AQA Chemistry Year 1 – Inorganic & Organic Chemistry 1

Key vocabulary terms and their definitions covering Periodicity, Group 2 & Group 7 chemistry, organic mechanisms, analytical techniques and environmental aspects from the AQA AS/A-level Year 1 Chemistry guide.

Periodicity

The repeating pattern of physical and chemical properties of the elements across different periods of the Periodic Table.

Atomic-radius trend across Period 3

Decreases from Na to Ar because nuclear charge increases while shielding remains similar, pulling outer electrons closer.

First-ionisation-energy trend across a period

Generally increases from left to right due to greater nuclear charge and smaller atomic radius.

Melting-point trend across Period 3

Rises to silicon (giant covalent), then falls sharply for molecular elements P, S, Cl and to very low for Ar.

s-Block element

An element whose outermost electron(s) occupy an s-sub-shell (e.g. Na, Mg).

p-Block element

An element whose outermost electron(s) occupy a p-sub-shell (e.g. Cl, Si).

d-Block element

An element whose last added electrons occupy a d-sub-shell; includes the transition metals.

Group 2 (alkaline-earth) metals

Elements with outer configuration ns²; show increasing reactivity and decreasing first ionisation energy down the group.

Group 2 atomic-radius trend

Increases down the group because extra shells outweigh increased nuclear charge.

Group 2 first-ionisation-energy trend

Decreases down the group due to greater distance and shielding of outer electrons.

Group 2 melting-point trend

Generally falls from Mg to Ba as metallic bonds weaken; Mg is anomalously low.

Solubility trend of Group 2 hydroxides

Increases from Mg(OH)₂ (almost insoluble) to Ba(OH)₂ (quite soluble).

Solubility trend of Group 2 sulfates

Decreases down the group; BaSO₄ is virtually insoluble.

Barium meal

Suspension of insoluble BaSO₄ taken by patients so soft tissues show up during X-rays.

Magnesium hydroxide use

Active ingredient in indigestion tablets; neutralises excess stomach acid.

Calcium hydroxide use

‘Slaked lime’ spread on fields to neutralise acidic soils.

Flue-gas desulfurisation

SO₂ from power-station gases is removed by reacting with CaO or CaCO₃ to form solid CaSO₃.

Magnesium in titanium extraction

Reduces TiCl₄ at ≈ 700 °C in an Ar atmosphere: TiCl₄ + 2 Mg → Ti + 2 MgCl₂.

Test for sulfate ion

Add acidified BaCl₂; a white precipitate of BaSO₄ confirms SO₄²⁻.

Halogen boiling-point trend

Increases F₂ → I₂ due to stronger van der Waals forces as Mr rises.

Halogen electronegativity trend

Decreases down the group as atomic radius and shielding increase.

Oxidising power of halogens

Cl₂ > Br₂ > I₂; shown by displacement reactions of halide ions.

Reducing power of halide ions

I⁻ > Br⁻ > Cl⁻; iodide reduces H₂SO₄ to H₂S, bromide only to SO₂, chloride not at all.

Silver-nitrate test for halides

Ag⁺ + X⁻ → AgX: white AgCl dissolves in dilute NH₃; cream AgBr dissolves in conc. NH₃; yellow AgI is insoluble.

Chlorine + cold dilute NaOH

Produces NaCl, H₂O and bleach NaOCl (chlorate(I) ions).

Chlorine + water

Cl₂ + H₂O ⇌ HCl + HOCl; HOCl kills bacteria in drinking water/swimming pools.

Fractional distillation of crude oil

Separates hydrocarbons by boiling range using a column with temperature gradient.

Cracking

Thermal or catalytic breakdown of long-chain alkanes into shorter alkanes and alkenes.

Free-radical substitution

The UV-initiated halogenation of alkanes via radical chain mechanism (initiation, propagation, termination).

Nucleophile

Electron-pair donor attracted to electron-deficient centres (e.g. OH⁻, CN⁻, NH₃).

Nucleophilic substitution

Mechanism in which a nucleophile replaces a halogen in a haloalkane, forming alcohols, nitriles or amines.

Elimination reaction of haloalkanes

Hot ethanolic OH⁻ removes H and X to give an alkene and water (and KX).

Electrophile

Electron-pair acceptor that attacks regions of high electron density, e.g. H⁺, Br₂.

Electrophilic addition

Typical reaction of alkenes where electrophile adds across C=C forming saturated product.

Markovnikov’s rule (major product)

In HX addition to unsymmetrical alkenes, H bonds to the C with more H atoms because it forms the more stable carbocation.

E–Z isomerism

Stereoisomerism arising from restricted rotation about C=C; E = highest-priority groups opposite, Z = together.

Addition polymerisation

Many alkene monomers add to form a long saturated chain with no small molecule by-product.

Poly(chloroethene) (PVC)

Polymer of CH₂=CHCl; unplasticised PVC is rigid (window frames), plasticised PVC is flexible (cables, boots).

Alcohol dehydration

Concentrated H₂SO₄ or H₃PO₄ at 170 °C eliminates water from an alcohol to form an alkene.

Fermentation of glucose

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂ at 35 °C, anaerobic, using yeast enzymes; produces bioethanol.

Hydration of ethene

Ethene + steam at 300 °C, 60 atm, H₃PO₄ catalyst → ethanol (electrophilic addition).

Primary alcohol oxidation products

Gives aldehyde (distillation) then carboxylic acid (reflux) with acidified K₂Cr₂O₇.

Secondary alcohol oxidation

Produces a ketone when refluxed with acidified dichromate; tertiary alcohols resist oxidation.

Tollens’ reagent test

Colourless [Ag(NH₃)₂]⁺; aldehydes reduce it to silver mirror, ketones give no change.

Fehling’s solution test

Blue Cu²⁺ complex; aldehydes give red Cu₂O precipitate on warming, ketones do not.

IR absorption of O–H (acid)

Very broad peak 2500–3000 cm⁻¹ in infrared spectrum.

IR absorption of C=O

Sharp strong peak 1680–1750 cm⁻¹ characteristic of carbonyl groups (aldehydes, ketones, acids, esters).

Fingerprint region

Complex IR region < 1500 cm⁻¹ unique to each molecule; used to match unknowns with spectra databases.

Molecular-ion peak (mass spect.)

Peak with highest m/z; corresponds to relative molecular mass (M⁺•) of the molecule.

Greenhouse gas absorption

CO₂, CH₄ and H₂O absorb IR radiation via bond vibrations, contributing to the greenhouse effect.

Ozone depletion mechanism

CFCl₃ → CFCl₂• + Cl•; Cl• + O₃ → ClO• + O₂; ClO• + O₃ → Cl• + 2 O₂ — radicals catalyse breakdown of ozone.