Edexcel ALi Unit 1

What is the pattern between Periodic Table position and the charge on simple ions?

(Extended later in the course)

Group 1/2/3 ions have 1+/2+/3+

Group 7/6/5 ions have 1-/2-/3-

Transition metals have varying charges.

Describe the significance of ions ending in ‘ate’ and ‘ide’ and state the ion that is anomalous to this rule.

(Extended later in the course)

’ide’ are single-atom negative ions,

‘ate’ polyatomic negative ions with oxygen.

The exception is hydroxide OH⁻

State the formulae of nitrate, carbonate, sulphate, hydroxide and ammonium ions.

NO₃⁻

CO₃²⁻

SO₄²⁻

OH⁻

NH₄⁺

State the ions of zinc, silver, copper and iron.

Zn²⁺

Ag⁺

Cu⁺ (Cu²⁺ most common)

Fe²⁺ (Fe³⁺ most common)

State the formula of water, carbon dioxide, carbon monoxide, ammonia, hydrogen peroxide and sulphur dioxide.

H₂O

CO₂

CO

NH₃

H₂O₂

SO₂

State the 4 general reactions from GCSE that are expected A Level knowledge.

water + metal → hydroxide + H₂

acid + metal → salt + H₂

acid + base/alkali → salt + H₂O

acid + carbonate → salt + H₂O + CO₂

Define displacement and precipitation reactions

Displacement: A more reactive element (metal or halogen) replaces a less reactive element in a compound.

Precipitation: Aqueous solutions react to form an insoluble solid called a precipitate.

State 5 ‘rules of thumb’ for deciding states.

① acids always aq

② ionics s or aq

③ O₂ N₂ F₂ Cl₂ H₂ CO₂ are g

④ H₂O is l

⑤ hydrocarbons C₁ to C₄ are g

What is an ionic equation?

A simplified equation showing the ions that take part in a reaction, with spectator ions removed.

Define isotopes.

Atoms with the same number of protons but different numbers of neutrons.

Describe the chemical and physical properties of isotopes.

Same chemical properties because same electronic configuration.

Very similar physical properties because only slightly different atomic masses.

Define relative isotopic mass.

The mass of an atom relative to 1/12th of the mass of a ¹²C atom.

Define relative atomic mass.

The weighted mean mass of the atoms of an element relative to 1/12th of the mass of a ¹²C atom.

What instrument is used to detect isotopes and their relative abundance, and what are the 4 key stages in the technique?

Mass spectrometer

① Sample is ionised.

② Positive ions accelerated into the machine.

③ Ions are separated according to mass.

④ Ions detected by mass & relative abundance.

In mass spectrometry what is

a) the parent peak and

b) the base peak on a spectrum?

Parent peak – the peak of highest mass/charge (ie furthest to right) and represents the unfragmented ion.

Base peak – the highest/tallest peak representing the most stable fragment ion.

Why can some mass-spectrum peaks appear at half the expected m/z value?

Sometimes M²⁺ ions are formed.

Since the spectrum shows mass-to-charge ratio (m/z),

doubling the charge halves the value.

What is an atomic orbital?

A region around the nucleus that can hold up to 2 electrons with opposite spins.

How many atomic orbitals are in the s, p and d sub-shells?

Describe the shape of s and p orbitals.

1, 3 and 5

s = spherical

p = dumbbell-shaped

State the rules (3) and exceptions (2) for filling and removing electrons in sub-shells.

① Electrons fill atoms from the lowest energy level possible

② They fill empty atomic orbitals before pairing.

③ Electrons leave the highest energy level when forming ions

Exceptions: (not needed Unit 1)

① Cr and Cu have 4s¹ due to the stability of half or full d sub-shell.

② Transition metal ions lose 4s electrons before their 3d electrons.

Name and define IE1 and IE2.

First ionisation energy - the energy change when one mole of gaseous atoms forms 1 mole of gaseous 1+ ions.

Second ionisation energy - the energy change when one mole of gaseous 1+ ions form 1 mole of gaseous 2+ ions.

State and explain the 4 factors that affect ionisation energy.

Increase IE: ① increasing nuclear charge

Decrease IE: ② Increasing distance from the nucleus, ③ electron shielding and ④ electron-electron repulsion

Why is there a small drop in IE1 from p³ to p⁴ configurations?

p⁴ has two electrons in the same orbital causing a slight destabilisation due to electron-electron repulsion.

State and explain the pattern down a group for IE1.

IE decreases as the outer electron is further from the nucleus (more shells) and electron shielding is greater. Both contribute to a weaker nuclear attraction.

What does the greatest gap in a series of successive ionisation energies signify?

A change in main shell.

Eg moving from a 3s¹ configuration to a 2p⁶ configuration.

What evidence does the patterns in

(a) first ionisation energies across a period and

(b) successive ionisation energies for a given element?

a) Electron sub-shells

b) Electron shells

What is molar mass?

What is its symbol and units?

The mass of one mole of a substance.

Symbol ‘M’

Units gmol⁻¹

What is ‘amount of substance’ and what is its unit?

The number of moles

Unit, mol

State the 3 mole equations.

M=g/n

C=n/v

V=24n

where M is molar mass, g mass in grams, n number of moles, C concentration, v volume of solution in dm³ and V volume of gas in dm³.

What are ‘STP’ and ‘RTP’?

Standard temperature & pressure 0°C/100 kPa

Room temperature & pressure, usually 25°C/100 kPa

Give three equivalences to 1 dm³,

and how many dm³ in a m³?

1 dm³ = 1000 cm³ = 1L = 1000 ml

1000 dm³ = 1 m³

How many g in a kg

and how many kg in a tonne?

1000 g = 1 kg

1000 kg = 1 tonne

What is ‘water of crystallisation’ and how is it shown in a formula?

The number of water molecules in a hydrated salt.

A dot followed by a large number before H₂O

eg CuSO₄·5H₂O

The water molecules in hydrated salts can be removed when heated.

What are the new salts formed called?

Anhydrous salts

What are the 2 main steps in a water of crystallisation calculation?

① Find ‘n’ for both anhydrous salt and water.

② Find the simplest ratio by dividing through by the smallest n.

What are the 2 main steps in an empirical formula calculation?

① Find ‘n’ for all the elements.

② Find the simplest ratio by dividing through by the smallest n.

What extra information is needed to determine a molecular formula from an empirical formula, and how is it done?

Molar mass (or Mr) is needed.

M(molecular)/M(empirical) to find a multiplication factor.

What is a typical method for many mole questions involving chemical reactions?

① Find n of one substance using mole equation.

② Convert to n of another substance from balanced equation.

③ Convert n to required measurement using mole equation.

What is the ideal gas equation?

PV=nRT

P = pressure in Pa

V = volume in m³

n = number of moles

R = constant (data sheet)

T= temperature in Kelvin

What rule converts °C into K?

+273

Give 4 reasons why 100% yields are rare in chemical synthesis.

① Reactions are reversible so do not go to completion.

② Side reactions happen, making different products.

③ Making and purification steps lose product each time.

④ Impure reactants.

What is the percentage yield equation?

% yield = actual mass of product/theoretical yield x 100

Describe limiting and excess reactants

Limiting reactant gets used up and so the reaction stops.

Excess reactant is still there when the reaction has stopped.

What is atom economy?

mass of wanted product/mass of all products x 100

What is the atom economy for a reaction with one product?

100%

What are by-products?

Products from a chemical reaction that were not the desired product, also called waste products.

List factors that are desired for industrial synthesis (9!)?

Easily available resources, renewable resources,

low temperatures and pressures (so low cost/fossil fuel use/carbon emissions),

fast reactions,

high yields (minimise steps and recycle reactants),

high atom economy (to limit waste), uses for by-products,

low hazards for reactants/products, low pollution/landfill.

Compare how % yield and atom economy are related to the production process.

% yield – calculated from experimental results and affected by the production process.

Atom economy – fixed by the balanced equation and not affected by the production process.

What is an acid?

Name some common ones.

A proton donor • (Releases H⁺ ions in solution)

Strong - hydrochloric acid HCl, sulphuric acid H₂SO₄, nitric acid HNO₃.

Weak - ethanoic acid CH₃COOH (or any carboxylic acid).

What is the difference between a weak and strong acid?

A strong acid completely dissociates in water, and a weak acid partially dissociates.

What is pH?

It is a measure of H⁺ concentration.

The higher the H⁺ concentration, the lower the pH.

Y13 answer: pH = -log[H⁺]

What is a base? Give 4 examples.

A proton acceptor. • (Removes H⁺ ions from solution).

Metal oxides

Hydroxides

Carbonate

Ammonia (and amines, covered in Y13)

What is an alkali?

State the name and formula of 3 common ones.

A soluble base producing OH⁻ ions in solution.

Sodium hydroxide NaOH

Potassium hydroxide KOH

Ammonia solution NH₃

What is a covalent bond?

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

Explain the melting points/boiling points and electrical conductivity of simple covalents.

Low mps/bps because only weak intermolecular forces between molecules need to be overcome.

Insulators because there are no mobile charged particles (ie no delocalised electrons & no ions)

In ‘dot-and-cross’ diagrams, how are single, double and triple bonds denoted?

Single: one shared pair of electrons

Double: two shared pairs

Triple: three shared pairs.

What is a dative (coordinate) bond and how is it represented in displayed formulae?

One atom supplies both bonding electrons.

Once formed, it is the same as a ‘normal’ covalent bond.

Represented by an arrow from the donating atom to the accepting atom.

State the shape and bond angles for 2, 3, 4, 5 and 6 bonding pairs with no lone pairs.

2 – linear 180°

3 – trigonal planar 120°

4 – tetrahedral 109.5°

5 – trigonal bipyramidal 120°/90°/180°

6 – octahedral 90°/180°

State the shape and bond angle of molecules with

(a) 1 lone pair, 3 bonding pairs

(b) 2 lone pairs, 2 bonding pairs.

Explain the difference in bond angles.

(a) Pyramidal 107°

(b) Non-linear 104.5°

Lone pairs repel more strongly than bonding pairs, reducing the bond angle.

What is electronegativity?

What is the most electronegative element and why?

The ability of an atom to attract bonding electrons in a covalent bond.

Fluorine, as it has a small atomic radius and a high effective nuclear charge.

What is the Pauling scale and how can it be used to predict chemical bonding?

A numerical scale of electronegativity.

“Rule of thumb”

Very large differences (>1.8) - ionic.

Small differences (<0.4) - non-polar covalent.

Intermediate (≈0.4 to 1.8) - polar covalent.

What is

(a) a polar bond and

(b) a polar molecule?

(a) A bond with a permanent dipole due to a difference in electronegativity between the bonded atoms.

(b) A molecule with an overall permanent dipole due to polar bonds that do not cancel because of the molecular shape.

What is a dipole?

A separation of charge producing δ+ and δ- partial charge regions.

Why is carbon able to form so many organic compounds?

Carbon’s 4 outer electrons and a small atomic radius allow it to form stable single, double and triple bonds with itself and other elements, forming chains and rings.

Define the terms:

① hydrocarbon

② saturated

③ unsaturated

① Compound containing hydrogen and carbon only.

② All single C-C bonds.

③ At least one double or triple bond.

Define the terms:

① functional group

② homologous series

③ general formula

① The group of atoms in a molecule responsible for its characteristic chemical reactions.

② A family of compounds with the same functional group & general formula, differing by multiples of CH₂.

③ A formula involving ‘n’ representing a homologous series

What is an alkyl group?

How is it represented and name the first six.

An alkane with one H removed & formula CₙH₂ₙ₊₁.

Commonly represented by R (R′, R″ for different groups).

Methyl, ethyl, propyl, butyl, pentyl, hexyl.

Define aliphatic, alicyclic and aromatic.

Aliphatic – straight or branched chains.

Alicyclic – chains bonded in rings.

Aromatic – containing benzene rings.

Describe the difference between displayed, structural and skeletal formulae.

Displayed - all the bonds.

Structural - carbon chains with groups in brackets.

Skeletal - stick-like with Cs and Hs not shown.

Summarise the basic IUPAC naming rules (3).

① Name the longest chain with the highest-priority functional group and lowest number – this is the parent chain.

② Name and number other groups as prefixes. List them alphabetically with di-, tri-, etc. added for repeated groups.

③ Use commas between numbers, hyphens between numbers and words; no spaces.

Describe the difference between structural and stereoisomerism.

Structural – same molecular formula but different structural formulae.

Stereo – same structural formula but different arrangement of atoms in space.

What type of stereoisomerism exists in some alkenes and why does it arise?

E/Z (or cis/trans when groups are identical).

No free rotation around the double bond.

When each carbon has two different groups.

What are the priority rules for naming E/Z isomers?

Z ‘zame zide’ & E opposite

Atoms with highest atomic number take highest priority

When atoms are the same, consider the next atoms, doubling/tripling for double/triple bonds.

Why are stereoisomers difficult to separate?

They often have very similar chemical and physical properties.

Define the terms heterolytic and homolytic fission and state the species formed.

Fission is bond breaking.

Homolytic - each atom receives one electron from the bonding pair. Two radicals form.

Heterolytic - both electrons go to one atom. A negative ion and positive ion form.

Define the terms nucleophile and electrophile.

Electrophile – electron seeking and accepts an electron pair.

Nucleophile – electron rich and donates an electron pair.

What is a free radical?

Describe its reactivity and how it is represented?

An atom or group of atoms with an unpaired electron.

Highly reactive due to the unpaired electron.

A dot shows the unpaired electron – eg Cl·

Define addition, substitution, elimination and polymerisaiton reactions.

Addition: atom(s) are added to a molecule.

Substitution: atom(s) replace others.

Elimination: atom(s) are removed from a molecule.

Polymerisation: many small molecules join to form a large macromolecular polymer chain.

What does a curly arrow represent and where should it start?

The movement of a pair of electrons.

From the centre of a bond or from a lone pair of electrons.

Explain the use of [O] and [H] are in organic equations.

[O] represents oxygen supplied by an oxidising agent.

[H] represents hydrogen supplied by a reducing agent.

A shorthand used to simplify balanced equations.

Define the term ‘reagent’.

A substance used in a chemical reaction.

It refers not only to the reactants, but also catalysts, indicators, buffers, or drying agents etc.

What is the difference between a hazard and a risk, and how can risks be reduced?

Hazard = potential to cause harm

Risk = likelihood that harm will occur

Work on a smaller scale, take precautions specific to the hazard, and use alternatives if possible

What are the two main reactions for alkanes and what are they mainly used for?

Combustion and photochemical substitution.

Main use – fuels.

Why are alkanes unreactive? (2)

High bond enthalpies in both C─C and C─H.

Non-polar.

Explain the bonding, general formulae, molecular shape and bond angles in alkanes.

All single bonds so saturated.

CₙH₂ₙ₊₂ (straight/branched) CₙH₂ₙ (cyclic)

Tetrahedral backbone with 109.5° bond angles.

Describe and explain the effect of

(a) chain length and

(b) branching on the boiling points of alkanes.

The longer the chain the higher the boiling point because London forces are stronger.

The straighter the chain the higher the boiling point because molecules can get closer together and so London forces are stronger.

The stronger the forces, the more energy is needed to separate them.

Crude oil is described as a finite resource.

What does this mean?

It is non-renewable and if we continue to use it, it will eventually run out.

(Use is faster than formation)

Describe industrial fractional distillation of crude oil.

Separates large crude oil mixture into smaller mixtures called fractions.

① Oil heated to vaporise.

② Vapour moves up column which cools with height.

③ Molecules condense when temperature reaches bp.

④ Small molecular fractions near top, large near bottom.

Name and describe two small molecule fractions from crude oil.

LPG (liquid petroleum gas) C₁ to C₄.

Petrol C₅ to C₁₀.

What is cracking and why is it useful?

Long chained alkanes are broken down into smaller alkane and alkenes by breaking a C-C bond.

Smaller molecules are in great demand (ie petrol), larger ones are in excess.

Describe the conditions needed for catalytic cracking.

Aluminium oxide catalyst and high temperature

Describe reforming and why it is necessary?

Straight chain-alkanes turned into branched or cyclic alkanes, by heating them with a platinum catalyst.

It makes them burn as fuels more efficiently.

What are the products of complete and incomplete combustion of hydrocarbons, and what problems do they cause?

Complete (CO₂ & H₂O) Incomplete (C or CO & H₂O)

CO₂ – greenhouse gas – global warming.

CO (carbon monoxide) – toxic gas.

C (soot) blocks machines/asthma.

Summarise the 6 combustion pollutants, the problems and how they are reduced .

CO₂ – global warming – alternative energies, CC

CO – toxic, colourless & odourless – CC, good O₂ supply

C – soot, asthma – good O₂ supply

NOₓ – from high T/P in engine – asthma, acid rain – CC

Unburnt hydrocarbons – from engines – asthma – CC

SO₂ – from power stations, acid rain – react with CaO

What is carbon neutral?

A process that releases the same amount of carbon dioxide (usually by burning) as was absorbed from the air by photosynthesis.

What is bioethanol and is it carbon neutral?

A renewable fuel made by fermenting plant sugars.

No, but better than fossil fuels

CO₂ from burning = CO₂ absorbed when growing,

but farming, distillation and transport produce emissions.

Under what conditions could H₂ fuel be considered carbon neutral?

When the electricity needed to make H₂ comes from a renewable source (eg solar).

Name the type of reaction that changes alkanes into halogenoalkanes.

(Photochemical) free radical substitution.

State and describe the three stages in a free radical substitution reaction.

Initiation - a molecule breaks into 2 radicals.

Propagation - a radical and a molecule react to form a different radical and molecule.

Termination - 2 radicals join to form a molecule.

What are alkenes?

State functional group, general formula, molecular shape and bond angles.

Hydrocarbons with at least one double bond.

CₙH₂ₙ

Trigonal planar around the double bond.

≈120° bond angles.

Why are alkenes more reactive than alkanes, and what type of reactions do they undergo?

Double bond made of σ- and π-bond.

Electrophiles attracted to high electron density on π-bond.

Addition because π-bond is weaker and so more easily broken than σ.

So electrophilic addition.