Welcome to
AS Chemistry Revision Session

Mass SpectrometerAtomic Structure and Periodic TableOrganic ChemistryThermochemistryStructure & BondingKineticsEquilibriaInorganic Chemistry

Programme for morning

9:10 - 9:20 Introduction9:20 - 9:45 Mass Spectrometer9:45 - 10:10 Atomic Structure & Periodic Table10:10 - 10:35 Organic Chemistry10:35 - 10:55 Break10:55 - 11:20 Organic Chemistry (continued)11:20 - 12:00 Thermochemistry12:00 - 12:30 Structure & Bonding12:30 - 12:50 Kinetics & Equilibria12:50 - 13:10 Key aspects of Inorganic Chem.

Introduction

This session should get you off to a good start and encourage you to continue.We will revise important themes that underpin the whole course and deal with ideas likely to crop up in questionsWe do not have time to cover everything!The revision pack includes answers to numerical questions and many other problemsTake the pack away and continue to use it to support your revision.

Advice about revision

Course Handbook provides general advice about revision techniquesFor each study unit, learn the meaning of relevant key words in Course HandbookFor topics requiring a lot of factual recall e.g. organic chemistry, and group chemistry, learn the basic facts first.Make use of spider diagrams (for organic) and revision cards (for group chemistry) to do this. Copies supplied todayDont forget to learn tests for ions for paper 3B.Self assessment questions on s-block, group 7 and tests for ions are included in todays pack

Mass Spectrometer the instrument

Mass Spectrometer ion formation

Electron bombardment positive ions formed

Mass Spectrometer - acceleration

Electric field - negatively charged plates further down tube accelerate positive ions

Mass Spectrometer - deflection

Magnetic field deflects positive ions

the greater the mass the less the deflection

Mass Spectrometer - detection

Ions are detected and record made mass spectrum is a plot of relative abundance against m/e value

Mass Spectrum Problem

This shows the major peaks in the mass spectrum of a ketone, XIdentify the peak caused by the molecular ionSuggest the formulae of the fragmented ions which give the peaks at m/e values of 15, 29, 43 and 57.Deduce the structural formula of X

Periodic Table Vertical Trends

Atomic radius increases down groupsIncreasing number of shells occupiedIncrease in nuclear charge is matched by equal increase in number of screening electrons1st ionisation energy decreases as distance of outer electron from nucleus increasesElements become more metallic increasing ease of positive ion formation

Periodic Table Horizontal Trends

Atomic radius decreases across periodIncrease in nuclear charge but no increase in number of screening electrons1st ionisation energy increases across periodElements become less metallic decreasing ease of positive ion formationTendency to form negative ions increases as atomic radius decreases

Alkanes

Alkenes

Alcohols

Halogenoalkanes

Synthetic Pathways - Example

List the compounds you know can be made directly from starting materialAlongside the first list, make another list of the compounds that you know can be converted directly into the productFind a link between the 2 lists if you are lucky the same compound will appear in both (if not you will need to convert a compound from the 1st list into one from the 2nd and you will need 3 steps)

iodoethane 1,2-dibromoethane

Synthetic Pathways - Example

iodoethane 1,2-dibromoethane

CH3CH2I

CH3CH2OH

CH3CH2CN

CH3CH2NH2

CH2 == CH2

CH2BrCH2Br

CH2 == CH2

Answer

Synthetic Pathways Examples 1-3

Synthetic Pathways Examples 4-6

Thermochemical calculations

Enthalpy of formation from enthalpy of combustion dataEnthalpy change for any reaction from enthalpy of formation dataEstimating enthalpy change from bond enthalpy data

Thermochemical experiments

Calculate energy released / gained for the quantities actually used = mcpDTCalculate number of moles of reactants taking part in reactionScale up energy change to the number of moles shown in the thermochemical equation.Insert the correct sign for DH

Bonding - Covalent

A covalent bond is the electrostatic force of attraction of two nuclei towards a shared pair of electrons between them, one electron in the shared pair coming from each atom. A dative covalent bond is the electrostatic force of attraction of two nuclei towards a shared pair of electrons between them, both electrons in the shared pair coming from the same atom.

Bonding Molecular Structures

Simple molecular structures have relatively low m.p.s and b.p.sSubstances with big molecules e.g. polythene soften on heating as chains move over each other

Molecular Structures (simple molecules e.g. water, or big molecules e.g. polythene)

These are characterised by having strong covalent bonds within their molecules but weak attractions between their molecules (i.e. weak intermolecular forces).

SIMPLE MOLECULAR STRUCTURE

Shapes of Molecules

Electron-pair repulsion theory - electron clouds repel each other and adopt an arrangement in space so that repulsion between them is at a minimum.Count the number of bond pairs and lone (non-bonded) pairs around the central atom(s). For the purposes of predicting molecular shapes, multiple bonds should be considered as one electron cloud.The molecular shape is described in terms of the geometric arrangement of atoms (not the arrangement of electron clouds)

Predicting bond angles

Common molecular shapes include linear, trigonal planar, V-shaped, tetrahedral, trigonal pyramidal, trigonal bipyramidal and octahedral.Lone-pair orbitals are more effective in repulsion than bond pairs (Why is this?)Multiple bonds are more effective in repulsion than single bonds.

Giant Molecular Structures 1

Giant Molecular (Covalent Network) Structures are formed by huge numbers of atoms being linked together by covalent bonds to form networks of atoms. The atoms may be linked in layers (e.g. in graphite) or in 3-dimensional networks (e.g. diamond and silicon dioxide) with strong bonds throughout the network.

SILICON DIOXIDE

Giant Molecular Structures 2

Strong covalent bonds throughout

Weak Van der Waals forces between layers

Strong covalent bonds within layers

DIAMOND

GRAPHITE

Giant Molecular Structures 3

Graphite is soft & slippery - weak Van der Waals forces between layers - slip over one another easily. Diamond is hard - strong covalent bonds throughout.Both have high m.p.s and b.p.s because a large number of strong covalent bonds have to be broken to break down giant structures into small enough fragments to produce freely moving particles. In graphite, each C atom forms only 3 covalent bonds - leaving one outer electron not involved in bonding. Spare electrons are delocalised in between the layers - they are mobile and so graphite conducts electricity. Diamond is an electrical insulator because all of the outer electrons of the C atoms are used in bonding.

Bonding - Ionic

Strong ionic bonds throughoutHigh m.p. & b.p.Good electrical conductors when molten or in aqueous solutionSoluble in polar solvents; insoluble in non-polar solventsHard, brittle may cleave along definite planes

An ionic bond is the electrostatic force of attraction between oppositely charged ions, formed as a result of complete electron transfer.

Cl- Na+

GIANT IONIC STRUCTURE

Bonding - Metallic

Malleable bonds non-directional and layers can slip over each other without bonds being broken High b.p.s strong metallic bonds throughoutGood conductors of electricity (and heat) electrons are mobile (& transfer energy between atoms)

Metallic bonds are the electrostatic forces of attraction between the cations in a metallic lattice and the delocalised valence electrons that surround them.

GIANT METALLIC STRUCTURE

Van der Waals Forces

These are the weak electrostatic forces of attraction between molecules where one end of a temporary dipole, set up in a molecule as a result of the fluctuating electron cloud, is attracted towards the opposite end of a dipole induced in a neighbouring molecule. Van der Waals forces are the only intermolecular force present in non-polar substances.Van der Waals forces increase in strength with increasing molecular size (i.e. increasing number of electrons per molecule).Van der Waals forces can also be affected by molecular shape they increase in strength with increasing surface area of contact between molecules.

Dipole-dipole attractions

These are the electrostatic forces of attraction between the oppositely charged ends of permanent dipoles in neighbouring molecules.They exist in addition to Van der Waals forces in polar substances.A covalent bond is polarised if there is a difference in electronegativity between the atoms involved.The molecule as a whole will not be polar if it is symmetrical and the effects of the polarised bonds cancel each other out.

Hydrogen Bonds

This is the electrostatic force of attraction between a proton that has been denuded of electrons, by direct attachment to a highly electronegative atom such as N, O or F, and the lone pair on another highly electronegative atom.Hydrogen bonding leads to stronger intermolecular forces than ordinary dipole-dipole attractions

Polarisation of anions

This leads to some covalent character in compounds that are primarily ionicPolarisation of the anion is caused by the neighbouring cationIt leads to distortion of its electron cloud (no longer spherical) and some sharing of electron density, i.e. covalent characterThe polarising power of the cation is greatest when it is small and has a large positive charge (i.e. has a high charge density)The polarisability of the anion is greatest when it is large and has a large negative charge

Kinetics Collision Theory 1

The collision frequency is directly proportional to the surface area of contact between the two phases in a heterogeneous reaction. Therefore increasing the surface area of contact leads to an increase in reaction rate Increasing concentration (or pressure) of reactant causes the reacting particles to be, on average, closer together. This increases the collision frequency between reacting particles and hence increases reaction rate.

Kinetics Collision Theory 2

Activation energy is the minimum energy needed upon collision if it is to lead to reaction, i.e. be successful.Increasing the temperature increases the average kinetic energy of the reacting molecules and so a greater proportion of collisions will have the necessary activation energy. This leads to an increase in rate.Addition of a catalyst allows the reaction to take place via an alternative pathway which has a lower overall activation. The reaction rate is increased because a greater proportion of collisions will now have the required activation energy.

Maxwell-Boltzmann Distribution

Fraction of molecules at temp T1 with required activation energy is proportional to the shaded area under red curve

Temperature T1

Higher Temperature T2

Fraction of molecules at temp T2 with required activation energy is proportional to the shaded area under blue curve much bigger

Lower activation energy if catalyst present

Fraction of molecules with required activation energy is now much bigger at either temperature

Kinetic & Energetic Stability

The enthalpy of formation of aluminium oxide is 1676 kJ mol-1. However aluminium does not corrode readily, and does not burn unless the temperature is extremely high. Comment on the thermodynamic and kinetic stability of aluminium.

2Al(s) +1O2(g)

Al2O3(s)

Aluminium oxide is thermodynamically stable relative to its constituent elements

DH = 1676 kJ mol-1

Aluminium is thermodynamically unstable relative to aluminium oxide

high activation energy

Aluminium is kinetically stable relative to aluminium oxide

Moving the position of equilibrium
N2 (g) + 3H2 (g) 2NH3 (g); DH = -92 kJ mol-1

Applied change

Position of equilibrium always moves in direction that counteracts applied change.

Remove some ammonia to decrease its concentration

Position of equilibrium moves in direction which increases concentration of ammonia, i.e. to right.

Decrease the temperature

Position of equilibrium moves in direction which increases temperature, i.e. in exothermic direction which is to the right.

Increase the total pressure

Position of equilibrium moves in direction which decreases total pressure, i.e. in direction which produces fewer moles of gas, which is to the right.

(In the equation there are 4 moles of gas on the left, and two moles on the right.)

Kinetics & Equilibria

Factor

Effect on reaction rate

Effect on position of equilibrium

Increase total pressure.

Increases rate of forward reaction if it involves a gas and increases rate of reverse reaction if it involves a gas.

Moves in direction to produce fewer gas molecules.

Increase temperature.

Increases rate of forward and backward reaction, but not to the same extent.

Moves in endothermic direction.

Add a catalyst.

Increases rate of forward and backward reactions to same extent.

No effect.

Increase concentration of a reactant.

Increases rate of forward reaction.

Moves in favour of products.

Industrial Examples

Be able to apply the principles of kinetics and equilibria three examples of industrial process to predict the optimum conditions for achieving high yield and ratebe aware that the actual conditions used are often a compromise and that cost also needs to be taken into accountHaber Process for manufacture of ammonia: N2 (g) + 3H2 (g) 2NH3 (g); DH = -92 kJ mol-1The manufacture of nitric acid: 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g); DH = -950 kJ mol-1 Contact Process for the manufacture of sulphuric acid: 2SO2(g) + O2(g) 2SO3(g) DH = -197 kJ mol-1

Aspects of Inorganic Chemistry

Learn key reactions via summary cardsReview learning of halogens nowCheck learning using self-assessment questions and answersLearn Tests for Ions for Paper 3B

Trend in thermal stability of nitrates & carbonates of s-block metals

Ionic radius of cation decreasesTherefore charge density increasesTherefore polarising power increasesThis leads to greater weakening of NO or CO bonds in anion

On going UP the groups, compounds get easier to decompose, i.e. need lower temperature to bring about decomposition. This is because:

End of Presentation

S-Block MetalsHalogensChlor-Alkali IndustryMoles (further practice)Tests for ionsAtomic Structure FAQs

Further independent use of pack could include:

m/e

Relative abundance

B = 29

E = 72

C = 43

A = 15

D = 57

CH

4

methane

mixture of substitution products:

CH

3

Cl, CH

2

Cl

2

, CHCl

3

, CCl

4

chloromethane, dichloromethane, etc.

Cl

2

uv light

complete combustion

(xs oxygen)

C

O

2

+

H

2

O

carbon dioxide + water

(incomplete combustion gives carbon monoxide

and/or carbon instead of carbon dioxide)

CH

3

CH

==

CH

2

propene

CH

3

CHBr

CH

3

2-bromopropane

CH

3

CH

BrCH

2

B

r

1,2-dibromopropane

CH

3

CH

2

CH

3

propane

Br

2

inert solvent

H

2

Ni catalyst

HBr(aq)

alkaline

KMnO

4

CH

3

CH

OHCH

2

OH

propane-1,2-diol

C

C

H

H

H

CH

3

C

H

C

C

H

H

H

C

H

H

CH

3

CH

3

n

heat, pressure,

catalysts

(polymerisation)

poly(propene)

CH

3

CH

==

CH

2

propene

CH

3

CH

2

CH

2

I

1-iodopropane

CH

3

CH

2

CH

2

B

r

1-bromopropane

CH

3

CH

2

CH

2

C

l

1-chloropropane

CH

3

CH

2

CH

2

OH

propan-1-ol

KBr, conc H

2

SO

4

heat under reflux

PCl

5

red P, I

2

heat under reflux

conc H

2

SO

4

heat (dehydration)

acidified K

2

Cr

2

O

7

heat (mild oxidation)

CH

3

CH

2

CH

O

propanal

xs acidified K

2

Cr

2

O

7

heat under reflux

CH

3

CH

2

C

O

2

H

propanoic acid

Oxidation of Secondary Alcohols

CH

3

CH

OH CH

3

propan-2-ol

acidified K

2

Cr

2

O

7

heat

CH

3

C

OC

H

3

propanone

CH

3

CH

==

CH

2

propene

CH

3

CH

2

CH

2

OH

propan-1-ol

CH

3

CH

2

CH

2

CN

butanenitrile

CH

3

CH

2

CH

2

NH

2

propylamine

CH

3

CH

2

CH

2

I

1-iodopropane

KOH(aq)

heat under reflux

ethanolic KOH

heat under reflux

ethanolic KCN

heat under reflux

ethanolic NH

3

heat in sealed tube

CH

3

CH

2

I

iodopropane

CH

2

==

CH

2

ethene

CH

2

Br

CH

2

Br

1,2-dibromethane

ethanolic KOH

heat under reflux

Br

2

inert solvent

CH

2

==

CH

2

ethene

CH

3

CH

2

B

r

bromoethane

CH

3

CH

2

CN

propanenitrile

HBr(aq)

ethanolic KCN

heat, reflux

ethanolic KOH

heat, reflux

Br

2

inert solvent

CH

3

CH

2

CH

2

Br

1-bromopropane

CH

3

CH

==

CH

2

propene

CH

3

CH

BrCH

2

B

r

1,2-dibromopropane

aqueous KOH

heat, reflux

acidified K

2

Cr

2

O

7

heat

CH

3

CHI

CH

3

2-iodopropane

CH

3

C

OC

H

3

propanone

CH

3

CHOH CH

3

propan-2-ol

CH

2

==

CH

2

ethene

CH

2

BrCH

2

B

r

1,2-dibromoethane

CH

3

CH

2

OH

ethanol

conc H

2

SO

4

heat

Br

2

inert solvent

CH

3

CH

2

I

iodoethane

CH

3

CH

2

N

H

2

ethylamine

CH

3

CH

2

OH

ethanol

red P, I

2

heat, reflux

ethanolic NH

3

heat, sealed tube

acidified K

2

Cr

2

O

7

heat

CH

3

CH

2

CH

2

OH

propan-1-ol

CH

3

CH

2

CH

O

propanal

CH

3

CH

2

C

O

2

H

propanoic acid

xs acidified K

2

Cr

2

O

7

heat under reflux

Number of

molecules

with a

particular

energy

Kinetic Energy

E

a

E

a

'