in a red flame

– barium compounds result in a green flame

C3.4.1

Energy from reactions: Calculations using bond energies

C3.3.1

Bond Bond Energy (kJ/mole) H−H 436 Cl−Cl 243 H−Cl 432

Hydrogen and chlorine react to form hydrogen chloride gas:

H−H + Cl−Cl → 2 × (H−Cl)

The table below shows the bond energies relevant to this reaction.

Calculate the bond energy for this reaction.

Energy from reactions: Energy level diagrams

C3.3.1

energy

reactants

products

-ΔH

time

energy

reactants

products

X

time

What sort of reaction is represented by this energy level diagram?

What sort of reaction is this, what is

represented by ‘X’?

Analysing substances: Tests for positive ions – flame tests

C3.4.1

• Describe how to complete a flame test

• Which ion is present if the flame turns red?

• Which ion is present if the flame turns orange?

Energy from reactions: Catalysts & fuel issues

C3.3.1

• How does a catalyst work to increase the rate of a reaction?

• Give an example of a catalyst in a reaction.

• What is the main advantage of using hydrogen as a fuel?

Analysing substances: Tests for positive ions - NaOH

• Some metal ions will form a precipitate (solid) when added to solution of sodium hydroxide (NaOH(aq)) – Aluminium, calcium and magnesium ions form white

precipitates with sodium hydroxide solution • only the aluminium hydroxide precipitate dissolves in excess

sodium hydroxide solution

– Copper(II) (Cu2+) forms a blue precipitate

– Iron(II) (Fe2+) forms a green precipitate (which quickly turns brown due to oxidation with oxygen in the air)

– Iron(III) (Fe3+) forms a brown precipitate

C3.4.1

Analysing substances: Tests for negative ions

• Carbonates react with dilute acids to form carbon dioxide: – Carbon dioxide produces a white precipitate with

limewater, which turns the limewater cloudy

• Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid: – Silver chloride is white

– Silver bromide is cream

– Silver iodide is yellow

• Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid

C3.4.1

Analysing substances: Titrations

• The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator

• You should be able to describe a titration that would allow a successful result to be obtained, including: – solution of unknown concentration in (conical) flask,

volume measured using pipette – indicator in (conical) flask – Solution of known concentration in burette – white tile under flask (to make colours easier to see) – slow addition, drop-wise – Swirling the mixture (to ensure it mixes quickly) – colour change when end (neutralisation) point is reached – volume of known solution added is recorded

C3.4.1

Analysing substances: Titrations

• As the concentration of one of the reactants is known, the results of a titration can be used to find the concentration of the other reactant – You may also be asked to then convert it from mol/dm3 to

g/dm3

• Method: 1. Calculate number of moles of acid used 2. Write balanced equation for reaction 3. Using moles of acid information, deduce number of

moles of alkali required 4. Calculate concentration of alkali • This process also works the same in reverse.

number of moles = volume (cm3) x concentration (mol/dm3) 1000

C3.4.1

Higher tier only

Higher tier only

Analysing substances: Tests for negative ions

C3.4.1

• Describe how to test for negative ions

• What acid is needed to test for Halide ions?

• What colour precipitate does silver iodide form?

Analysing substances: Tests for positive ions - NaOH

C3.4.1

• Describe how to carry out a precipitation test for a positive ion.

• What colour precipitate forms when copper forms?

• What colour precipitate forms when Iron (III) forms?

Analysing substances: Titrations

C3.4.1

Higher tier only

Higher tier only

• Recall the equation for calculating the number of moles.

• 27.5 cm3 of 0.2 mol/dm3 hydrochloric acid is needed to titrate 25.0 cm3 of sodium hydroxide solution. What is the concentration of the sodium hydroxide solution?

Analysing substances: Titrations

C3.4.1

Recall the method for completing a titration.

What may cause the actual results to differ slightly from the theoretical?

Making ammonia

• The raw materials for the Haber process are nitrogen and hydrogen. – Nitrogen is obtained from the air – Hydrogen may be obtained from natural gas or other

sources (e.g. electrolysis of water)

• The purified gases are passed over a catalyst of iron at a high temperature (about 450 °C) and a high pressure (about 200 atmospheres). Some of the hydrogen and nitrogen reacts to form ammonia. The reaction is reversible so ammonia breaks down again into nitrogen and hydrogen:

nitrogen + hydrogen ammonia • On cooling, the ammonia liquefies and is removed • The remaining hydrogen and nitrogen are recycled

C3.5.1

Equilibrium – what is it?

• When a reversible reaction occurs in a closed system, equilibrium is reached when the reactions occur at exactly the same rate in each direction

• The relative amounts of all the reacting substances at equilibrium depend on the conditions of the reaction, such as:

– Temperature

– Pressure

C3.5.1

Higher tier only

Higher tier only

Equilibrium – effect of temperature

• If the temperature is raised, the yield from the endothermic reaction increases and the yield from the exothermic reaction decreases

• If the temperature is lowered, the yield from the endothermic reaction decreases and the yield from the exothermic reaction increases

• The Haber process is exothermic, so a higher temperature produces less ammonia!

C3.5.1

Higher tier only

Higher tier only

Equilibrium – effect of pressure

• In gaseous reactions, an increase in pressure will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction.

• In the case of the Haber process:

N2 + 3H2 2NH3

– The right hand side is favoured by higher pressure, as it has two molecules, compared to four

– So higher pressure means higher yield of ammonia

C3.5.1

Higher tier only

Higher tier only

Equilibrium – what is it?

C3.5.1

Higher tier only

Higher tier only

• Define equilibrium in areaction

Making ammonia

C3.5.1

• What kind of reaction is there in making ammonia?

• What are the ideal industrial conditions for the Haber process?

Equilibrium – effect of pressure

C3.5.1

Higher tier only

Higher tier only

• Which direction of the reaction does increasing pressure effect?

• Why is 200 atmospheres chosen for the Haber process?

Equilibrium – effect of temperature

C3.5.1

Higher tier only

Higher tier only

• Which direction of the reaction does increasing temperature effect?

• Why is 450C chosen for the Haber process?

Alcohols

• Alcohols contain the functional group –OH. Methanol (CH3OH), ethanol (C2H5OH) and propanol (C3H7OH) are the first three members of a homologous series of alcohols

• They all: – dissolve in water to form a neutral solution – react with sodium to produce hydrogen – burn in air (must be able to write balanced symbol equations for

combustion reactions) – are used as fuels and solvents, and ethanol is the main alcohol

in alcoholic drinks

• Ethanol can be oxidised to ethanoic acid, either by chemical oxidising agents or by microbial action. Ethanoic acid is the main acid in vinegar

C3.6.1

Structural formula: C2H5OH

Displayed formula:

H H

H H

C C H O H

Carboxylic acids

• Carboxylic acids have the functional group –COOH • Methanoic acid (CHOOH), ethanoic acid(CH3COOH)

and propanoic acid (C2H5COOH) are the first three members of the homologous series

• Carboxylic acids: – dissolve in water to produce acidic solutions – react with carbonates to produce carbon dioxide – react with alcohols in the presence of an acid catalyst to produce esters – do not ionise completely when dissolved in water and so

are weak acids – aqueous solutions of weak acids have a higher pH value

than aqueous solutions of strong acids with the same concentration

C3.6.2

Higher tier only

Higher tier only

Structural formula: CH3COOH

Displayed formula:

H

H

C C H O

H

O

NB: You do not need to know any equations for these reactions

Esters

• Ethyl ethanoate is the ester produced from ethanol and ethanoic acid.

• Esters have the functional group –COO–

• They are volatile compounds with distinctive smells and are used as flavourings and perfumes

• You should be able to name ethyl ethanoate, and recognise if a compound is an ester from its name or its structural formula.

C3.6.3

Structural formula: CH3COOCH2CH3

Displayed formula:

H

H

C C H O

C

O H

H

C H

H

H

Carboxylic acids C3.6.2

• What is a homologous series?

• What is the functional group for carboxylic acids?

• List the properties of carboxylic acids

Alcohols

C3.6.1

• What is a homologous series?

• What is the functional group for alcohols acids?

• Draw the structure of propanol.

• List the features of all alcohols.

Esters

C3.6.3

• What is the functional group for Esters?

• List the 2 main uses of esters.