Edexcel IAL Chemistry U1/U2 高频定义与解释

The solution turns orange/brown because chlorine oxidises bromide ions to bromine; chlorine is a stronger oxidising agent than bromine.

1. chlorine displaces bromine
2. Br⁻ is oxidised to Br₂
3. orange/brown bromine forms
4. chlorine is more oxidising

A species that donates a pair of electrons to form a covalent bond.

1. electron-pair donor
2. forms a covalent bond
3. often has a lone pair or negative charge

Particles have higher kinetic energy, so they collide more frequently and a greater proportion of particles have energy equal to or greater than Ea; therefore there are more successful collisions per unit time.

1. higher kinetic energy
2. more frequent collisions
3. greater proportion with E ≥ Ea
4. more successful/effective collisions per unit time

Lone pairs repel bonding pairs more strongly than bonding pairs repel each other, so the bonding pairs are pushed closer together and the bond angle decreases.

1. state number of bonding/lone pairs when relevant
2. lone pair-bond pair repulsion is stronger
3. bonding pairs move closer
4. bond angle decreases

The minimum energy that particles must have for a reaction to occur when they collide.

1. minimum energy
2. particles/collisions
3. reaction occurs

Curly arrow from the C=C π bond to the electrophile, bond-breaking arrow in the reagent, formation of a carbocation/intermediate, then attack by a nucleophile.

1. arrow starts from C=C π bond
2. show induced dipole / bond-breaking arrow
3. show carbocation or suitable intermediate
4. nucleophile arrow starts from lone pair/negative charge

Add dilute nitric acid then silver nitrate. Cl⁻ gives white AgCl soluble in dilute NH₃; Br⁻ gives cream AgBr soluble in concentrated NH₃; I⁻ gives yellow AgI insoluble in NH₃.

1. acidify with nitric acid
2. AgNO₃ produces silver halide precipitate
3. Cl⁻ white soluble in dilute ammonia
4. Br⁻ cream soluble in concentrated ammonia
5. I⁻ yellow insoluble in ammonia

The equilibrium shifts to the side with fewer moles of gas, reducing the pressure.

1. compare moles of gas on each side
2. shifts to fewer gaseous molecules
3. opposes the pressure increase

Down the group, atoms are larger and outer electrons are more shielded, so the nucleus attracts an incoming electron less strongly.

1. atomic radius increases
2. shielding increases
3. attraction for incoming electron decreases
4. oxidising power decreases

Initiation: Cl₂ → 2Cl• under UV. Propagation: Cl• + CH₄ → HCl + CH₃•; CH₃• + Cl₂ → CH₃Cl + Cl•. Termination: two radicals combine.

1. initiation is homolytic fission under UV
2. propagation forms alkyl radical
3. propagation regenerates halogen radical
4. termination combines radicals

A catalyst provides an alternative reaction pathway with a lower activation energy, so a greater proportion of particles have E ≥ Ea.

1. alternative pathway
2. lower activation energy
3. greater proportion of particles exceed Ea
4. catalyst is not used up

The simplest whole-number ratio of atoms of each element in a compound.

1. simplest whole-number ratio
2. atoms/elements in a compound

Larger Group 2 cations have lower charge density and polarise the carbonate ion less, so the carbonate ion is less distorted and decomposes less readily.

1. cation radius increases
2. charge density decreases
3. less polarisation of CO₃²⁻
4. carbonate is more stable

A species with an unpaired electron.

1. species / atom / group
2. has an unpaired electron
3. usually shown with a dot

A large jump shows the next electron is removed from an inner shell closer to the nucleus; the number of electrons removed before the jump equals the number of outer-shell electrons.

1. identify the large jump
2. next electron is in an inner shell
3. inner electron is closer to nucleus / less shielded
4. electrons before the jump = outer-shell electrons

Gentle oxidation and distillation gives an aldehyde; heating under reflux with excess acidified potassium dichromate(VI) gives a carboxylic acid.

1. acidified potassium dichromate(VI)
2. distillation removes aldehyde
3. reflux/excess oxidant forms carboxylic acid
4. orange to green colour change

Shake with bromine water; orange/brown bromine water is decolourised.

1. use bromine water
2. orange/brown to colourless
3. alkanes do not decolourise it without UV

The enthalpy change required to break one mole of a specified covalent bond in gaseous molecules, averaged over a range of compounds.

1. break one mole of specified covalent bonds
2. in gaseous molecules
3. mean value over different compounds

Warm/reflux with aqueous potassium hydroxide or aqueous sodium hydroxide; the reaction is nucleophilic substitution by OH⁻.

1. aqueous KOH/NaOH
2. warm or reflux
3. nucleophilic substitution
4. OH⁻ replaces halide

Breaking a covalent bond so that each bonded atom receives one electron from the bond, forming radicals.

1. covalent bond breaks
2. one electron goes to each atom
3. free radicals form

A σ bond is formed by direct/head-on overlap of orbitals along the internuclear axis; a π bond is formed by sideways overlap of adjacent p orbitals above and below the σ bond.

1. σ: direct / head-on overlap
2. σ overlap is along the internuclear axis
3. π: sideways overlap of p orbitals
4. π electron density lies above and below the bond axis

Heat/reflux with ethanolic potassium hydroxide; H and X are eliminated to form an alkene.

1. ethanolic KOH
2. heat/reflux
3. forms alkene
4. elimination of HX

Open the C=C double bond to a C-C single bond, keep the substituents on the same carbons, put brackets around the repeating unit and place n outside.

1. C=C becomes C-C
2. substituents retained
3. continuation bonds go through brackets
4. n outside brackets

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

1. same element
2. same proton number
3. different neutron number

The electrostatic attraction between oppositely charged ions.

1. electrostatic attraction
2. oppositely charged ions

The electrostatic attraction between positive metal ions and delocalised electrons.

1. positive metal ions
2. delocalised electrons
3. electrostatic attraction

Group 2 sulfates become less soluble down the group; BaSO₄ is very insoluble and forms a white precipitate.

1. sulfate solubility decreases down Group 2
2. barium sulfate is insoluble
3. white precipitate

An O-H stretch in alcohols is broad around 3200-3600 cm⁻¹; a C=O absorption is strong around 1700 cm⁻¹.

1. broad O-H around 3200-3600 cm⁻¹
2. strong C=O around 1700 cm⁻¹
3. use fingerprint region to compare with database when needed

The measured temperature change is smaller than the true value, so the calculated energy change is too small in magnitude.

1. temperature change is lower
2. energy calculated is lower
3. enthalpy magnitude is underestimated

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

1. electrostatic attraction
2. between nuclei and shared pair
3. shared pair of electrons

A covalent bond in which both electrons in the shared pair are donated by the same atom.

1. it is a covalent bond
2. both electrons come from one atom
3. the other species accepts the lone pair

The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12.

1. weighted mean mass of an atom of the element
2. compared with 1/12 of the mass of one atom of carbon-12
3. use isotopic abundance when calculating it

A redox reaction in which the same element is both oxidised and reduced.

1. same element/species
2. is oxidised
3. is reduced

Steam with a phosphoric acid catalyst at high temperature and pressure.

1. steam
2. phosphoric acid catalyst
3. high temperature/pressure

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

1. ability/power of an atom
2. attracts bonding pair of electrons
3. in a covalent bond

Group 2 hydroxides become more soluble down the group; barium hydroxide solution can be used to test for sulfate ions, giving white BaSO₄.

1. solubility increases down the group
2. Ba²⁺ + SO₄²⁻ gives white precipitate
3. BaSO₄ is insoluble

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

1. one mole of gaseous atoms
2. remove one electron from each atom
3. forms one mole of gaseous 1+ ions

A secondary alcohol is oxidised to a ketone; a tertiary alcohol is not oxidised under these conditions.

1. secondary alcohol forms ketone
2. tertiary alcohol has no reaction/no oxidation
3. dichromate changes orange to green only if oxidation occurs

The C-I bond has a lower bond enthalpy than C-Br and C-Cl, so it is weaker and breaks more easily.

1. C-I bond is weakest
2. lower bond enthalpy
3. bond breaks more easily
4. faster hydrolysis

A larger molecule has more electrons and a larger surface area, so stronger London forces act between molecules; more energy is needed to overcome these intermolecular forces.

1. more electrons / larger electron cloud
2. larger surface contact
3. stronger London forces
4. more energy needed to overcome intermolecular forces

There must be restricted rotation about the C=C double bond and each carbon of the C=C must have two different groups attached.

1. restricted rotation around C=C
2. each C has two different groups
3. assign priority using atomic number when needed

When a system at equilibrium is disturbed, the equilibrium shifts to oppose the change.

1. system at equilibrium
2. a condition is changed
3. equilibrium shifts to oppose the change

Compounds with the same molecular formula but different structural formulae / different arrangement of atoms.

1. same molecular formula
2. different structural formulae
3. different arrangement/connectivity

Heat with concentrated sulfuric acid or pass vapour over hot aluminium oxide; water is eliminated to form an alkene.

1. concentrated H₂SO₄ or hot Al₂O₃
2. elimination/dehydration
3. alkene product
4. water eliminated

The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions, with all substances in their standard states.

1. one mole of substance
2. complete combustion
3. in oxygen
4. standard conditions/states

The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.

1. one mole of compound
2. formed from elements
3. elements in standard states
4. standard conditions

C-C and C-H bonds are strong / have high bond enthalpies, and the molecules are non-polar, so they are not readily attacked by electrophiles or nucleophiles.

1. C-C/C-H bonds have high bond enthalpies
2. alkanes are non-polar
3. no region of high electron density / no polar bond for attack

The atom or group of atoms responsible for the characteristic chemical reactions of an organic compound.

1. atom or group of atoms
2. responsible for characteristic chemical reactions

A species that accepts a pair of electrons to form a covalent bond.

1. electron-pair acceptor
2. forms a covalent bond
3. is attracted to an electron-rich region

A series of organic compounds with the same functional group, similar chemical properties and successive members differing by CH₂.

1. same functional group
2. similar chemical properties
3. successive members differ by CH₂
4. same general formula if relevant

Breaking a covalent bond so that both electrons from the bond go to one of the bonded atoms, forming ions.

1. covalent bond breaks
2. both bonding electrons go to one atom
3. ions form

In a closed system, the forward and reverse reactions occur at the same rate, so the concentrations of reactants and products remain constant.

1. closed system
2. forward and reverse reactions
3. same rate
4. constant concentrations